@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99323, title ="Grand Canyon provenance for orthoquartzite clasts in the lower Miocene of coastal southern California", author = "Sabbeth, Leah and Wernicke, Brian P.", journal = "Geosphere", volume = "15", number = "6", pages = "1973-1998", month = "December", year = "2019", doi = "10.1130/ges02111.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191017-091038239", note = "© 2019 The Authors. This paper is published under the terms of the CC‑BY-NC license. \n\nReceived 12 December 2018; Revision received 15 May 2019; Accepted 30 July 2019. \n\nThis research was supported by National Science Foundation (NSF) grants EAR 10-19896 and EAR 14-51055 awarded to B. Wernicke, EAR 17-28690 awarded to J. Stock, and OPP 13-41729 awarded to J. Kirschvink. We also acknowledge NSF grant EAR 16-49254 awarded to G. Gehrels at the University of Arizona for support of the Arizona LaserChron Center. We thank Jonathan Hagstrum of the U.S. Geological Survey for providing a copy of the manuscript containing paleomagnetic data of D. Elston and S. Grommé (1994) from the Shinumo Formation. Guidance from the associate editor and reviewers R. Molina-Garza and R. V. Ingersoll substantially improved the manuscript.", revision_no = "21", abstract = "Orthoquartzite detrital source regions in the Cordilleran interior yield clast populations with distinct spectra of paleomagnetic inclinations and detrital zircon ages that can be used to trace the provenance of gravels deposited along the western margin of the Cordilleran orogen. An inventory of characteristic remnant magnetizations (CRMs) from >700 sample cores from orthoquartzite source regions defines a low-inclination population of Neoproterozoic–Paleozoic age in the Mojave Desert–Death Valley region (and in correlative strata in Sonora, Mexico) and a moderate- to high-inclination population in the 1.1 Ga Shinumo Formation in eastern Grand Canyon. Detrital zircon ages can be used to distinguish Paleoproterozoic to mid-Mesoproterozoic (1.84–1.20 Ga) clasts derived from the central Arizona highlands region from clasts derived from younger sources that contain late Mesoproterozoic zircons (1.20–1.00 Ga). Characteristic paleomagnetic magnetizations were measured in 44 densely cemented orthoquartzite clasts, sampled from lower Miocene portions of the Sespe Formation in the Santa Monica and Santa Ana mountains and from a middle Eocene section in Simi Valley. Miocene Sespe clast inclinations define a bimodal population with modes near 15° and 45°. Eight samples from the steeper Miocene mode for which detrital zircon spectra were obtained all have spectra with peaks at 1.2, 1.4, and 1.7 Ga. One contains Paleozoic and Mesozoic peaks and is probably Jurassic. The remaining seven define a population of clasts with the distinctive combination of moderate to high inclination and a cosmopolitan age spectrum with abundant grains younger than 1.2 Ga. The moderate to high inclinations rule out a Mojave Desert–Death Valley or Sonoran region source population, and the cosmopolitan detrital zircon spectra rule out a central Arizona highlands source population. The Shinumo Formation, presently exposed only within a few hundred meters elevation of the bottom of eastern Grand Canyon, thus remains the only plausible, known source for the moderate- to high-inclination clast population. If so, then the Upper Granite Gorge of the eastern Grand Canyon had been eroded to within a few hundred meters of its current depth by early Miocene time (ca. 20 Ma). Such an unroofing event in the eastern Grand Canyon region is independently confirmed by (U-Th)/He thermochronology. Inclusion of the eastern Grand Canyon region in the Sespe drainage system is also independently supported by detrital zircon age spectra of Sespe sandstones. Collectively, these data define a mid-Tertiary, SW-flowing “Arizona River” drainage system between the rapidly eroding eastern Grand Canyon region and coastal California.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88809, title ="Subsidence history of the Ediacaran Johnnie Formation and related strata of southwest Laurentia: Implications for the age and duration of the Shuram isotopic excursion and animal evolution", author = "Witkosky, Rebecca and Wernicke, Brian P.", journal = "Geosphere", volume = "14", number = "5", pages = "2245-2276", month = "October", year = "2018", doi = "10.1130/GES01678.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180815-081811088", note = "© 2018 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY-NC license. \n\nReceived Feb 10, 2018; Revised Apr30, 2018; Accepted Jul 19, 2018. \n\nWe are grateful to Gillian Anderson, Leah Sabbeth, Fenfang Wu, and the late Lindsey Hedges for assistance in the field and laboratory, and to Associate Editor Christopher J. Spencer and reviewer Tony Prave for insightful and constructive reviews. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant 1144469 awarded to R. Witkosky, and grant EAR 14-51055 awarded to B. Wernicke.", revision_no = "18", abstract = "The Johnnie Formation and associated Ediacaran strata in southwest Laurentia are ~3000 m thick, with a Marinoan cap carbonate sequence at the bottom, and a transition from Ediacaran to Cambrian fauna at the top. About halfway through the sequence, the Shuram negative carbon isotopic excursion occurs within the Rainstorm Member near the top of the Johnnie Formation, followed by a remarkable valley incision event. At its type locality in the northwest Spring Mountains, Nevada, the Johnnie lithostratigraphy consists of three distinctive sand-rich intervals alternating with four siltstone/carbonate-rich intervals, which appear correlative with other regional \u00adJohnnie Formation outcrops. Carbon isotope ratios in the sub–Rainstorm Member part of the Johnnie Formation are uniformly positive for at least 400 m below the Shuram excursion and compare well with sub–Shuram excursion profiles from the \u00adKhufai Formation in Oman. There is historical consensus that the Johnnie and overlying formations were deposited on a thermally subsiding passive margin. Following previous authors, we used Paleozoic horizons of known biostratigraphic age to define a time-dependent exponential sub\u00adsidence model, and extrapolated the model back in time to estimate the ages of the Shuram excursion and other prominent Ediacaran horizons. The model suggests that the Shuram excursion occurred from 585 to 579 Ma, and that incision of the Rainstorm Member shelf occurred during the 579 Ma Gaskiers glaciation. It further suggests that the base of the Johnnie Formation is ca. 630 Ma, consistent with the underlying Noonday Formation representing a Marinoan cap carbonate sequence. Our results contrast with suggestions by previous workers that the Shuram excursion followed the Gaskiers event by some 20–30 m.y. We suggest instead that the Shuram and Gaskiers events were contemporaneous with the biostratigraphic transition from acantho\u00admorphic to leiospherid acritarchs, and with the first appearance of widespread macroscopic animal life, 38 m.y. prior to the Ediacaran-Cambrian boundary.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/88945, title ="Fluid Flow, Brecciation, and Shear Heating on Faults: Insights from Carbonate Clumped-Isotope Thermometry", author = "Swanson, E. M. and Wernicke, B. P.", journal = "Tectonics", volume = "37", number = "9", pages = "2938-2960", month = "September", year = "2018", doi = "10.1029/2018TC004984", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180820-083434380", note = "© 2018 American Geophysical Union. \n\nReceived 7 FEB 2018; Accepted 4 AUG 2018; Accepted article online 17 AUG 2018; Published online 8 SEP 2018. \n\nWe are indebted to two anonymous reviewers for comments that contributed substantially to the clarity of presentation. This research was supported by National Science Foundation grant EAR 12-50565 awarded to B. P. Wernicke and J. Eiler and by the Caltech Tectonics Observatory of the Gordon and Betty Moore Foundation. Data presented and discussed here are all in the tables and supplementary information presented in this manuscript.", revision_no = "23", abstract = "Slip on gently dipping detachments in the brittle crust has been enigmatic for decades, because fracture mechanics laws predict frictional resistance is too great for sliding to occur, except under rather unusual circumstances. The Miocene Mormon Peak detachment in Nevada and the Eocene Heart Mountain detachment in Wyoming are two well‐studied examples of upper crustal, carbonate‐hosted low‐angle detachments, with highly debated slip processes. Both low‐angle faults were active during regional magmatism, and a number of proposed slip mechanisms involve magmatic fluids, frictional heating, or both. To address the role that magmatic fluids and frictional heating may have played in reducing friction, we measured clumped‐isotope ratios on 137 carbonate samples from these faults. The majority of fault breccias and gouges on the detachment slip surface record temperatures that are colder than the host rock. Surprisingly, samples from within 5 m of the Heart Mountain detachment average just 65 °C, and not a single sample (out of 37 measurements, excluding metamorphosed host rock at White Mountain) records a temperature greater than 90 °C. Along both faults, most samples are depleted in δ^(18)O relative to the host rock, indicating that meteoric, not magmatic, fluids were present and interacting with the fault rock. However, a few samples preserve temperatures of over 160 °C, which, based on textural and geochemical criteria, are difficult to explain other than by frictional heating during slip. These temperatures are recorded in one sample directly on the Mormon Peak detachment slip surface and in two hanging wall localities above the Heart Mountain detachment.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/84111, title ="Late Neogene−Quaternary tephrochronology, stratigraphy, and paleoclimate of Death Valley, California, USA", author = "Knott, Jeffrey R. and Machette, Michael N.", journal = "Geological Society of America Bulletin", volume = "130", number = "7-8", pages = "1231-1255", month = "July", year = "2018", doi = "10.1130/B31690.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180104-161037276", note = "© 2018 Geological Society of America. \n\nManuscript Received 27 October 2016; Revised Manuscript Received 2 October 2017; Manuscript Accepted 16 November 2017. \n\nThis project represents an assimilation of several different projects independently completed by the authors over a span of nearly two decades. Support for these projects was from the National Science Foundation (EAR-94-06029 to Wells); California State University–Fullerton Undergraduate Research and Creativity Awards (to Knott); American Chemical Society Petroleum Research Fund (43505-B8 and 46581-UFS to Knott); and the U.S. Geological Survey. \n\nThe list of people who provided stimulating discussion and criticisms over the years is too long to list, but we thank them all. We’d like to especially thank the late Bennie Troxel and the late Lauren Wright for\nthe inspiration and friendship they generously provided as they shared their geologic knowledge of the area with those of us who knew them. Steve Okubo assisted with the geologic mapping in the Kit Fox Hills. This study was completed under permits granted by the U.S. Department of the Interior National Park Service. We thank Darrel Cowan, Leah Morgan, David Miller, associate editor Michael Elliot Smith and editor Bradley S. Singer for their insightful reviews. Any use of trade, firm or product name is for descriptive purposes only and does not imply endorsement by the U.S. government.", revision_no = "19", abstract = "Sedimentary deposits in midlatitude continental basins often preserve a paleoclimate record complementary to marine-based records. However, deriving that paleoclimate record depends on having well-exposed deposits and establishing a sufficiently robust geochronology. After decades of research, we have been able to correlate 77 tephra beds exposed in multiple stratigraphic sections in the Death Valley area, California, United States. These correlations identify 25 different tephra beds that erupted from at least five different volcanic centers from older than 3.58 Ma to ca. 32 ka. We have informally named and determined the ages for seven previously unrecognized beds: ca. 3.54 Ma tuff of Curry canyon, ca. 3.45 Ma tuff of Furnace Creek, ca. 3.1 Ma tuff of Kit Fox Hills, ca. 3.1 Ma tuff of Mesquite Flat, ca. 3.15 Ma tuff of Texas Spring, 3.117 ± 0.011 Ma tuff of Echo Canyon, and the ca. 1.3 Ma Amargosa ash bed. Several of these tephra beds are found as far northeast as central Utah and could be important marker beds in western North America.\nOur tephrochronologic data, combined with magnetic polarity data and ^(40)Ar/^(39)Ar age determinations, redefine Neogene sedimentary deposits exposed across 175 km^2 of the Death Valley area. The alluvial/lacustrine Furnace Creek Formation is a time-transgressive sedimentary sequence ranging from ca. 6.0 to 2.5 Ma in age. The ca. 2.5−1.7 Ma Funeral Formation is typically exposed as a proximal alluvial-fan facies overlying the Furnace Creek Formation. We have correlated deposits in the Kit Fox Hills, Salt Creek, Nova Basin, and southern Death Valley with the informally named ca. 1.3−0.5 Ma Mormon Point formation. In addition, our correlation of the late Pleistocene Wilson Creek ash bed 15 in the Lake Rogers deposits represents the first unambiguous sequences deposited during the Last Glacial Maximum (marine isotope stage [MIS] 2) in Death Valley.\nBased on this new stratigraphic framework, we show that the Pliocene and Pleistocene climate in Death Valley is consistent with the well-established marine tropical/subtropical record. Pluvial lakes in Death Valley and Searles Valley began to form ca. 3.5−3.4 Ma in the late Pliocene during MIS MG5. Initiation of lakes in these two hydrologically separated valleys at the same time at the beginning of a cooling trend in the marine climate record suggests a link to a cooler, wetter (glacial) regional climate in North America. The Death Valley lake persisted until ca. 3.30 Ma, at the peak of the M2 glaciation, after which there is no evidence of Pliocene lacustrine deposition, even at the peak of the Northern Hemisphere Glaciation (ca. 2.75 Ma). If pluvial lakes in the Pliocene are an indirect record of glacial climate conditions, as they are for the Pleistocene, then a glacial climate was present in western North America for ∼200,000 yr during the Pliocene, encompassing MIS MG5−M2.\nPleistocene pluvial lakes in Death Valley that formed ca. 1.98−1.78 Ma, 1.3−1.0 Ma, and ca. 0.6 Ma (MIS 16) are consistent with other regional climate records that indicate a regional glacial climate; however, Death Valley was relatively dry at ca. 0.77 Ma (MIS 19), when large lakes existed in other basins. The limited extent of the MIS 2 marsh/shallow lake in the Lake Rogers basin of northern Death Valley reflects the well-known regional glacial climate at that time; however, Death Valley received relatively lower inflow and rainfall in comparison.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/82830, title ="Timing of exhumation, Wheeler Pass thrust sheet, southern Nevada and California: Late Jurassic to middle Cretaceous evolution of the southern Sevier fold-and-thrust belt", author = "Giallorenzo, M. A. and Wells, M. L.", journal = "Geological Society of America Bulletin", volume = "130", number = "3-4", pages = "558-579", month = "March", year = "2018", doi = "10.1130/B31777.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171101-112601399", note = "© 2017 Geological Society of America. \n\nManuscript Received 21 February 2017; Revised Manuscript Received 14 July 2017; Manuscript Accepted 3 August 2017. \n\nThis research was funded by National Science Foundation grants EAR-1050073 to Wells and EAR-1050069 to Yonkee, Geological Society of America grants to Giallorenzo, and the Nevada Petroleum Society and ExxonMobil. We thank Roman Kislitsyn, who greatly assisted in zircon helium analyses at both the University of Kansas and the University of Texas at Austin. We appreciate the helpful comments provided by Associate Editor B. Carrapa, reviewer G. Axen, and an anonymous reviewer, which improved this manuscript.", revision_no = "21", abstract = "Zircon (U-Th)/He (ZHe) thermochronologic data for 46 samples from the Wheeler Pass thrust sheet, which carries thick passive-margin strata and is discontinuously exposed across the southern part of the Sevier fold-and-thrust belt, record Late Jurassic cooling related to exhumation during early thrust slip, and local middle Cretaceous cooling related to footwall basement imbrication. Within the frontal part of the Wheeler Pass sheet exposed in the northwest Spring Mountains, ZHe ages decrease from ca. 160 to 140 Ma over a paleodepth interval of ∼6 to 9 km in Devonian to Lower Cambrian strata, interpreted to record exhumation and enhanced cooling above a frontal ramp, followed by slow cooling. A similar pattern of ZHe ages occurs over a more limited paleodepth range exposed within the Resting Spring Range. To the south in the Nopah Range, ZHe ages of ca. 140 Ma in Lower Cambrian strata record early cooling, followed by slow cooling until ca. 100 Ma. ZHe ages in underlying Paleoproterozoic basement rocks decrease from ca. 100 to 85 Ma over a paleodepth interval of ∼9 to 12 km, interpreted to record uplift, exhumation, and cooling during footwall basement imbrication as slip was transferred eastward onto the Keystone thrust system. Late Jurassic slip on the Wheeler Pass thrust overlapped with deformation along the NW-trending East Sierran thrust system, early hinterland crustal thickening, and growth of the Sierra magmatic arc, and may have been correlative with early deformation in the Central Nevada thrust belt. Slip on the Wheeler Pass thrust preceded major slip on other thrust sheets that carried thick passive-margin strata in more northern parts of the Sevier belt, probably reflecting the influence of different initial widths and tapers of the passive-margin sedimentary wedge.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83921, title ="Thermochronometry across the Austroalpine-Pennine boundary, Central Alps, Switzerland: Orogen-perpendicular normal fault slip on a major ‘overthrust’ and its implications for orogenesis", author = "Price, Jason B. and Wernicke, Brian P.", journal = "Tectonics", volume = "37", number = "3", pages = "724-757", month = "March", year = "2018", doi = "10.1002/2017TC004619", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171214-105427229", revision_no = "35", abstract = "Fifty-one new and 309 published thermochronometric ages (nine systems with closure temperatures ranging from ~450 to 70°C) from the Graubünden region of the Central Alps demonstrate that a pronounced thermal mismatch between the Austroalpine allochthon (Alpine “orogenic lid”) and the Pennine zone persisted until at least 29 Ma and, allowably, until circa 18 Ma. The observed mismatch supports previous suggestions that the famous “overthrust” between the Austroalpine allochthon and the Pennine zone, historically regarded as primarily an Eocene top-north thrust fault, is in fact primarily an Oligocene-Miocene normal fault that has a minimum of 60 km of displacement with top-south or top-southeast sense of shear. Two hallmarks of Alpine geology, deposition of the foredeep Molasse and emplacement of the Helvetic nappes, appear to be coeval, peripheral manifestations of crustal thickening via the interposition of the Pennine zone as a northward intruding wedge between the Austroalpine “lid” and the European cratonic margin, with the Helvetic system (European margin) acting as the “floor” of the wedge. We presume the Penninic wedge is driven by the buoyant rise of subducted crust no longer able to remain attached to the descending slab. If so, emplacement of the Pennine wedge could have occurred mainly after Adria was juxtaposed against cratonic Europe.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77818, title ="Geologic map of the east-central Meadow Valley Mountains, and implications for reconstruction of the Mormon Peak detachment, Nevada", author = "Swanson, E. and Wernicke, B. P.", journal = "Geosphere", volume = "13", number = "4", pages = "1234-1253", month = "August", year = "2017", doi = "10.1130/GES01148.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170530-075528473", note = "© 2017 Geological Society of America. CC-licensed.\n\nReceived 1 October 2014; Revision received 30 November 2016; Accepted 5 April 2017. \n\nThis research was supported by NSF Grant EAR-1250565 awarded to B. Wernicke and J. Eiler, and by the Caltech Tectonics Observatory of the Gordon and Betty Moore Foundation.", revision_no = "13", abstract = "The role of low-angle faults in accommodating extension within the upper crust remains controversial because the existence of these faults markedly defies extant continuum theories of how crustal faults form, and once initiated, how they continue to slip. Accordingly, for many proposed examples, basic kinematic problems like slip direction, dip angle while active, and magnitude of offset are keenly debated. A well-known example is the Miocene Mormon Peak detachment and overlying Mormon Peak allochthon of southern Nevada (USA), whose origin and evolution have been debated for several decades. Here, we use geologic mapping in the Meadow Valley Mountains to help define the geometry and kinematics of emplacement of the Mormon Peak allochthon, the hanging wall of the Mormon Peak detachment. Pre-exten\u00adsion structural markers, inherited from the east-vergent Sevier thrust belt of Meso\u00adzoic age, are well suited to constrain the geometry and kine\u00admatics of the detachment. In this study, we add to these markers a newly mapped Sevier-\u00adage monoclinal flexure preserved in the hanging wall of the detachment. The bounding axial surfaces of the flexure can be readily matched to the base and top of the frontal Sevier thrust ramp, which is exposed in the footwall of the detachment to the east in the Mormon Mountains and Tule Springs Hills. Multiple proxies for the slip direction of the detachment, including the mean tilt direction of hanging wall fault blocks, the trend of striations measured on the fault plane, and other structural features, indicate that it is approximately S77°W (257°). Given the observed structural separation lines between the hanging wall and footwall, this slip direction indicates 12–13 km of horizontal displacement on the detachment (14–15 km net slip), lower than a previous estimate of 20–22 km, which was based on erroneous assumptions in regard to the geometry of the thrust system. Based on a new detailed map compilation of the region and recently published low-temperature thermochronologic data, palinspastic constraints also preclude earlier suggestions that the Mormon Peak allochthon is a composite of diachronously emplaced, surficial landslide deposits. Although earlier suggestions that the initiation angle of the detachment in the central Mormon Mountains is ∼ 20°–25° remain valid, the geometry of the Sevier-age monocline in the Meadow Valley Mountains and other structural data suggest that the initial dip of the detachment steepens toward the north beneath the southernmost Clover Mountains, where the hanging wall includes kilometer-scale accumulations of volcanic and volcaniclastic strata.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/72400, title ="Spatiotemporal evolution of fault slip rates in deforming continents: The case of the Great Basin region, northern Basin and Range province", author = "Pérouse, Eugénie and Wernicke, Brian P.", journal = "Geosphere", volume = "13", number = "1", pages = "112-135", month = "January", year = "2017", doi = "10.1130/GES01295.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161129-104449115", note = "© 2016 Geological Society of America. \n\nReceived 17 November 2015. Revision received 23 September 2016. Accepted 25 October 2016. First Published on November 23, 2016. \n\nWe are grateful to N. Chamot-Rooke, M. Delescluse, J. Davis, M. Fouch, W. Holt, R. Porter, and M. West for useful discussions. We thank the two anonymous reviewers for their valuable comments, which significantly improved the final version of the manuscript. This research was supported by the Earthscope Program of the National Science Foundation (grant EAR-10-53161 to Wernicke).", revision_no = "16", abstract = "Compilation and synthesis of neotectonic data from the Great Basin region (western U.S.), based on 173 published studies for 171 faults across the region, offer an unprecedented view into the spatiotemporal evolution of strain release in continental domains, at time scales of 1 k.y. to 1 m.y. \n\nThe results indicate a mean vertical surface displacement for normal faulting earthquakes of 2 m (approximately two-thirds of events in the 1–3 m range). The distribution of earthquake recurrence intervals is more scattered, with a mode of 1–3 k.y., a mean of 11 k.y., and 15% of recurrence intervals >20 k.y. While strike-slip faults nearest the plate boundary show relatively steady slip rates through time, northern Great Basin normal faults have had marked temporal slip-rate variations in the Quaternary. Since 15 ka, strain release has been concentrated near the margins (fault slip rates to 1–2 mm/yr), with the central region being nearly inactive. However, over the past 150 k.y., finite deformation is more evenly distributed as faults show more uniform slip rates (0.2–0.3 mm/yr) consistent with their long-term rates. The paleo-earthquake distribution since ca. 60 ka shows two kinematic patterns: local clusters (episodes of events repeated on a single fault) and regionally distributed faulting (episodes of events distributed across several parallel faults, each with a single event). We thus propose a model for northern Great Basin normal faults where they alternate between (1) transient fast periods (1–2 mm/yr) lasting ∼50 k.y., characterized by local clusters; and (2) transient slow periods (0.05–0.1 mm/yr) lasting 200–400 k.y., characterized by regional distributed faulting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/67572, title ="The Neotethyan Sanandaj-Sirjan zone of Iran as an archetype for passive margin-arc transitions", author = "Hassanzadeh, Jamshid and Wernicke, Brian P.", journal = "Tectonics", volume = "35", number = "3", pages = "586-621", month = "March", year = "2016", doi = "10.1002/2015TC003926", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160602-092239645", note = "© 2016 American Geophysical Union. \n\nReceived 15 MAY 2015; Accepted 2 FEB 2016; Accepted article online 6 FEB 2016; Published online 11 MAR 2016. \n\nWriting this review paper would not have been possible before the current surge of geochronological data production which started about 10 years ago, referred to in the reference list along with the maps and reports for the region produced by the Geological Survey of Iran. The quality of the presentation was greatly improved by editorial guidance and constructive reviews from Associate Editor A. Khudoley, G. Topuz, and an anonymous reviewer. Mortaza Pirouz is thanked for helping with the ArcGIS compilations of Figures 3 and 7. This work was partially supported by the Caltech Tectonics Observatory under the auspices of Gordon and Betty Moore Foundation and by NSF grant EAR-14-51055 awarded to B. Wernicke.", revision_no = "10", abstract = "The Sanandaj-Sirjan zone of Iran is a northwest trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. The zone contains the most extensive, best preserved record of key events in the formation and evolution of the Neotethys, from its birth in Late Paleozoic time through its demise during the mid-Tertiary collision of Arabia with Eurasia. The record includes rifting of continental fragments off of the northern margin of Gondwanaland, formation of facing passive continental margins, initiation of subduction along the northern margin, and progressive development of a continental magmatic arc. The latter two of these events are critical phases of the Wilson Cycle that, elsewhere in the world, are poorly preserved in the geologic record because of superimposed events. Our new synthesis reaffirms the similarity between this zone and various terranes to the north in Central Iran. Late Paleozoic rifting, preserved as A-type granites and accelerated subsidence, was followed by a phase of pronounced subsidence and shallow marine sedimentation in Permian through Triassic time, marking the formation and evolution of passive margins on both sides of the suture. Subduction and arc magmatism began in latest Triassic/Early Jurassic time, culminating at ~170\u2009Ma. The extinction of arc magmatism in this zone, and its shift northeastward to form the subparallel Urumieh-Dokhtar arc, occurred diachronously along strike, in Late Cretaceous or Paleogene time. Post-Cretaceous uplift transformed the zone from a primarily marine borderland into a marine archipelago that persisted until mid-Tertiary time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/66201, title ="Episodic Dissolution, Precipitation, and Slip along the Heart Mountain Detachment, Wyoming", author = "Swanson, Erika and Wernicke, Brian P.", journal = "Journal of Geology", volume = "124", number = "1", pages = "75-97", month = "January", year = "2016", doi = "10.1086/684253", issn = "0022-1376", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160415-074945846", note = "© 2016 University of Chicago Press.\n\nManuscript received October 31, 2014; accepted September 9,\n2015; electronically published January 8, 2016.\n\nThis research was supported by National Science Foundation grant EAR 12-50565 awarded to B. P. Wernicke and J. Eiler and by the Gordon and Betty Moore Foundation.", revision_no = "11", abstract = "The Heart Mountain allochthon is among the largest landslide masses in the rock record. The basal fault, the Heart Mountain detachment, is an archetype for the mechanical enigma of brittle fracture and subsequent frictional slip on low-angle faults, both of which appear to occur at ratios of shear stress to normal stress far below those predicted by laboratory experiments. The location of the detachment near the base of thick cratonic carbonates, rather than within subjacent shales, is particularly enigmatic for frictional slip. A broad array of potential mechanisms for failure on this rootless fault have been proposed, the majority of which invoke single-event, catastrophic emplacement of the allochthon. Here, we present field, petrographic, and geochemical evidence for multiple slip events, including cross-cutting clastic dikes and multiple brecciation and veining events. Cataclasites along the fault show abundant evidence of pressure solution creep. Banded grains, which have been cited as evidence for catastrophic emplacement, are associated with stylolitic surfaces and alteration textures that suggest formation through the relatively slow processes of dissolution and chemical alteration rather than dynamic suspension in a fluid. Temperatures of formation of fault-related rocks, as revealed by clumped isotope thermometry, are low and incompatible with models of catastrophic emplacement. We propose that displacement along the gently dipping detachment was initiated near the base of the carbonates as localized patches of viscous yielding, engendered by pressure solution. This yielding, which occurred at very low ratios of shear stress to normal stress, induced local subhorizontal tractions along the base of the allochthon, raising shear stress levels (i.e., locally rotating the stress field) to the point where brittle failure and subsequent slip occurred along the detachment. Iteration of this process over geological time produced the observed multikilometer displacements. This concept does not require conditions and materials that are commonly invoked to resolve the stress paradox for low-angle faults, such as near-lithostatic fluid pressures or relative weakness of phyllosilicates in the brittle regime. Cyclic interaction of viscous creep (here by pressure solution) and brittle failure may occur under any fluid pressure conditions and within any rock type, and as such it may be an attractive mechanism for slip on “misoriented” fault planes in general.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36937, title ="The Neoproterozoic Noonday Formation, Death Valley region, California: Reply", author = "Petterson, R. and Prave, A. R.", journal = "Geological Society of America Bulletin", volume = "125", number = "1-2", pages = "252-255", month = "January", year = "2013", doi = "10.1130/B30700.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130215-082128433", note = "© 2013 Geological Society of America. \n\nManuscript received 26 March 2012. Revised manuscript received 18 July 2012. Manuscript accepted 28 July 2012. \n\nWe thank Pavlis for helping to illustrate so strikingly the fact that strain in orogenic belts may be focused into discrete zones. This highlights the necessity to combine careful mapping with geological circumspection in order to minimize the potential for arriving at erroneous, regional-scale conclusions from factually correct, outcrop-scale observations.", revision_no = "11", abstract = "Because our paper was focused on the stratigraphy of the Noonday Formation and the upper part of the underlying Wildrose Diamictite of the Kingston Peak Formation, we did not dwell on the structural geology, beyond presentation of geologic maps and photographs of our measured sections, and description of structural complexities, where appropriate, in our detailed stratigraphic sections in the GSA Data Repository. All metamorphic tectonites, as a definitional matter, are metamorphic rocks, but it is not the case that all metamorphic rocks are tectonites, or that they everywhere absorb large amounts of penetrative strain. We welcome this opportunity to summarize previous work bearing on this issue in Neoproterozoic strata exposed in the central and northern Panamint Range, and present additional photodocumentation demonstrating that our measured stratigraphic sections are structurally intact. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48172, title ="Aerial extent of the coastal drainage system in the wake of the Laramide collapse of the California Arc", author = "Wernicke, Brian", journal = "Abstracts with Programs - Geological Society of America", volume = "44", number = "7", pages = "490", month = "November", year = "2012", issn = "0016-7592", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140807-095156671", note = "© 2012 Geological Society of America.", revision_no = "12", abstract = "Saleeby's (2003, Tectonics) synthesis of the Laramide geology of coastal S California (including fragments of Salinia) suggested the tectonic demise of the forearc and western arc elements, accompanied by the foundering of the E continental arc into a continental borderland that ultimately accumulated 1000s of meters of Maastrichtian to Recent sediments. An important consequence of the formation of this borderland was the expansion of the coastal drainage system. Prior to this time, K foreland deposits in Utah were receiving abundant arc-derived zircon. After the collapse, coastal deposits (esp. middle Eocene to early Miocene Sespe Fm.) began to receive exotic detritus in their gravel fraction, in particular orthoquartzites from at least as far inland as the Mojave and central Arizona regions (Howard, 2000, GSAB). Wernicke et al. (2010, 2012, GSA Abstr.) showed that certain orthoquartzite clasts in the upper part of the Sespe Fm. have a combination of petrographic, geochemical, paleomagnetic and detrital zircon signatures that are unique to the Shinumo Quartzite, a ca. 1.1 Ga orthoquartzite known only from the Upper Granite Gorge region of E Grand Canyon. This discovery corroborates earlier thermochronometric analyses of the Grand Canyon (Flowers et al., 2008, GSAB), and also suggests that (1) E Grand Canyon had already been cut by 20 Ma; (2) a precursor \"Arizona River\" drainage system was supplying detritus to the coastal borderlands; and (3) the post-Laramide drainage divide had locally migrated as far east as the Cordilleran foreland (Wernicke, 2011, GSAB). A commonly cited criticism for this \"Arizona River hypothesis\" is that the detrital zircon signature in the Sespe Fm. and other coastal deposits contain minimal amounts of zircon of Neoprot-Plz age, which is abundant in Upper Plz and Mz sandstones on the Colorado Plateau (e.g. Spafford et al., 2009; UCLA thesis). However, quantitative analyses of the system, considered from the point of view of either the source region or the Sespe Formation itself, predict that the fraction of Neoprot-Plz zircons in the Sespe derived from Grand Canyon to be ca. 0.2 to 0.3%, many times lower than their observed frequency (n = 5/446). This result underscores the importance of per mil-level detrital zircon fractions, which are often dismissed as \"negligible\" or \"virtually zero.\"", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/29239, title ="On seasonal signals in geodetic time series", author = "Davis, James L. and Wernicke, Brian P.", journal = "Journal of Geophysical Research B", volume = "117", pages = "Art. No. B01403 ", month = "January", year = "2012", doi = "10.1029/2011JB008690 ", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120210-114355340", note = "© 2012 by the American Geophysical Union.\n\nReceived 19 July 2011; revised 1 November 2011; accepted 21 November 2011; published 11 January 2012.\nThis work was supported in part by NSF\ngrants EAR-0809195 and EAR-0810328 and NASA grants NNX08AJ79\nand NNX11AB97G. The ZIMM (Zimmerwald) GNSS site is operated by\nthe Swiss Federal Office of Topography. The time series of ZIMM coordinates\nwas obtained from the Scripps Orbit and Permanent Array Center\n(SOPAC). We thank Y. Bock and P. Feng for providing details concerning\nthe SOPAC analysis and R. King for information regarding the impact of\nfirmware changes. The GRACE Level-2 data (Stokes coefficients) used in\nour study were provided by the University of Texas Center for Space\nResearch (CSR) analysis and were retrieved from ftp://podaac.jpl.nasa.gov/allData/grace/. GRACE is a joint partnership between the National\nAeronautics and Space Administration (NASA) in the United States and\nDeutsches Zentrum für Luft- und Raumfahrt (DLR) in Germany. Generic\nMapping Tools (GMT) [Wessel and Smith, 1998] were used to make the\nfigures. We thank M. Kogan and W. Menke for comments on the manuscript.\nT. Parsons (Associate Editor), C. Watson, and an anonymous reviewer provided\nvaluable reviews.", revision_no = "16", abstract = "We explore implications for modeling and noise analysis of stochastic seasonal processes of climatic origin in geodetic time series. Seasonal signals are generally modeled as sinusoids with annual periods (and harmonics thereof), each with constant amplitude and phase. However, environmental noise that underlies the seasonal signal in geodetic time series has a reddened power spectral density (PSD). We investigate the form of the PSD of a time series having a stochastic seasonal component and find that for frequencies greater than the nominal seasonal frequency, the PSD of the time series reflects the PSD of the seasonal amplitudes. For example, if the PSD of the seasonal amplitudes can be expressed as an inverse power law, then the PSD of the time series will behave as an inverse power law for high frequencies. Stochastic seasonal variability will also induce a peak near the nominal seasonal frequency in addition to that of the mean seasonal signal and will be relatively flat below this frequency. It is therefore possible that some of the noise in Global Navigation Satellite Systems (GNSS) time series reported by others may be associated with neglecting the stochastic component of the seasonal signal. We use a GNSS time series from site ZIMM as an example to demonstrate the existence of a variable seasonal signal (without attributing its cause), and we use an example Gravity Recovery and Climate Experiment (GRACE) time series from Alaska to demonstrate that use of a nonstochastic seasonal model can have a significant impact on the value and uncertainty of time-variable rates estimated from the time series. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/31824, title ="Temperatures and fluids on faults based on carbonate clumped–isotope thermometry", author = "Swanson, Erika M. and Wernicke, Brian P.", journal = "American Journal of Science", volume = "312", number = "1", pages = "1-21", month = "January", year = "2012", doi = "10.2475/01.2012.01", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120606-110618419", note = "© 2012 American Journal of Science. \n\nThe clarity of the manuscript was greatly improved by the reviews of Lawford Anderson, Sam Haines, and an anonymous reviewer. This research was supported by NSF Grant EAR-0911772, and by the Gordon and Betty Moore Foundation. Tectonics Observatory contribution no. 168.", revision_no = "15", abstract = "We present results from a carbonate clumped-isotope thermometric study of 42 carbonate samples collected within ∼1 m or less of the Mormon Peak detachment, a large-slip Miocene normal fault in the Basin and Range province of southern Nevada. Samples include cataclastic rocks, narrow vein fillings and larger void-filling carbonates. Our results are consistent with earlier measurements of O and C isotopic ratios and fluid inclusion temperatures, and provide independent constraints on the isotopic composition and temperature of both syntectonic and post-tectonic pore waters. The results reveal a wide range of precipitation temperatures (24 to 137 °C) associated with deformation, and indicate that the pore waters were meteoric, with δ^(18)O as low as −11.6 permil (VSMOW) and δ^(13)C as low as −8.0 permil (VPDB). The results do not provide any direct evidence for high-temperature thermal decarbonation reactions (∼500 to 800 °C) that are widely expected to result from flash heating along upper crustal faults, although they do not rule them out so long as recarbonation occurs at very low temperature, or the products of these reactions are volumetrically minor. The results are difficult to reconcile with recent suggestions that the detachment is the base of one or more catastrophically emplaced, surficial landslides. In concert with other lines of evidence, the data are most simply interpreted as recording deformation and precipitation events through a long history of slip, accompanied by relatively deep (>3 km) circulation of meteoric pore waters along the detachment plane.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/27663, title ="Use of Clumped-Isotope Thermometry To Constrain the Crystallization Temperature of Diagenetic Calcite", author = "Huntington, Katharine W. and Budd, David A.", journal = "Journal of Sedimentary Research", volume = "81", number = "9-10", pages = "656-669", month = "September", year = "2011", doi = "10.2110/jsr.2011.51 ", issn = "1527-1404", url = "https://resolver.caltech.edu/CaltechAUTHORS:20111108-073305297", note = "© 2011 SEPM Society for Sedimentary Geology. \n\nReceived 2 December 2010; accepted 16 April 2011. \n\nThis work was supported by National Science Foundation grant EAR-0610115 and the Caltech Tectonics Observatory. Acknowledgment is made to the donors of the American Chemical Society Petroleum Research Fund for support of this research (ACS-PRF grant 49709 to KWH). We thank reviewers Peter Eichhubl and Stefano Bernasconi, editor Gene Rankey, and associate editor Leslie Melim for helpful reviews. We are grateful to R.A. Young for access to his sample archive and field observations, to G.R. Rossman for assistance with Fourier transform infrared spectroscopy, to J. Harnmeijer and B.C. Schreiber for assistance with microscopy, and to R.M. Flowers, S. Bergman, and O. Bachmann for discussions that improved the paper. ", revision_no = "15", abstract = "We describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped-isotope thermometry, a paleothermometer based on the ^(13)C–^(18)O-bond enrichment in carbonates. Application of this thermometer to calcified gastropod shells and calcite cements in an early Eocene limestone from the Colorado Plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123°C. The early Eocene host sediments were never deeply buried, but they experienced a significant thermal pulse associated with the emplacement of a late Miocene basalt flow. The combination of independent constraints on thermal history with clumped-isotope thermometry, petrographic (including cathodoluminescence) observations, and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources. The petrography and calcite δ^(18)O values, taken alone, suggest that the aragonite-to-calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample. However, addition of clumped-isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94–123°C in a highly rock-buffered microenvironment (i.e., with the isotopic composition of fluid buffered by coexisting carbonate), millions of years after lithification of the matrix and formation of initial low-temperature (14–19°C) calcite cements within shell body cavities. Clumped-isotope temperatures in excess of reasonable Earth-surface conditions recorded by later-formed cements demand that cement growth occurred in association with the lava emplacement. Our results illustrate the potential for clumped-isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable-isotopic and petrographic data alone, and demonstrate how petrographic characterization of clumped-isotope thermometry samples can benefit paleoclimate studies.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24167, title ="The California River and its role in carving Grand Canyon", author = "Wernicke, Brian", journal = "Geological Society of America Bulletin", volume = "123", number = "7-8", pages = "1288-1316", month = "July", year = "2011", doi = "10.1130/B30274.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110622-115344807", note = "© 2011 Geological Society of America. \n\nReceived 16 February 2010; Revision received 6 May 2010; Accepted 28 June 2010. First published online January 26, 2011. \n\nThe late Don Elston first introduced me to the concept\nof a Cretaceous age for Grand Canyon. I am also grateful to J.M. Eiler, K.A. Farley, R.M. Flowers, K.W. Huntington, J.B. Saleeby, and R.A. Young for discussions that prompted this synthesis, and to S.J. Davis, W.R. Dickinson, M. Grove, R.V. Ingersoll, and J.E. Spencer for sharing detrital zircon data prior to publication. I thank K.A. Farley and J. Harvey for assistance with the RDAAM model and using the HeFTy software. The presentation was greatly improved from the careful and constructive reviews of S.M. Cather, R.V. Ingersoll, K.E. Karlstrom, P.K. Link, J. Pederson, J.D. Walker, and R.A. Young, although responsibility\nfor errors in either fact or interpretation rest solely\nwith the author. Figure 13 was drafted by J. Mayne.\nThis research was funded by National Science Foundation\ngrant EAR-0810324 and the Gordon and Betty Moore Foundation (Tectonics Obervatory Cont. #143).", revision_no = "14", abstract = "Recently published thermochronological and paleoelevation studies in the Grand Canyon region, combined with sedimentary provenance data in both the coastal and interior portions of the North American Cordillera, place important new constraints on the paleohydrological evolution of the southwestern United States. Review and synthesis of these data lead to an interpretation where incision of a large canyon from a plain of low elevation and relief to a canyon of roughly the length and depth of modern Grand Canyon occurred primarily in Campanian time (80–70 Ma). Incision was accomplished by a main-stem, NE-flowing antecedent river with headwaters on the NE slope of the North American Cordillera in California, referred to herein after its source region as the California River. At this time, the river had cut to within a few hundred meters of its modern erosion level in western Grand Canyon, and to the level of Lower Mesozoic strata in eastern Grand Canyon. Subsequent collapse of the headwaters region into a continental borderland and coeval uplift of the Cordilleran foreland during the Laramide orogeny reversed the river's course by Paleogene time. After reversal, its terminus lay near its former source regions in what is now the Western Transverse Ranges and Salinian terrane. Its headwaters lay in the ancient Mojave/Mogollon Highlands region of Arizona and eastern California, apparently reaching as far northeast as the eastern Grand Canyon region. This system is herein referred to after its source region as the Arizona River. From Paleogene through late Miocene time, the interior of the Colorado Plateau was a closed basin separated from the Arizona River drainage by an asymmetrical divide in the Lees Ferry–Glen Canyon area, with a steep SW flank and gently sloping NE flank that drained into large interior lakes, fed primarily by Cordilleran/Rocky Mountain sources to the north and west, and by recycled California River detritus shed from Laramide uplifts on the plateau. By Oligocene time, the lakes had largely dried up and were replaced by ergs. By mid-Miocene time, a pulse of unroofing had lowered the erosion level of eastern Grand Canyon to within a few hundred meters of its present level, and the Arizona River drainage below modern Grand Canyon was deranged by extensional tectonism, cutting off the supply of interior detritus to the coast. Increasing moisture in the Rocky Mountains in late Miocene time reinvigorated fluviolacustrine aggradation NE of the asymmetrical divide, which was finally overtopped between 6 and 5 Ma, lowering base level in the interior of the plateau by 1500 m. This event reintegrated the former Arizona drainage system through a cascade of spillover events through Basin and Range valleys, for the first time connecting sediment sources in Colorado with the coast. This event, combined with the intensification of summer rainfall as the Gulf of California opened, increased the sediment yield through Grand Canyon by perhaps two orders of magnitude from its Miocene nadir, giving birth to the modern subcontinental-scale Colorado River drainage system. The Colorado River has thus played a major role in unroofing the interior of the Colorado Plateau, but was not an important factor in the excavation of Grand Canyon.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24155, title ="The Neoproterozoic Noonday Formation, Death Valley region, California", author = "Petterson, R. and Prave, A. R.", journal = "Geological Society of America Bulletin", volume = "123", number = "7-8", pages = "1317-1336", month = "July", year = "2011", doi = "10.1130/B30281.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110621-115845037", note = "© 2011 Geological Society of America. \n\nReceived 22 February 2010; Revision received 6 August 2010;\nAccepted 9 August 2010. First published online February 11, 2011. \n\nWe thank F. Corsetti for a thorough, thoughtful review and an anonymous reviewer; their combined comments much improved this manuscript. Field work was supported by National Science Foundation (NSF) grant EAR-0107123 and EAR-0310413 to Wernicke and by grants from The Carnegie Trust for The Universities of Scotland and The Russell Trust to Prave and Fallick.", revision_no = "15", abstract = "The Neoproterozoic–Cambrian succession in the Death Valley region of the southwestern United States is among the best exposed and easily accessible in the world. The largest single exposure of these strata occurs in the Panamint Range on the west side of Death Valley, and it, although variably metamorphosed, contains the most complete sections of the Noonday Formation cap carbonate sequence. New geological mapping, measured sections, and high-resolution carbon isotope data for the Noonday Formation in this range enable establishment of a unified stratigraphy across the Death Valley region that consists of three units. From the base upward, they include: the Sentinel Peak Member of light-gray, massive to laminated fine dolostone locally containing vugs and tubes variably filled with micrite, spar, or quartz (and rarely galena), and varying from 2 to 200 m in thickness; the Radcliff Member, composed of feldspathic shale and sandstone and thin-bedded limestone, 0–200 m thick; and the newly defined Mahogany Flats Member of gray, commonly stromatolitic, thin- to medium-bedded fine dolostone that is ~200 m thick at its type locality.\n\nCarbon isotopic trends in the Panamint Range match to within 1‰–2‰ reproducibility those known for the equivalent nonmetamorphosed strata in the eastern Death Valley sections. A composite section of the Noonday Formation displays a chemostratigraphic profile with values near −3‰ through the cap dolostone of the Sentinel Peak Member, a decline to −6‰ in the lower part of the Radcliff Member, followed by a recovery to near 0‰ and subsequent decline toward −2‰ in the remainder of the Radcliff units and lower Mahogany Flats Member, and then a return to positive values (4‰) through the remainder of the Mahogany Flats Member. This pattern matches the Ediacaran cap carbonate in Namibia remarkably well, and, assuming our carbon isotopic correlations are correct, it indicates that Noonday deposition occurred at the beginning of the Ediacaran Period, and that the immediately underlying Wildrose Diamictite of the Kingston Peak Formation probably represents the younger Cryogenian (Marinoan) glacial episode. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24156, title ="The Shuram and subsequent Ediacaran carbon isotope excursions from southwest Laurentia, and implications for environmental stability during the metazoan radiation", author = "Verdel, Charles and Wernicke, Brian P.", journal = "Geological Society of America Bulletin", volume = "123", number = "7-8", pages = "1539-1559", month = "July", year = "2011", doi = "10.1130/B30369.1 ", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110621-115909544", note = "© 2011 Geological Society of America. \n\nReceived 8 July 2010; Revision received 10 October 2010;\nAccepted 12 October 2010. First published online February 11, 2011. \n\nThis study benefited from discussions with Ryan\nPetterson, John Grotzinger, David Fike, John Eiler,\nand Craig Hebert. We thank David Mucciarone at\nthe Stanford University Stable Isotope Laboratory\nand Lora Wingate at the University of Michigan\nStable Isotope Laboratory for conducting C and O\nisotope analyses. This research was supported by National\nScience Foundation grants EAR-0107123 and\nEAR-0310413.", revision_no = "16", abstract = "Current understanding of secular changes in the carbon isotopic composition of mid- to late Ediacaran carbonates suggests a relatively long, steady recovery of the global ocean from the Shuram negative excursion, followed by a smaller negative excursion at the Precambrian-Cambrian boundary. New radiometric, stratigraphic, and carbon isotope data from thick exposures of the upper Johnnie Formation in the Panamint Range of eastern California, combined with data from carbonate-rich facies of the Stirling Quartzite in the Funeral Mountains, confirm an Ediacaran age for these strata and provide a more complete record of isotopic variations during this time interval than previously determined from SW Laurentia and other key sections around the globe. A siltstone in the lower part of the Johnnie Formation yielded a detrital zircon grain with an age of 640.33 ± 0.09 Ma, lowering the maximum radiometric age constraint on the Johnnie Formation by >400 m.y., consistent with an Ediacaran age based on chemo- and biostratigraphic data. In contrast to previous C isotope compilations from this region, which were generally based on relatively thin portions of the Cordilleran miogeocline near its depositional hinge, the more basinward exposures exhibit a recovery from values near –12‰ to 0‰ within the upper part of the Johnnie Formation. Details in the shape of the chemostratigraphic profile through the upper Johnnie Formation closely match those in profiles through the Wonoka Formation in South Australia (which lies above the basal Ediacaran global stratotype section and point) and the Shuram-Buah interval in Oman, confirming temporal correlation and suggesting genesis through changes in the isotopic composition of the global ocean. The Shuram excursion in SW Laurentia is followed by at least three smaller Ediacaran to earliest Cambrian isotopic excursions recorded within, from oldest to youngest, the uppermost Johnnie Formation, the middle Stirling Quartzite, and the lower Wood Canyon Formation. These data indicate that the negative excursion associated with the base of the Cambrian is not a unique post-Shuram event, and that post-Shuram, pre-Cambrian animal evolution occurred in an environment of repeated large-magnitude fluctuations in the carbon isotopic composition of the global ocean.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24386, title ="A Paleogene extensional arc flare-up in Iran\n\n", author = "Verdel, Charles and Wernicke, Brian P.", journal = "Tectonics", volume = "30", pages = "Art. No. TC3008 ", month = "June", year = "2011", doi = "10.1029/2010TC002809", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110712-132640320", note = "© 2011 American Geophysical Union. \n\nReceived 8 October 2010; revised 16 February 2011; accepted 2 March 2011; published 22 June 2011. \n\nWe acknowledge analytical assistance from Axel Schmitt of the UCLA Keck ion microprobe facility, Terry Spell of the Nevada Isotope Geochronology Lab, and Mike Rhodes of the University of Massachusetts. This research was supported by NSF grant EAR‐0511054 awarded to B. Wernicke, grant EAR‐0337775 awarded to G. Axen and B. Horton, and the Gordon and Betty Moore Foundation. The ion microprobe facility at UCLA is partly supported by a grant from the Instrumentation and Facilities Program, Division of Earth Sciences, National Science Foundation. Discussions with Gary Axen, John Eiler, Jahandar Ramezani, and Danny Stockli contributed significantly to the development of ideas in this paper. We appreciate constructive reviews from Philippe Agard, Mihai Ducea, Robert Miller, Chris Morley, and an anonymous reviewer. This is Caltech Tectonics Observatory contribution 148.", revision_no = "31", abstract = "Arc volcanism across Iran is dominated by a Paleogene pulse, despite protracted and presumably continuous subduction along the northern margin of the Neotethyan ocean for most of Mesozoic and Cenozoic time. New U-Pb and ^(40)Ar/^(39)Ar data from volcanic arcs in central and northern Iran constrain the duration of the pulse to ~17 Myr, roughly 10% of the total duration of arc magmatism. Late Paleocene-Eocene volcanic rocks erupted during this flare-up have major and trace element characteristics that are typical of continental arc magmatism, whereas the chemical composition of limited Oligocene basalts in the Urumieh-Dokhtar belt and the Alborz Mountains which were erupted after the flare-up ended are more consistent with derivation from the asthenosphere. Together with the recent recognition of Eocene metamorphic core complexes in central and east central Iran, stratigraphic evidence of Eocene subsidence, and descriptions of Paleogene normal faulting, these geochemical and geochronological data suggest that the late Paleocene-Eocene magmatic flare-up was extension related. We propose a tectonic model that attributes the flare-up to decompression melting of lithospheric mantle hydrated by slab-derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. We suggest that Paleogene magmatism and extension was driven by an episode of slab retreat or slab rollback following a Cretaceous period of flat slab subduction, analogous to the Laramide and post-Laramide evolution of the western United States. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39797, title ="Hot summers in the Western United States during the Late Cretaceous and Early Cenozoic", author = "Snell, Kathryn E. and Thompson, Jeffrey", journal = "Mineralogical Magazine", volume = "75", number = "3", pages = "1901-1901", month = "June", year = "2011", issn = "0026-461X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130807-084226862", note = "© 2011 by the Mineralogical Society of Great Britain and Ireland.\n\nOpen Access Article.\n\nPublished online 1 August 2011.\n\n", revision_no = "11", abstract = "Understanding how seasonal temperatures on land respond to global greenhouse climate conditions is important for\npredicting effects of climate change on ecosystem structure, agriculture and distributions of natural resources. Fossil floral\nand faunal assemblages suggest winter temperatures in middle and high latitude continental interiors during the Cretaceous\nand early Cenozoic were at or above freezing, whereas terrestrial summer temperature estimates are uncertain.\nCarbonate clumped isotope (Δ_(47)) temperature estimates from lacustrine and paleosol carbonates appear to be generally\nbiased toward summer temperatures in middle and high latitudes. Though problematic for reconstructing mean annual\ntemperature (MAT), this bias presents an opportunity to reconstruct terrestrial summer temperatures and, through\ncomparison with paleobotanical data, estimate past terrestrial seasonality.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/23347, title ="Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet", author = "Copley, Alex and Avouac, Jean-Philippe", journal = "Nature", volume = "472", number = "7341", pages = "79-81", month = "April", year = "2011", doi = "10.1038/nature09926", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110415-142614838", note = "© 2011 Nature Publishing Group, a division of Macmillan Publishers Limited. \n\nReceived 24 September 2010; accepted 10 February 2011.\nPublished online06 April 2011. \n\nWe thank the Gordon and Betty Moore Foundation for support\nthrough the Caltech Tectonics Observatory, and Pembroke College in the University of Cambridge for financial support to A.C. This work benefited from a review by L. Flesch. This is Caltech Tectonics Observatory contribution number 145.\n\nAuthor Contributions: A.C. performed the calculations, A.C., J.-P.A. and B.W. discussed the results, and A.C. and J.-P.A. wrote the manuscript.", revision_no = "24", abstract = "How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The upper crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the upper crust of southern Tibet and the underthrusting Indian crust. Such coupling is inconsistent with the presence of active ‘channel flow’ beneath southern Tibet, and suggests that the Indian crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20059, title ="Detecting Large-scale Intracontinental Slow-slip Events (SSEs) Using Geodograms", author = "Wernicke, Brian and Davis, James L.", journal = "Seismological Research Letters", volume = "81", number = "5", pages = "694-698", month = "September", year = "2010", doi = "10.1785/gssrl.81.5.694", issn = "0895-0695", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100921-090041434", note = "© 2010 Seismological Society of America. \n\nThis research was supported by NSF Grants EAR-0810328 (BW) and EAR-0809195 (JLD), and by the Caltech Tectonics Observatory. We are grateful to D. L. Anderson and D. J. Stevenson for alerting us to the TBO as a plausible origin of the quasi-biennial signal on the geodogram.", revision_no = "18", abstract = "Since the advent in the 1980s of GPS networks to monitor crustal velocity fields, interpretations of geodetic data have generally been based on maps of Earth's surface showing average horizontal site velocity over a specified period of time and plots showing velocity gradients as a function of a position coordinate (e.g., Donnellan et al. 1993; Bennett et al. 1999). For continuous networks, these plots are typically supplemented by time series of position in order to assess the importance of time-dependent or transient behavior (Bock et al. 1993; Hudnut et al. 2002). Thus far, regional transient motions have been revealed by plotting position time series from multiple sites on a common time axis. These plots have been effective in demonstrating the existence of slow-slip events (SSEs) on subduction megathrust interfaces around the globe (e.g., Miller et al. 2002; Melbourne et al. 2005; Schwartz and Rokosky 2007). A large-scale intraplate SSE in the northern Basin and Range Province that occurred between 1999 and 2005 was initially identified by plotting continuous time series with a vertical time axis, arranged according to a spatial position coordinate for each site (Davis et al. 2006, their Figure 3A).\nBecause transient motions are by definition changes in velocity, however, the spatial coherence and magnitude of velocity changes are most directly addressed by plotting the time dependence of velocity rather than position. Here, we describe a method for calculating velocity time series, and then we use these to construct a \"geodogram\" from raw continuous GPS time series. The new time series reveal additional transient motions from 2005 to 2007 that are interpreted to reflect the onset of a new SSE beginning in late 2006.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/18812, title ="Influence of climate change and uplift on Colorado Plateau paleotemperatures from carbonate clumped isotope thermometry", author = "Huntington, K. W. and Wernicke, B. P.", journal = "Tectonics", volume = "29", pages = "Art. No. TC3005 ", month = "May", year = "2010", doi = "10.1029/2009TC002449 ", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100625-090625683", note = "© 2010 American Geophysical Union. \n\nReceived 21 January 2009; revised 17 August 2009; accepted 28 December 2009; published 25 May 2010. \n\nThis research was supported by National Science Foundation grants EAR‐0610115 and EAR‐0810824 and the Division of Geological and Planetary Sciences at the California Institute of Technology. This manuscript benefited from discussions with Gerard Roe and Tapio Schneider and was improved by thoughtful reviews by Brian Currie, Andreas Mulch, and Paul Kapp. We thank Jon Patchett, Dick Young, and Lesleigh Anderson, who provided many of the samples for which we report data, and Geoff Huntington for assistance in the field.", revision_no = "13", abstract = "The elevation history of Earth's surface is key to understanding the geodynamic processes responsible for the rise of plateaus. We investigate the timing of Colorado Plateau uplift by estimating depositional temperatures of Tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry (a measure of the temperature-dependent enrichment of ^(13)C-^(18)O bonds in carbonates). Comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau. Analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern United States reveals a lake water carbonate temperature (LCT) lapse rate of 4.2 ± 0.6°C/km. Analysis of Miocene deposits from 88 to 1900 m elevation in the Colorado River drainage suggests that the ancient LCT lapse rate was 4.1 ± 0.7°C/km, and temperatures were 7.7 ± 2.0°C warmer at any one elevation than predicted by the modern trend. The inferred cooling is plausible in light of Pliocene temperature estimates off the coast of California, and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 Ma. Together with previous paleorelief estimates from apatite (U-Th)/He data from the Grand Canyon, our results suggest most or all of the plateau's lithospheric buoyancy was acquired ∼80–60 Ma and do not support explanations that ascribe most plateau uplift to Oligocene or younger disposal of either the Farallon or North American mantle lithosphere. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/17598, title ="Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan glacial deposits", author = "Mahan, K. H. and Wernicke, B. P.", journal = "Earth and Planetary Science Letters", volume = "289", number = "1-2", pages = "76-86", month = "January", year = "2010", doi = "10.1016/j.epsl.2009.10.031", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100225-130935237", note = "© 2009 Elsevier B.V. \n\nReceived 24 February 2009; revised 29 July 2009; accepted 22 October 2009. Editor: P. DeMenocal. Available online 20 November 2009. \n\nThis research was supported by NSF grants EAR-0107123 and EAR-0310413. The authors express thanks to Tim Raub, Ryan Petterson and Tony Prave for assistance in the field, and to G. Halverson and two anonymous referees for constructive remarks that significantly improved the clarity of the presentation.", revision_no = "15", abstract = "The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan glacial deposits. The litho- and chemo-stratigraphy of these deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited. We report results of in situ Th–U–total Pb (electron microprobe) dating of detrital and authigenic monazite in two samples from the Umberatana Group (Sturtian Holowilena Ironstone and pre-Marinoan Enorama Shale) in the Central Flinders Ranges. Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from 1600 Ma to 760 Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from 680 Ma to 500 Ma. The date of 680 ± 23 Ma (2σ) for the earliest generation of authigenic monazite in sandstone from the Enorama Shale (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan glacial deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian glacial deposits, and (3) supports proposed correlations between type Marinoan deposits and precisely dated glacial deposits in Namibia and China, which bracket the presumed Marinoan equivalents between 655 and 635 Ma. This age is inconsistent with a Re–Os isochron age of 643 ± 2.4 Ma (2σ) on shales near the bottom of the Sturtian–Marinoan interglacial succession, stratigraphically > 3000 m below the Enorama Shale sample, and militate against the hypothesis that the type Marinoan is correlative with the 580 Ma Gaskiers glaciation. Monazite growth near 600 Ma and again at about 500 Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.\n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/17044, title ="Low-temperature thermochronologic constraints on the kinematic history and spatial extent of the Eastern California shear zone", author = "Mahan, K. H. and Guest, B.", journal = "Geosphere", volume = "5", number = "6", pages = "483-495", month = "December", year = "2009", doi = "10.1130/GES00226.1 ", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100104-093728049", note = "© 2009 Geological Society of America. \n\nManuscript received 20 January 2009. Revised manuscript received 20 August 2009. Manuscript accepted 15 September 2009. \n\nThis research was supported by U.S. Department of Energy contract FC-08-98NV12081 to Wernicke. We thank Ken Farley for access to his helium lab for the analytical work. Lindsey Hedges and Becky Flowers helped immensely in the sample preparation and analysis and their efforts are greatly appreciated. \n\nWe are grateful to M. Oskin and T. Wawrzyniec for critical reviews that helped to signifi cantly improve the presentation. Stereonets plotted with Stereonet 6.3 by R.W. Allmendinger.", revision_no = "13", abstract = "The Stateline fault system is a 200-km-long zone of active right-lateral shear along the California-Nevada border, United States. Recent identification of 30 ± 4 km of dextral offset since 13.1 Ma on the southern segment of the fault requires significant displacement to extend farther south than has been commonly considered in the past. However, major structures exposed where the fault projects to the south reveal predominantly dip-slip extensional faulting, suggesting that displacement is transferred into substantial northwest-oriented extension in eastern Ivanpah Valley. New (U-Th)/He apatite data from Proterozoic orthogneiss in the southern McCullough Range and northern New York Mountains support this model by recording dates as young as 5 ± 1 Ma in the structurally deepest parts of the footwalls to the range-bounding normal faults. This age is distinctly younger than both the ages of regional extension in surrounding areas and the youngest (U-Th)/He apatite dates reported from the immediately adjacent Colorado River extensional corridor. Late Miocene–Pliocene extension in Ivanpah Valley, contemporaneous with that elsewhere in the Eastern California shear zone, provides an independent line of support that the eastern margin of the Eastern California shear zone extends to the California-Nevada border. If this age marks the onset of deformation on the State-line system, then long-term slip rates on the southern segment may be as high as 5 mm/yr, significantly higher than the present-day estimate of 0.9 mm/yr derived from geodetic observations across the northern segment of this fault system.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/16806, title ="Characterization of site-specific GPS errors using a short-baseline network of braced monuments at Yucca Mountain, southern Nevada", author = "Hill, Emma M. and Davis, James L.", journal = "Journal of Geophysical Research B", volume = "114", pages = "Art. No. B11402", month = "November", year = "2009", doi = "10.1029/2008JB006027 ", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20091125-094838297", note = "© 2009 American Geophysical Union. \n\nReceived 21 August 2008; accepted 4 August 2009; published 5 November 2009. \n\nThis work was funded by the U.S. Department of Energy, and NSF grants EAR-0346147, EAR-0135457, EAR-0809195, and EAR-0810328. UNAVCO, Inc. supports BARGEN site operation and maintenance. Bob King (MIT) was, as always, extremely gracious with his assistance and advice regarding the GAMIT software. We are also grateful to Jeff Behr (Orion Monitoring Systems, Inc.) for providing technical assistance and detailed station information from the field and to two anonymous reviewers whose insightful comments significantly improved the quality of this manuscript.", revision_no = "12", abstract = "We use a short-baseline network of braced monuments to investigate site-specific GPS effects. The network has baseline lengths of ∼10, 100, and 1000 m. Baseline time series have root mean square (RMS) residuals, about a model for the seasonal cycle, of 0.05–0.24 mm for the horizontal components and 0.20–0.72 mm for the radial. Seasonal cycles occur, with amplitudes of 0.04–0.60 mm, even for the horizontal components and even for the shortest baselines. For many time series these lag seasonal cycles in local temperature measurements by 23–43 days. This could suggest that they are related to bedrock thermal expansion. Both shorter-period signals and seasonal cycles for shorter baselines to REP2, the one short-braced monument in our network, are correlated with temperature, with no lag time. Differences between REP2 and the other stations, which are deep-braced, should reflect processes occurring in the upper few meters of the ground. These correlations may be related to thermal expansion of these upper ground layers, and/or thermal expansion of the monuments themselves. Even over these short distances we see a systematic increase in RMS values with increasing baseline length. This, and the low RMS levels, suggests that site-specific effects are unlikely to be the limiting factor in the use of similar GPS sites for geophysical investigations. \n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86102, title ="Testing the Extensional Detachment Paradigm: A Borehole Observatory in the Sevier Desert Basin", author = "Christie-Blick, Nicholas and Anders, Mark H.", journal = "Scientific Drilling", volume = "8", pages = "57-59", month = "September", year = "2009", doi = "10.2204/iodp.sd.8.09.2009", issn = "1816-3459", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180427-155654592", note = "© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nWe thank ICDP for sponsoring the workshop, the Utah Geological Survey for logistical assistance, and all of the participants for stimulating discussions.", revision_no = "8", abstract = "Low-angle normal faults or detachments are widely regarded as playing an important role in crustal extension and the development of rifted continental margins (Manatschal et al., 2007). However, no consensus exists on how to resolve the mechanical paradox implied by the gentle dips of these faults and by the general absence of evidence for associated seismicity (Sibson, 1985; Wernicke, 1995; Axen, 2004). As part of a new initiative to rationalize geological and geophysical evidence and our theoretical understanding of how rocks deform, a group of forty-seven scientists and drilling experts from five countries met for four days on 15–18 July 2008 to discuss the present status of the paradox and a borehole-based strategy for resolving it. The workshop was held at two venues in Utah (the Utah Department of Natural Resources in Salt Lake City, and Solitude Mountain Resort in the adjacent Wasatch Range), with a one-day field trip to the Sevier Desert basin of west-central Utah (Figs. 1, 2) to examine the general setting of potential drill sites and the footwall geology of the Sevier Desert detachment (Canyon Range).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/12766, title ="Active megadetachment beneath the western United States", author = "Wernicke, Brian and Davis, James L.", journal = "Journal of Geophysical Research B", volume = "113", number = "B11", pages = "B11409", month = "November", year = "2008", doi = "10.1029/2007JB005375", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:WERjgrb08", note = "© 2008. American Geophysical Union. \n\nReceived 6 September 2007; revised 21 March 2008; accepted 14 August 2008; published 21 November 2008. \n\nThis research was supported by National Science Foundation grant EAR-04-53975, DOE cooperative agreement DE-FC28-03RW12232 (Task 3), and the Caltech Tectonics Observatory. Geodetic sites were constructed with technical assistance from the University NAVSTAR Consortium (UNAVCO) facility. The time series for site KTBW were obtained from the PANGA Data Analysis Facility Web site (http://www.panga.cwu.edu/). The time series for site ACAP were obtained from K. Larson. We are grateful to S. Klemperer for prepublication copies of seismic imaging studies in the northern Great Basin and G. Dumond and M. Williams for permission to discuss unpublished data from the Snowbird tectonic zone. We thank Associate Editor W. Schellart and formal reviewers W. Hammomd, P. England, and S. Wesnousky for comments that substantially improved the presentation. We also thank S. Kidder and D. Anderson for comments on an early draft of the manuscript and M. Simons, M. Gurnis, J. Saleeby, and D. Helmberger for useful discussions.", revision_no = "16", abstract = "Geodetic data, interpreted in light of seismic imaging, seismicity, xenolith studies, and the late Quaternary geologic history of the northern Great Basin, suggest that a subcontinental-scale extensional detachment is localized near the Moho. To first order, seismic yielding in the upper crust at any given latitude in this region occurs via an M7 earthquake every 100 years. Here we develop the hypothesis that since 1996, the region has undergone a cycle of strain accumulation and release similar to “slow slip events” observed on subduction megathrusts, but yielding occurred on a subhorizontal surface 5–10 times larger in the slip direction, and at temperatures >800°C. Net slip was variable, ranging from 5 to 10 mm over most of the region. Strain energy with moment magnitude equivalent to an M7 earthquake was released along this “megadetachment,” primarily between 2000.0 and 2005.5. Slip initiated in late 1998 to mid-1999 in northeastern Nevada and is best expressed in late 2003 during a magma injection event at Moho depth beneath the Sierra Nevada, accompanied by more rapid eastward relative displacement across the entire region. The event ended in the east at 2004.0 and in the remainder of the network at about 2005.5. Strain energy thus appears to have been transmitted from the Cordilleran interior toward the plate boundary, from high gravitational potential to low, via yielding on the megadetachment. The size and kinematic function of the proposed structure, in light of various proxies for lithospheric thickness, imply that the subcrustal lithosphere beneath Nevada is a strong, thin plate, even though it resides in a high heat flow tectonic regime. A strong lowermost crust and upper mantle is consistent with patterns of postseismic relaxation in the southern Great Basin, deformation microstructures and low water content in dunite xenoliths in young lavas in central Nevada, and high-temperature microstructures in analog surface exposures of deformed lower crust. Large-scale decoupling between crust and upper mantle is consistent with the broad distribution of strain in the upper crust versus the more localized distribution in the subcrustal lithosphere, as inferred by such proxies as low P wave velocity and mafic magmatism.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39604, title ="Temperature and timing of diagenesis from carbonate clumped isotope thermometry and thermochronology", author = "Huntington, Katharine W. and Wernicke, Brian P.", journal = "Geochimica et Cosmochimica Acta", volume = "72", number = "12", pages = "A403", month = "July", year = "2008", doi = "10.1016/j.gca.2008.05.011", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130726-082611180", note = "© 2008 Published by Elsevier Ltd.", revision_no = "12", abstract = "Temperatures of diagenesis in sedimentary basins are\ncommonly inferred from tools that can constrain rock thermal\nhistories or peak temperatures, but not the timing or\ntemperature of crystal growth for major diagenetic phases. We\ndemonstrate a technique to resolve both the temperature and\ntiming of growth for distinct cementation, re-rystallization,\nand replacement phases using ‘clumped isotope’\npaleothermometry–a new tool based on measurement of the\n^(13)C-^(18)O bond enrichment in carbonates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20781, title ="Unroofing, incision, and uplift history of the southwestern Colorado Plateau from apatite (U-Th)/He thermochronometry", author = "Flowers, R. M. and Wernicke, B. P.", journal = "Geological Society of America Bulletin", volume = "120", number = "5-6", pages = "571-587", month = "May", year = "2008", doi = "10.1130/B26231.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101112-143409190", note = "© 2008 Geological Society of America. \n\nManuscript received 23 March 2007; Revised manuscript received 9 September 2007; Manuscript accepted 17 October 2007. \n\nWe thank Dick Young and Andre Potochnik for insightful discussions and for sharing their extensive knowledge of the geology of the southwestern Colorado Plateau. Sam Bowring and Lee Silver generously provided mineral separates for several samples of Proterozoic basement from the Grand Canyon for which we report data. We thank Karl Karlstrom for the opportunity to collect additional basement samples on the University of New Mexico Grand Canyon River trip. \n \nAssociate Editor Frank Pazzaglia and two anonymous referees provided invaluable advice on improving the presentation of both thermochronometric data and its implications for landscape development in the southwestern plateau region. This research was supported by National Science Foundation grants EAR-0610115 and EAR-0408526 and by the California Institute of Technology Tectonics Observatory.", revision_no = "20", abstract = "The source of buoyancy for the uplift of cratonic plateaus is a fundamental question in continental dynamics. The ~1.9 km uplift of the Colorado Plateau since the Late Cretaceous is a prime example of this problem. We used apatite (U-Th)/He thermochronometry (230 analyses; 36 samples) to provide the first single-system, regional-scale proxy for the unroofing history of the southwestern quadrant of the plateau. The results confirm overall southwest to northeast unroofing, from plateau margin to plateau interior. A single phase of unroofing along the plateau margin in Late Cretaceous to Early Tertiary (Sevier- Laramide) time contrasts with multiphase unroofing of the southwestern plateau interior in Early and mid- to Late Tertiary time. The Early Cretaceous was characterized by northeastward tilting and regional erosion, followed by aggradation of ≥1500 m of Upper Cretaceous sediments along the eroded plateau margin. Sevier-Laramide denudation affected the entire southwestern plateau, was concentrated along the plateau margin, and migrated from northwest to southeast. Following a period of relative stability of the landscape from ca. 50–30 Ma, significant unroofing of the southwestern plateau interior occurred between ca. 28 and 16 Ma. Additional denudation north of the Grand Canyon took place in latest Tertiary time. Mid-Tertiary dates from the Grand Canyon basement at the bottom of the Upper Granite Gorge limit significant incision of the modern Grand Canyon below the Kaibab surface to <23 Ma. Modeling the age distributions of samples from the basement and Kaibab surface nearby suggests that the gorge and the plateau surface had similar Early to mid-Tertiary thermal histories, despite their >1500 m difference in vertical structural position. If these models are correct, they indicate that a “proto–Grand Canyon” of kilometer-scale depth had incised post-Paleozoic strata by the Early Eocene. Evidence for kilometer-scale mid-Tertiary relief in northeast-fl owing drainages along the plateau margin, as well as the mid-Tertiary episode of plateau interior unroofing, imply that the southwestern plateau interior had attained substantial elevation by at least 25–20 Ma, if not much earlier. These observations are inconsistent with any model calling for exclusively Late Tertiary uplift of the southwestern plateau. Sevier-Laramide plateau surface uplift and incision thus result from one or more processes that enhanced the buoyancy of the plateau lithosphere, expanding the Cordillera’s orogenic highlands into its low-standing cratonic foreland. The onset of the Laramide slab’s demise at ca. 40 Ma and the major pulse of extension in the Basin and Range from ca. 16–10 Ma appear to have had little influence on the denudation history of the southwestern plateau. In contrast, the post-Laramide unroofing episodes may be explained by drainage adjustments induced by rift-related lowering of regions adjacent to the plateau, without the need to otherwise modify the plateau lithosphere. Our data do not preclude a large component of post–Early Eocene elevation gain (or the geodynamic mechanisms it may imply), but they do point toward Laramide-age buoyancy sources as the initial cause of significant surface uplift, ending more than 500 m.y. of residence near sea level.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47378, title ="Stateline fault system: A new component of the Miocene-Quaternary Eastern California shear zone", author = "Guest, Bernard and Niemi, Nathan", journal = "Geological Society of America Bulletin", volume = "119", number = "11-12", pages = "1337-1346", month = "November", year = "2007", doi = "10.1130/0016-7606(2007)119[1337:SFSANC]2.0.CO;2", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-161429519", note = "© 2007 Geological Society of America.\n\nManuscript received 6 November 2006; Revised manuscript received 25 April 2007; Manuscript accepted 24 May 2007.\n\nThis research was supported by Department of\nEnergy contract FC-08-98NV12081 and National\nScience Foundation grant EAR-0453975 to BW and a\nTexaco Postdoctoral Fellowship at the California Institute\nof Technology awarded to BG. Some observations\nin the Devil Peak area were funded by the Lyons Fund\nat the Massachusetts Institute of Technology through\na postdoctoral fellowship to NN. We are especially\ngrateful to D. Burton Slemmons for introducing us\nin the field to a number of Late Quaternary features\nalong the SFS that he and his students have identified and mapped over the years; these features were\nindispensable to our research. Mike Oskin provided\na preprint and critique that substantially improved the\npresentation of fault offsets in the Mojave Desert. Jeff\nLee, Terry Pavlis, and Associate Editor John Wakabayashi\nare thanked for their insightful reviews of the\noriginal manuscript.", revision_no = "13", abstract = "The Eastern California shear zone is an active, north-northwest–trending zone of intraplate right-lateral shear that absorbs ∼25% of Pacific-North America relative plate motion. The Stateline fault system (SFS), which includes several previously recognized, discontinuously exposed Quaternary structures along the California-Nevada border, is in this paper defined as a continuous, 200-km–long zone of active dextral shear that includes (from south to north) the Mesquite, Pahrump, and Amargosa Valley segments. Recognition of this system expands the known extent of the Eastern California shear zone ∼50 km to the east-northeast from its traditionally recognized boundary along the Death Valley fault system. Proximal volcanic and rock avalanche deposits offset across the Mesquite segment of the SFS indicate 30 ± 4 km of slip on this structure since 13.1 ± 0.2 Ma. This offset is an order of magnitude larger than previous estimates across this section of the SFS, but it is consistent with larger offsets previously proposed for the central and northern sections. The total offset and averaged slip rate since mid-Miocene time (2.3 ± 0.35 mm/yr) are similar to those of other major faults across this portion of the Basin and Range, which, from east to west, include the Death Valley, Panamint Valley-Hunter Mountain, and Owens Valley fault systems. However, in contrast to these faults, the average post–mid-Miocene slip rate on the SFS is approximately twice that estimated from present-day geodetic observations and an order of magnitude greater than estimates of average post–mid-Pleistocene slip rates. This discrepancy between long-term, short-term, and geodetically derived slip rates differs from other geologic-geodetic, slip-rate discrepancies in the Eastern California shear zone, where geodetic slip rates are significantly faster than both long-term and short-term geologic slip rates. This suggests that either the slip rate on the SFS has diminished over time, such that the system is an abandoned strand of the relatively young Eastern California shear zone, or that the present-day slip rate represents a transient period of slow slip, such that strands of the shear zone must accommodate a complex spatial and temporal distribution of slip.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47352, title ="(U-Th)/He apatite constraints on the erosional history of the southwestern Colorado Plateau and implications for Early Tertiary uplift and carving of a \"Proto-Grand Canyon\"", author = "Flowers, R. M. and Wernicke, B. P.", journal = "Geochimica et Cosmochimica Acta", volume = "71", number = "15", pages = "A287", month = "August", year = "2007", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-155445054", note = "© 2007 Published by Elsevier Ltd.", revision_no = "11", abstract = "Resolving the timing and relationships between regional\nunroofing, canyon incision, and topographic uplift in\ncontinental plateaus is a challenging problem. The regional\nunroofing history of the Colorado Plateau, and its relationship\nto Grand Canyon incision (up to 1.5 km) and plateau uplift\n(~1.9 km) since the Late Cretaceous, is controversial. We\nused (U-Th)/He apatite thermochronometry (36 samples, 230\nsingle-grain analyses) across the southwestern quadrant of the\nColorado Plateau to address these issues. Our data document\noverall southwest to northeast unroofing from plateau margin\nto plateau interior, during denudation phases in the Late\nCretaceous/Early Tertiary (80 to 55 Ma), mid Tertiary (28 to\n16 Ma), and Late Tertiary (<6 Ma). Distributions of apatite\ndates modeled using the radiation damage trapping model\n[1,2] suggest that eastern Grand Canyon samples from the\nbasement and the Kaibab surface nearby had similar Early to\nmid-Tertiary thermal histories, despite their ~1500 m of\nstratigraphic separation. If these models are correct, they\nindicate that a significant (≥ 1000 m deep) paleo-Grand\nCanyon was carved in post-Paleozoic sediments in this region\nduring Early Tertiary time. Evidence for kilometer-scale\ntopographic relief would require substantial uplift during\nSevier/Laramide time, preceding regional unroofing of this\nportion of the plateau interior. Although the data do not\npreclude additional post-Laramide uplift, the subsequent\nregional unroofing phases could be explained by drainage\nreorganization associated with rift-related lowering of adjacent\nregions without additional elevation gain of the plateau.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/39514, title ="Paleoaltimetry from \"clumped\" ^(13)C-^(18)O bonds in carbonates, Colorado Plateau", author = "Huntington, Katharine and Wernicke, Brian", journal = "Geochimica et Cosmochimica Acta", volume = "71", number = "15", pages = "A426", month = "August", year = "2007", doi = "10.1016/j.gca.2007.06.017", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130723-084848939", note = "© 2007 Published by Elsevier Ltd.", revision_no = "14", abstract = "The elevation history of Earth’s surface is a key element\nlinking tectonic, geodynamic, climatic, and surface processes,\nbut remains difficult to reconstruct from the geologic record.\nIn contrast to conventional stable isotope paleoaltimetry\napproaches, the new “clumped” ^(13)C-^(18)O paleothermometer\nindependently determines carbonate growth temperature and\nthe δ^(18)O of water from which the carbonate grew, potentially\nenabling the effects of altitude, climate, and seasonality to be\ndistinguished. This approach has been successfully applied to\npaleosol nodules. Here, we examine what other materials may\npotentially access paleoelevation information using this\ntechnique, including gastropods, the bivalve anomia, oysters,\nbarnacles, soil, marl, and limestone from Cretaceous to\nPliocene deposits from and adjacent to the Colorado Plateau,\nsouthwestern USA.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20806, title ="Geology and thermochronology of Tertiary Cordilleran-style metamorphic core complexes in the Saghand region of central Iran", author = "Verdel, Charles and Wernicke, Brian P.", journal = "Geological Society of America Bulletin", volume = "119", number = "7-8", pages = "961-977", month = "July", year = "2007", doi = "10.1130/B26102.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101115-103409069", note = "© 2007 Geological Society of America.\nManuscript received 12 September 2006; Revised manuscript received 1 February 2007; Manuscript accepted 14 February 2007.\nWe thank the University of Tehran Research\nCouncil for their support of this project and\nAhmad Reza Malekpour for his efforts in the\nfield. Ken Farley, Rebecca Flowers, and Lindsey\nHedges provided assistance with the (U-Th)/He\nanalyses. Bernard Guest and Kevin Mahan conducted\ninformal reviews of an early version\nof the manuscript. Mahan also offered helpful\nadvice in microstructural analysis. Comments from Mark Allen, David Foster, and Uwe Ring\nimproved the manuscript. Financial support for\nthis project was provided by the Caltech Tectonics\nObservatory and National Science Foundation\ngrant EAR-0511054.", revision_no = "15", abstract = "An ~100-km-long north-south belt of metamorphic core complexes is localized along the boundary between the Yazd and Tabas tectonic blocks of the central Iranian micro-continent, between the towns of Saghand and Posht-e-Badam. Amphibolite facies mylonitic gneisses are structurally overlain by east-tilted supracrustal rocks including thick (>1 km), steeply dipping, nonmarine siliciclastic and volcanic strata. Near the detachment (the Neybaz-Chatak fault), the gneisses are generally overprinted by chlorite brecciation. Crosscutting relationships along with U-Pb zircon and ^(40)Ar/^(39)Ar age data indicate that migmatization, mylonitic deformation, volcanism, and sedimentation all occurred in the middle Eocene, between ca. 49 and 41 Ma. The westernmost portion of the Tabas block immediately east of the complexes is an east-tilted crustal section of Neoproterozoic–Cambrian crystalline rocks and metasedi-mentary strata >10 km thick. The ^(40)Ar/^(39)Ar biotite ages of 150–160 Ma from structurally deep parts of the section contrast with ages of 218–295 Ma from shallower parts, and suggest Late Jurassic tilting of the crustal section. These results define three events: (1) a Late Jurassic period of upper crustal cooling of the western Tabas block that corresponds to regional Jurassic–Cretaceous tectonism and erosion recorded by a strong angular unconformity below mid-Cretaceous strata throughout central Iran; (2) profound, approximately east-west middle Eocene crustal extension, plutonism, and volcanism (ca. 44–40 Ma); and (3) ~2–3 km of early Miocene (ca. 20 Ma) erosional exhumation of both core complex and Tabas block assemblages at uppermost crustal levels, resulting from significant north-south shortening. The discovery of these and other complexes within the mid-Tertiary magmatic arcs of Iran demonstrates that Cordilleran-style core complexes are an important tectonic element in all major segments of the Alpine-Himalayan orogenic system.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47363, title ="Cosmogenic ^(10)Be and ^(36)Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone", author = "Frankel, Kurt L. and Brantley, Katherine S.", journal = "Journal of Geophysical Research B", volume = "112", number = "B6", pages = "Art. No. B06407", month = "June", year = "2007", doi = "10.1029/2006JB004350", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-100630734", note = "© 2007 The American Geophysical Union. \n\nReceived 15 February 2006; Revised 16 January 2007; Accepted 30 January 2007; Published 13 June 2007. \n\nWe thank Patrick Belmont, David Bowman, Stephanie Briggs, Charles Sammis, and Jeremy Zechar for thought provoking discussions. Patrick Belmont is also thanked for his assistance\nwith field work. Permission to collect samples and access field sites within Death Valley National Park was granted by the Death Valley National Park Service Natural Resources Office. ALSM data were acquired by the National Center for Airborne Laser Swath Mapping (NCALM) at the University of Florida. This research was funded by NSF grant EAR-0207365, NCALM, the Southern California Earthquake Center (SCEC), the University of California, Lawrence Livermore National Laboratory UEPP program, a NASA Earth System Science Fellowship, the Geological Society of America, Sigma Xi, and the USC Department of Earth Sciences. SCEC is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008. This is SCEC contribution 958. This study was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory, contract B539647. Gilles Peltzer, Lucilla Benedetti, and Isabelle Manighetti provided reviews that helped improve the manuscript.", revision_no = "26", abstract = "The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right-lateral strike-slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high-resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ∼297 ± 9 m of right-lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic ^(10)Be and ^(36)Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/−20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on ^(36)Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic ^(10)Be date yields a geologic fault slip rate of 4.2 +1.9/−1.1 mm yr^(−1), whereas the ^(36)Cl data indicate 4.7 +0.9/−0.6 mm yr^(−1) of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ∼8.5 to 10 mm yr^(−1). This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20810, title ="Radiation damage control on apatite (U-Th)/He dates from the Grand Canyon region, Colorado Plateau", author = "Flowers, R. M. and Shuster, D. L.", journal = "Geology", volume = "35", number = "5", pages = "447-450", month = "May", year = "2007", doi = "10.1130/G23471A.1 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101115-112300013", note = "© 2007 Geological Society of America. \n\nManuscript received 22 October 2006. Revised manuscript received 21 December 2006. Manuscript accepted 29 December 2006. \n\nThis work was supported by The Caltech Tectonics Observatory and National Science Foundation grants EAR-0610115 and EAR-0408526. Constructive reviews by Trevor Dumitru, Shari Kelley, Jon Spencer, and Daniel Stockli helped to clarify the manuscript.", revision_no = "16", abstract = "Individual detrital apatite grains from the Esplanade, Coconino, and Moenkopi Formations in the Grand Canyon region of the Colorado Plateau yield (U-Th)/He dates from 104 to 5 Ma. The range of dates within each unit far exceeds analytical uncertainty, but correlates with both He concentration [He] and effective U concentration [eU]. These dates are all significantly younger than the sandstone units, indicating partial to complete He loss following deposition. Recently published laboratory diffusion data suggest that He retentivity in apatite increases with radiation damage. Forward models predict that the consequences of this effect will be manifested most clearly as a correlation between (U-Th)/He dates and the [He] and [eU] in suites of apatites that (1) are characterized by a large span of [eU], and (2) had thermal histories in which sufficient time elapsed for the apatite He diffusion kinetics to diverge prior to reheating and partial resetting. Apatites in the sedimentary units investigated fit these cri teria. Using geologically reasonable deposition, burial, and unroofing histories, simulations that include the effect of radiation damage on apatite He retentivity can reproduce the observed distributions of apatite dates and correlations with parent and daughter concentrations. These results suggest that a span of (U-Th)/He dates positively correlated with [eU] may provide important information regarding a sample's thermal history.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47354, title ="Evidence for radiation damage control on apatite He ages from the Grand Canyon region, Colorado Plateau", author = "Flowers, R. M. and Shuster, D. L.", journal = "Geochimica et Cosmochimica Acta", volume = "70", number = "18", pages = "A178", month = "August", year = "2006", doi = "10.1016/j.gca.2006.06.358", issn = "0016-7037", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-082435010", note = "© 2006 Published by Elsevier Ltd.", revision_no = "11", abstract = "Individual detrital apatites from three sedimentary units in\nthe Grand Canyon region of the Colorado Plateau yield a span\nof (U-Th)/He dates that are positively correlated with\nradiogenic ^4He and effective U (eU) concentrations. All dates\nare younger than the depositional ages of the sandstone units,\nindicating partial to complete ^4He loss in the analyzed apatites\nfollowing deposition. Recent refinements in our\nunderstanding of He diffusion based on laboratory\nexperiments suggest that radiation damage impedes He\nmobility in apatite [1]. Forward models that incorporate the\neffect of evolving He diffusivities indicate that this behavior\nwill be most strongly manifested by suites of apatites\ncontaining a range of eU concentrations that cooled and were\npartially reset. Detrital apatite grains from sedimentary units\nin the Grand Canyon region fit these criteria when 1)\ncompositionally variable apatites were deposited, and 2)\nunderwent burial heating, partial ^4He loss, and subsequent\nexhumation. Using geologically reasonable thermal histories,\nour simulations can reproduce our distributions of detrital\napatite dates. The youngest dates are obtained for the lowest\neU apatites that underwent the greatest ^4He loss during burial,\nand impose the strongest constraint on the exhumation\ntiming. The results also predict that the correlations between\nage and ^4He and eU concentrations are sensitive to the\nthermal history, such that it may be possible to extract\nadditional details regarding temperature-time paths from\nthese relationships.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20843, title ="Subcontinental-scale crustal velocity changes along the Pacific–North America plate boundary", author = "Davis, J. L. and Wernicke, B. P.", journal = "Nature", volume = "441", number = "7097", pages = "1131-1134", month = "June", year = "2006", doi = "10.1038/nature04781 ", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101117-083117982", note = "© 2006 Nature Publishing Group.\n\nReceived 1 December 2005; accepted 3 April 2006.\nThis work was supported by the National Science\nFoundation and the US Department of Energy. UNAVCO, Inc., supports\nBARGEN site implementation, operation and maintenance. The authors thank\nR. Bürgmann for comments on the manuscript.", revision_no = "14", abstract = "Transient tectonic deformation has long been noted within approx100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (~1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse ~1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific–North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by ~1 mm yr^(-1) starting in late 1999.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20746, title ="An animated tectonic reconstruction of southwestern North America since 36 Ma", author = "McQuarrie, Nadine and Wernicke, Brian P.", journal = "Geosphere", volume = "1", number = "3", pages = "147-172", month = "December", year = "2005", doi = "10.1130/GES00016.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101110-111024631", note = "© 2005 Geological Society of America.\nManuscript received by the Society 5 April 2005; revised manuscript received 29 August 2005; manuscript accepted 23 September 2005.\nThis paper has benefited greatly from many conversations\nwith scientists familiar with western\nNorth America geology. We specifically want to acknowledge\nTanya Atwater, Bill Dickinson, Allen\nGlazner, Steve Graham, Jon Spencer, Joann Stock,\nNathan Niemi, Mike Oskin, Jason Saleeby, and\nJohn Suppe. We are grateful to Melissa Brenneman\nat the University of Redlands for creating the\nArcMap document and script used for the reconstruction.\nThe movie would not exist without the\nhelp of the University of California, Santa Barbara,\nEducational Multimedia Visualization Center, specifically\nCarrie Glavich and Grace Giles. Gary\nAxen, Doug Walker, Craig Jones, and Randy Keller\nall provided insightful feedback through the review\nprocesses that greatly improved the clarity of presentation.\nThis project was funded by the Caltech\nTectonics Observatory.", revision_no = "17", abstract = "We present tectonic reconstructions and\nan accompanying animation of deformation\nacross the North America–Pacific plate\nboundary since 36 Ma. Intraplate deformation\nof southwestern North America was\nobtained through synthesis of kinematic\ndata (amount, timing, and direction of displacement)\nalong three main transects\nthrough the northern (40°N), central (36°N–\n37°N), and southern (34°N) portions of the\nBasin and Range province. We combined\nthese transects with first-order plate boundary\nconstraints from the San Andreas fault\nand other areas west of the Basin and\nRange. Extension and strike-slip deformation\nin all areas were sequentially restored\nover 2 m.y. (0–18 Ma) to 6 m.y. (18–36 Ma)\ntime intervals using a script written for the\nArcGIS program. Regions where the kinematics\nare known constrain adjacent areas\nwhere the kinematics are not well defined.\nThe process of sequential restoration highlighted\nmisalignments, overlaps, or large\ngaps in each incremental step, particularly\nin the areas between data transects, which\nremain problematic. Hence, the value of the\nreconstructions lies primarily in highlighting\nquestions that might not otherwise be\nrecognized, and thus they should be viewed\nmore as a tool for investigation than as a\nfinal product.\nThe new sequential reconstructions show\nthat compatible slip along the entire northsouth\nextent of the inland right-lateral\nshear zone from the Gulf of California to\nthe northern Walker Lane is supported by\navailable data and that the east limit of active\nshear has migrated westward with respect\nto North America since ca. 10 Ma.\nThe reconstructions also highlight new\nproblems regarding strain-compatible extension\neast and west of the Sierra Nevada–\nGreat Valley block and strain-compatible\ndeformation between southern Arizona and\nthe Mexican Basin and Range. Our results\nshow ~235 km of extension oriented\n~N78°W in both the northern (50% extension)\nand central (200% extension) parts of\nthe Basin and Range. Following the initiation\nof east-west to southwest-northeast extension\nat 15–25 Ma (depending on longitude),\na significant portion of right-lateral\nshear associated with the growing Pacific–\nNorth America transform jumped into the\ncontinent at 10–12 Ma, totaling ~100 km\noriented N25°W, for an average of ~1 cm/yr since that time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20887, title ="Tectonic implications of a dense continuous GPS velocity field at Yucca Mountain, Nevada", author = "Wernicke, Brian and Davis, James L.", journal = "Journal of Geophysical Research B", volume = "109", number = "B12", pages = "Art. No. B12404", month = "December", year = "2004", doi = "10.1029/2003JB002832 ", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101118-104543598", note = "© 2004 American Geophysical Union.\n\nReceived 7 October 2003; revised 3 July 2004; accepted 8 September 2004; published 15 December 2004.\nThis research was supported by DOE contract\nFC-08-98NV12081. Operation and analysis of the northern part of the\nBARGEN network was supported by NSF grants EAR-0135457 and EAR-0136102. Geodetic sites were constructed with technical assistance from the\nUniversity NAVSTAR Consortium (UNAVCO) facility. Several of the figures\nwere prepared using Generic Mapping Tools (GMT) version 3.4.2 [Wessel\nand Smith, 1998]. We are grateful to T. Herring for sharing calculations on\npostseismic effects of the Hector Mine earthquake in the Yucca Mountain\narea, and J. Price and G. Blewitt for discussions. We thank reviewers T. H.\nDixon and J. C. Savage, and Associate Editor Y. Bock for constructive\nsuggestions that substantially improved the quality of the manuscript.", revision_no = "17", abstract = "A dense, continuous GPS network was established in the Yucca Mountain area in 1999 to provide the most reliable measurements possible of geodetic strain patterns across the nation's only proposed permanent repository for high-level radioactive waste. The network lies astride a boundary between the geodetically stable central Great Basin and the active western Great Basin, which at the latitude of Yucca Mountain is undergoing distributed right-lateral shear at a rate of ~60 nstrain/yr. Monitoring from 1999 to 2003 (3.75 years) yields a velocity field characterized by nearly homogenous N20°W right-lateral shear of 20 ± 2 nstrain/yr (net velocity contrast of ~1.2 mm/yr across a 60 km aperture) in the vicinity of the proposed repository site. Comparison of time series of continuous results with earlier campaign surveys indicating ~50 nstrain/yr of west-northwest extension from 1991 to 1997 suggests that the more rapid rates were in part transient motions associated with the 1992 M s 5.4 Little Skull Mountain earthquake. Postseismic motions do not appear to affect the 1999–2003 velocity field in either campaign or continuous data. The magnitude of the velocity contrast across the area, the overall linearity of the gradient, and the large area of undeforming crust to the east of Yucca Mountain are difficult to explain by elastic bending of the crust associated with the Death Valley fault zone, a major right-lateral strike-slip fault about 50 km west of the repository site. These observations, along with apparent local variations in the velocity gradient, suggest that significant right-lateral strain accumulation, with displacement rate in the 1 mm/yr range, may be associated with structures in the Yucca Mountain area. The absence of structures in the area with equivalent late Quaternary displacement rates underscores the problem of reconciling discrepancies between geologic and geodetic estimates of deformation rates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20969, title ="BARGEN continuous GPS data across the eastern Basin and Range province, and implications for fault system dynamics", author = "Niemi, Nathan A. and Wernicke, Brian P.", journal = "Geophysical Journal International", volume = "159", number = "3", pages = "842-862", month = "December", year = "2004", doi = "10.1111/j.1365-246X.2004.02454.x ", issn = "0956-540X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101123-090925415", note = "© 2004 RAS. \n\nAccepted 2004 July 26. Received 2003 March 25; in original form 2001 February 23. Article first published online: 20 Oct. 2004. \n\nBARGEN research is funded by the National Science Foundation (grants EAR 97-25766, 99-03366 and 00-01209), the Yucca Mountain Project of the US Department of Energy, and the Solid Earth and Hazards Program of NASA. Support for this work was also provided by an NSF Graduate Fellowship (NAN). Network design and maintenance assistance is provided by the University NAVSTAR Consortium (UNAVCO) Facility in Boulder, Colorado, the University of Nevada, Reno, and the University of Utah. We thank Tim Dixon and John Oldow for productive comments on this manuscript.", revision_no = "19", abstract = "We collected data from a transect of continuous Global Positioning System (GPS) sites across the eastern Basin and Range province at latitude 39°N from 1997–2000. Intersite velocities define a region ~350 km wide of broadly distributed strain accumulation at ~10 nstr yr^(−1). On the western margin of the region, site EGAN, ~10 km north of Ely, Nevada, moved at a rate of 3.9 ± 0.2 mm yr^(−1) to the west relative to site CAST, which is on the Colorado Plateau. Velocities of most sites to the west of Ely moved at an average rate of ~3 mm yr^(−1) relative to CAST, defining an area across central Nevada that does not appear to be extending significantly. The late Quaternary geological velocity field, derived using seismic reflection and neotectonic data, indicates a maximum velocity of EGAN with respect to the Colorado Plateau of ~4 mm yr^(−1), also distributed relatively evenly across the region. The geodetic and late Quaternary geological velocity fields, therefore, are consistent, but strain release on the Sevier Desert detachment and the Wasatch fault appears to have been anomalously high in the Holocene. Previous models suggesting horizontal displacement rates in the eastern Basin and Range near 3 mm yr^(−1), which focused mainly along the Wasatch zone and Intermountain seismic belt, may overestimate the Holocene Wasatch rate by at least 50 per cent and the Quaternary rate by nearly an order of magnitude, while ignoring potentially major seismogenic faults further to the west.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20966, title ="Evidence for Deep Magma Injection Beneath Lake Tahoe, Nevada-California", author = "Smith, Kenneth D. and von Seggern, David", journal = "Science", volume = "305", number = "5688", pages = "1277-1280", month = "August", year = "2004", doi = "10.1126/science.1101304 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101123-081625102", note = "© 2004 American Association for the Advancement of Science. \n\nReceived 9 June 2004; accepted 28 July 2004. Published online 5 August 2004. \n\nThe University of Nevada, Reno seismic network in\nnorthern Nevada is operated under the U.S. Geological\nSurvey National Earthquake Hazards Reduction\nProgram with support from the State of Nevada. The\nGPS data analysis was funded by the Department of\nEnergy, Yucca Mountain Project. The BARGEN GPS\nnetwork is funded by NSF and the Department of\nEnergy, with operational support from UNAVCO, Inc.\nThe GIPSY OASIS II software and global GPS data\nproducts were provided by the Jet Propulsion Laboratory.\nWe thank G. Oppliger for a review of the\nmanuscript and M. Coolbaugh for generating the\nregional strain map figure. Several stations in the\nNevada K-12 seismic network, Storey County High\nSchool, Carson City High School, and Douglas County\nHigh School contributed phase arrival data for constraining\nearthquake locations in the lower-crustal\nswarm. We thank three anonymous reviewers for\ntheir time and effort in reviewing the manuscript.", revision_no = "24", abstract = "A deep earthquake swarm in late 2003 at Lake Tahoe, California (Richter magnitude < 2.2; depth of 29 to 33 kilometers), was coeval with a transient displacement of 6 millimeters horizontally outward from the swarm and 8 millimeters upward measured at global positioning system station Slide Mountain (SLID) 18 kilometers to the northeast. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters per second up-dip along a 40-square-kilometer structure striking north 30° west and dipping 50° to the northeast. SLID's transient velocity of 20 millimeters per year implies a lower bound of 200 nanostrains per year (parts per billion per year) on local strain rates, an order of magnitude greater than the 1996 to 2003 regional rate. The geodetic displacement is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20970, title ="Geologic context of geodetic data across a Basin and Range normal fault, Crescent Valley, Nevada", author = "Friedrich, A. M. and Lee, J.", journal = "Tectonics", volume = "23", number = "2", pages = "Art. No. TC2015", month = "April", year = "2004", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101123-092252306", note = "© 2004 American Geophysical Union. \n\nReceived 31 March 2003; revised 16 October 2003; accepted 18 November 2003; published 16 April 2004. \n\nThis study was supported by NSF grants\nEAR 99-03366 and EAR-00-01209 awarded to B. Wernicke and K. Sieh,\nand grant EAR-9902968 awarded to J. Lee. A. Friedrich acknowledges\nadditional financial support from the University of Potsdam. We thank\nM. Jackson and R. Bruhn for providing surveying equipment, and\nB. Phillibosian, R. Heermance, and J. Liu for valuable assistance in the\nfield. We benefited from reviews by D. Hindle, S. Mc Gill, and R. Hetzel\nand discussions with J. Bell, J. Caskey, C. DePolo, K. Haller, M. Machette,\nA. Ramelli, and S. Wesnousky on Basin and Range paleoseismology.\n\nAuxiliary material for this article contains excavation logs, fault scarp measurements along the Cortez range front, and stratigraphic descriptions of unit exposed in the excavation on the north side of Fourmile Canyon.", revision_no = "25", abstract = "Geodetic strain and late Quaternary faulting in the Basin and Range province is distributed over a region much wider than historic seismicity, which is localized near the margins of the province. In the relatively aseismic interior, both the magnitude and direction of geodetic strain may be inconsistent with the Holocene faulting record. We document the best example of such a disagreement across the NE striking, ~55° NW dipping Crescent normal fault, where a NW oriented, 70 km geodetic baseline records contemporary shortening of ~2 mm/yr orthogonal to the fault trace. In contrast, our geomorphic, paleoseismic, and geochronologic analyses of the Crescent fault suggest that a large extensional rupture occurred during the late Holocene epoch. An excavation across the fault at Fourmile Canyon reveals that the most recent event occurred at 2.8 ± 0.1 ka, with net vertical tectonic displacement of 4.6 ± 0.4 m at this location, corresponding to the release of ~3 m of accumulated NW-SE extension. Measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event, implying a moment magnitude M_w of at least 6.6. No prior event occurred between ~2.8 ka and ~6.4 ± 0.1 ka, the ^(14)C calender age of strata near the base of the exposed section. Assuming typical slip rates for Basin and Range faults (~0.3 mm/yr), these results imply that up to one third, or ~1 m, of the extensional strain released in the previous earthquake could have reaccumulated across the fault since ~2.8 ka. However, the contemporary shortening implies that the fault is unloading due to a transient process, whose duration is limited to between 6 years (geodetic recording time) and 2.8 ka (the age of the most recent event). These results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20980, title ="Cenozoic evolution of Neotethys and implications for the causes of plate motions", author = "McQuarrie, N. and Stock, J. M.", journal = "Geophysical Research Letters", volume = "30", number = "20", pages = "Art. No. 2036", month = "October", year = "2003", doi = "10.1029/2003GL017992 ", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101123-103005860", note = "© 2003 American Geophysical Union.\n\nReceived 17 June 2003; revised 26 August 2003; accepted 2 September 2003; published 21 October 2003.\n\nWe thank Peter Molnar and Dietmar Mueller\nfor their reviews. This work was supported by the Caltech Tectonic\nObservatory.", revision_no = "20", abstract = "Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations and new estimates of crustal shortening in Iran define the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia. The new constraints indicate that Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with slowing of Africa-Eurasia motion to <1 cm/yr near 25 Ma, coeval with the opening of the Red Sea. Ocean closure occurred no later than 10 Ma, and could have occurred prior to this time only if a large amount of continental lithosphere was subducted, suggesting that slowing of Africa significantly predated the Arabia-Eurasia collision. These kinematics imply that Africa's disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern Eurasia slowed its motion. The slow, steady rate of northward subduction since 56 Ma contrasts with strongly variable rates of magma production in the Urumieh-Dokhtar arc, implying magma production rate in continental arcs is not linked to subduction rate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47351, title ="Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range", author = "Park, Stephen K. and Wernicke, Brian", journal = "Tectonics", volume = "22", number = "4", pages = "Art. No. 1030", month = "August", year = "2003", doi = "10.1029/2001TC001324", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-152004214", note = "© 2003 The American Geophysical Union.\n\nReceived 4 September 2001; Revised 4 August 2002; Accepted 27 August 2002; Published 9 July 2003.\n\nSupport from the National Science Foundation’s\nContinental Dynamics Programs under grants EAR9526992 (S. K.\nPark) and EAR9526895 (B. Wernicke) is gratefully appreciated. Broadband\ndata acquisition was supervised by George Jiracek for MT stations 101–\n130. Robert Bielinski, Scott Elrick, and Richard Funk helped in the data\nacquisition for the long period stations in 1997. We also thank Death Valley\nNational Park and Sequoia-Kings Canyon National Park scientists for their\nassistance in this study. Reviews by Phillip Wannamaker, John Booker, and\nAssociate Editor Darrel Cowan helped improve this manuscript greatly.", revision_no = "12", abstract = "Comparison of an electrical resistivity section derived from magnetotelluric (MT) data to a geologic section extending eastward from the Sierra Nevada near latitude 36°20′N shows that the crust is dominated by steeply dipping conductive features that correlate with active strike-slip faults. While there is a subhorizontal conductor at a depth ∼20 km beneath some of the profile, it is broken by vertical structures associated with the active strike-slip faults. The continuous subhorizontal anomalies in the lower crust typically observed in extensional regions are therefore absent in the resistivity section. The present-day strike-slip tectonic regime as indicated by geodetic data in this part of the Basin and Range is not producing features that could be inferred to indicate subhorizontal shear zones resulting from lateral crustal flow during extension. Because the Miocene tectonic regime resulted in the formation of metamorphic core complexes and thus was accompanied by such flow, the present regime appears to represent a fundamental transition in the mode of crustal deformation in the region. A serendipitous result of our study was the identification on resistivity sections of carbonate aquifers in the upper crust. Comparison of resistivities from the MT section to measured fluid resistivities from springs and boreholes suggests that the aquifers must be heterogeneous, with more saline brines occupying the deepest portions of the carbonates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47366, title ="Comparison of geodetic and geologic data from the Wasatch region, Utah, and implications for the spectral character of Earth deformation at periods of 10 to 10 million years", author = "Friedrich, Anke M. and Wernicke, Brian P.", journal = "Journal of Geophysical Research B", volume = "108", number = "B4", pages = "Art. No. 2199", month = "April", year = "2003", doi = "10.1029/2001JB000682", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-123455534", note = "© 2003 The American Geophysical Union.\n\nReceived 22 June 2001; Revised 2 June 2002; Accepted 21 November 2002; Published 15 April 2003.\n\nThis research was supported by National\nScience Foundation grants EAR-97-25766 and 99-03366 awarded to B.\nWernicke and NASA grant NAG5-8226 and USGS 99HQGR0212 awarded\nto R. Bennett. We thank F. Albarede, W. Thatcher, S. Wesnousky and an\nanonymous reviewer for constructive comments that greatly improved the\npresentation. We thank J. Bartley, D. Currey, K. Haller, M. Machette, K. Hanson, E. Lips, A. Mattson, S. Olig, J. Pechman, M. Simons, and R. B.\nSmith for useful discussions on the geophysics and Quaternary history of\nthe Wasatch region. Special thanks to D. Dinter and J. Pechmann for\npermission to discuss unpublished data on the seismic history of the East\nGreat Salt Lake fault and to E. Lips for permission to discuss unpublished\ndata on the late Quaternary history of the Little Cottonwood area.", revision_no = "13", abstract = "The Wasatch fault and adjacent fault zones provide an opportunity to compare present-day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows, ranging from the last millennium up to 10 Myr. The three easternmost GPS sites of the Basin and Range Geodetic Network (BARGEN) at this latitude define a ∼130-km-wide region spanning three major normal faults extending east-west at a total rate of 2.7 ± 0.4 mm/yr, with an average regional strain rate estimated to be 21 ± 4 nstrain/yr, about twice the Basin and Range average. On the Wasatch fault, the vertical component of the geologic displacement rate is 1.7 ± 0.5 mm/yr since 6 ka, <0.6 mm/yr since 130 ka, and 0.5–0.7 mm/yr since 10 Ma. However, it appears likely that at the longest timescale, rates slowed over time, from 1.0 to 1.4 mm/yr between 10 and 6 Ma to 0.2 to 0.3 mm/yr since 6 Ma. The cumulative vertical displacement record across all three faults also shows time-variable strain release ranging from 2 to 4 mm/yr since 10 ka to <1 mm/yr averaged over the past 130 kyr. Conventional earthquake recurrence models (“Reid-type” behavior) would require an accordingly large variation in strain accumulation or loading rate on a 10-kyr timescale, for which there appears to be no obvious geophysical explanation. Alternatively, seismic strain release, given a wide range of plausible constitutive behaviors for frictional sliding, may be clustered on the 10-kyr timescale, resulting in the high Holocene rates, with comparatively low, uniform strain accumulation rates on the 100-kyr timescale (“Wallace-type” behavior). The latter alternative, combined with observations at the million-year timescale and the likelihood of a significant contribution of postseismic transients, implies maxima of spectral amplitude in the velocity field at periods of ∼10 Myr (variations in tectonic loading), ∼10 kyr (clustered strain release), and of 100 years (postseismic transients). If so, measurements of strain accumulation and strain release may be strongly timescale-dependent for any given fault system.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47377, title ="Assessment of GPS velocity accuracy for the Basin and Range Geodetic Network (BARGEN)", author = "Davis, J. L. and Bennett, R. A.", journal = "Geophysical Research Letters", volume = "30", number = "7", pages = "Art. No. 1411", month = "April", year = "2003", doi = "10.1029/2003GL016961 ", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-154842013", note = "© 2003 by the American Geophysical Union.\n\nReceived 21 January 2003; revised 11 March 2003; accepted 13 March 2003; published 11 April 2003.\n\nThis research was supported by the National\nScience Foundation, the Department of Energy, NASA, the UNAVCO\nFacility, the California Institute of Technology, the Smithsonian Institution,\nand the University of Nevada, Reno. We thank P. Elósegui, H. Johnson,\nand an anonymous reviewer for useful comments on the manuscript. We\nalso thank J. Langbein and R. King for comments on an earlier version of\nthis work.", revision_no = "10", abstract = "We assess the accuracy of horizontal velocity estimates from the Basin and Range Geodetic Network (BARGEN), a continuous GPS network that has been in operation since 1996. To make this quantitative assessment, we use a procedure that we term the “whole-error” method. In this method, the measure of the velocity errors is the root-mean-square (RMS) residual velocity relative to a simple geophysical model. This method produces a conservative estimate of the uncertainties, since errors in the geophysical models also contribute to the RMS residual. Using estimates from two different BARGEN subnetworks, the Northern Basin and Range and the Yucca Mountain Cluster, we determine velocity uncertainties of 0.1–0.2 mm yr^(−1). Since BARGEN covers a significant fraction of area of the proposed Plate Boundary Observatory component of EarthScope, our results indicate a good ability of this project to determine highly accurate long-term horizontal crustal velocities and deformation rates in this region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47362, title ="Contemporary strain rates in the northern Basin and Range province from GPS data", author = "Bennett, R. A. and Wernicke, B. P.", journal = "Tectonics", volume = "22", number = "2", pages = "Art. No. 1008", month = "April", year = "2003", doi = "10.1029/2001TC001355", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-091502511", note = "© 2003 The American Geophysical Union.\n\nReceived 5 November 2001; Revised 29 August 2002; Accepted 6 September 2002; Published 21 March 2003.\n\nWe made use of data from the BARD CGPS\nnetwork operated by the University of California, Berkeley. We also made\nuse of GPS data products provided by the SOPAC facility. We thank\nTimothy Dixon, Weijun Gan, and Wayne Thatcher for providing GPS\nvelocity results and James Savage for details about some of the GPS\ncampaign data. Parts of the figures were produced with the GMT software.\nWe benefited from the comments and suggestions of Darrel Cowan, Tim\nDixon, and an anonymous reviewer. This work was supported by DOE\ngrants DE FC08-98NV 12081, NASA grant NAG5-8226, NSF grants EAR\n94-18784 and EAR 97-25766, and USGS grant 99HQGR0212, California\nInstitute of Technology, and the Smithsonian Institution.", revision_no = "12", abstract = "We investigate the distribution of active deformation in the northern Basin and Range province using data from continuous GPS (CGPS) networks, supplemented by additional campaign data from the Death Valley, northern Basin and Range, and Sierra Nevada–Great Valley regions. To understand the contemporary strain rate field in the context of the greater Pacific (P)–North America (NA) plate boundary zone, we use GPS velocities to estimate the average relative motions of the Colorado Plateau (CP), the Sierra Nevada–Great Valley (SNGV) microplate, and a narrow north-south elongate region in the central Great Basin (CGB) occupying the longitude band 114–117°W. We find that the SNGV microplate translates with respect to the CP at a rate of 11.4 ± 0.3 mm yr^(−1) oriented N47 ± 1°W and with respect to NA at a rate of ∼12.4 mm yr^(−1) also oriented N47°W, slower than most previous geodetic estimates of SNGV-NA relative motion, and nearly 7° counterclockwise from the direction of P-NA relative plate motion. We estimate CGB-CP relative motion of 2.8 ± 0.2 mm yr^(−1) oriented N84 ± 5°W, consistent with roughly east-west extension within the eastern Great Basin (EGB). Velocity estimates from the EGB reveal diffuse extension across this region, with more rapid extension of 20 ± 1 nstr yr^(−1) concentrated in the eastern half of the region, which includes the Wasatch fault zone. We estimate SNGV-CGB relative motion of 9.3 ± 0.2 mm yr^(−1) oriented N37 ± 2°W, essentially parallel to P-NA relative plate motion. This rate is significantly slower than most previous geodetic estimates of deformation across the western Great Basin (WGB) but is generally consistent with paleoseismological inferences. The WGB region accommodates N37°W directed right lateral shear at rates of (1) 57 ± 9 nstr yr^(−1) across a zone of width ∼125 km in the south (latitude ∼36°N), (2) 25 ± 5 nstr yr^(−1) in the central region (latitude ∼38°N), and (3) 36 ± 1 nstr yr^(−1) across a zone of width ∼300 km in the north (latitude ∼40°N). By construction there is no net extension or shortening perpendicular to SNGV-CGB relative motion. However, we observe about 8.6 ± 0.5 nstr yr^(−1) extension on average in the direction of shear from southeast to northwest within the Walker Lane belt, comparable to the average east-west extension rate of 10 ± 1 nstr yr^(−1) across the northern Basin and Range but implying a distinctly different mechanism of deformation from extension on north trending, range-bounding normal faults. An alternative model for this shear parallel deformation, in which extension is accommodated across a narrow, more rapidly extending zone that coincides with the central Nevada seismic belt, fits the WGB data slightly better. Local anomalies with respect to this simple kinematic model may reveal second-order deformation signals related to more local crustal dynamic phenomena, but significant improvements in velocity field resolution will be necessary to reveal this second-order pattern.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47395, title ="Crustal loading near Great Salt Lake, Utah", author = "Elósegui, P. and Davis, J. L.", journal = "Geophysical Research Letters", volume = "30", number = "3", pages = "Art. No. 1111", month = "February", year = "2003", doi = "10.1029/2002GL016579", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140722-104759354", note = "© 2003 American Geophysical Union.\n\nReceived 7 November 2002; revised 4 December 2002; accepted 23 December 2002; published 5 February 2003.\n\nWe thank C. Burden of the U.S.G.S. for providing lake-gauge data. J. Normandeau of SAO performed the preliminary\nGPS data analysis. BARGEN was installed and is maintained with the assistance of the UNAVCO Facility. We thank B. Bills and an anonymous reviewer for helpful comments on the manuscript. (B. Bills provided information regarding mining activities.) This research was supported by NSF grants EAR-9725766 and EAR-0135457, NASA grants NAG5-11629\nand NAG5-8226, USGS grant 99HQGR0212, the California Institute of Technology, and the Smithsonian Institution.", revision_no = "12", abstract = "Two sites of the BARGEN GPS network are located ∼30 km south of Great Salt Lake (GSL). Lake-level records since mid-1996 indicate seasonal water elevation variations of ∼0.3 m amplitude superimposed on a roughly “decadal” feature of amplitude ∼0.6 m. Using an elastic Green's function and a simplified load geometry for GSL, we calculate that these variations translate into radial crustal loading signals of ±0.5 mm (seasonal) and ±1 mm (decadal). The horizontal loading signals are a factor of ∼2 smaller. Despite the small size of the expected loading signals, we conclude that we can observe them using GPS time series for the coordinates of these two sites. The observed amplitudes of the variations agree with the predicted decadal variations to <0.5 mm. The observed annual variations, however, disagree; this difference may be caused by some combination of local precipitation-induced site motion, unmodeled loading from other nearby sources, errors in the GSL model, and atmospheric errors.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47372, title ="Assessing vertical axis rotations in large-magnitude extensional settings: A transect across the Death Valley extended terrane, California", author = "Petronis, Michael S. and Geissman, John W.", journal = "Journal of Geophysical Research B", volume = "107", number = "B1", pages = "Art. No. 2010", month = "January", year = "2002", doi = "10.1029/2001JB000239", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-143226413", note = "© 2002 The American Geophysical Union.\n\nReceived 11 September 2000; Revised 7 May 2001; Accepted 14 July 2001; Published 18 January 2002.\n\nWe thank Ren Thompson for use of his\nunpublished map of the central Death Valley extended terrane, John Miller\nand Dave Schneider for assistance sampling in sometimes inhospitable\nconditions, Zeke Snow for useful comments on a very early version of the\nmanuscript, and the National Park Service for (limited) permission to work\nin Death Valley, California. Funded in part by a NSF grant (Wernicke and\nGeissman) and an American Chemical Society Grant (Holm). We greatly\nappreciate the efforts of the reviewers, Mark Hudson and Jon Hagstrum,\nwhich greatly clarified and improved an earlier version of the manuscript.", revision_no = "9", abstract = "Models for Neogene crustal deformation in the central Death Valley extended terrane, southeastern California, differ markedly in their estimates of upper crustal extension versus shear translations. Documentation of vertical axis rotations of range-scale crustal blocks (or parts thereof) is critical when attempting to reconstruct this highly extended region. To better define the magnitude, aerial extent, and timing of vertical axis rotation that could mark shear translation of the crust in this area, paleomagnetic data were obtained from Tertiary igneous and remagnetized Paleozoic carbonate rocks along a roughly east-west traverse parallel to about 36°N latitude. Sites were established in ∼7 to 5 Ma volcanic sequences (Greenwater Canyon and Brown's Peak) and the ∼10 Ma Chocolate Sundae Mountain granite in the Greenwater Range, ∼8.5 to 7.5 Ma and 5 to 4 Ma basalts on the east flank of the Black Mountains, the 10.6 Ma Little Chief stock and upper Miocene(?) basalts in the eastern Panamint Mountains, and Paleozoic Pogonip Group carbonate strata in the north central Panamint Mountains. At the site level, most materials yield readily interpretable paleomagnetic data. Group mean directions, after appropriate structural corrections, suggest no major vertical axis rotation of the Greenwater Range (e.g., D = 359°, I = 46°, α_(95) = 8.0°, N = 12 (7 normal (N), 5 reversed (R) polarity sites)), little post-5 Ma rotation of the eastern Black Mountains (e.g., D = 006°, I = 61°, α_(95) = 4.0°, N = 9 N, 6 R sites), and no significant post-10 Ma rotation of the Panamint Range (e.g., D = 181°, I = −51°, α_(95) = 6.5°, N = 9 R sites). In situ data from the Greenwater Canyon volcanic rocks, Chocolate Sundae Mountain granite, Funeral Peak basalt rocks, the Little Chief stock, and Paleozoic carbonate rocks (remagnetized) are consistent with moderate south east-side-down tilting of the separate range blocks during northwest directed extension. The paleomagnetic data reported here suggest that the Panamints shared none of the 7 Ma to recent clockwise rotation of the Black Mountains crystalline core, as proposed in recent models for transtensional development of the central Death Valley extended terrane.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47383, title ="Discussion and reply: Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada", author = "Brady, Robert J. and Wernicke, Brian", journal = "Geological Society of America Bulletin", volume = "114", number = "1", pages = "126-128", month = "January", year = "2002", doi = "10.1130/0016-7606(2002)114<0126:R>2.0.CO;2 ", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140722-082949263", note = "© 2002 Geological Society of America.\n\nManuscript received by the Society March 27, 2001; Manuscript accepted May 16, 2001.", revision_no = "11", abstract = "In the canonical cross-sectional reconstruction\nof relationships at Yerington (Proffett,\n1977, Fig. 15), approximately two-thirds of\n~65° of rotation of Tertiary strata occurs on\na first generation of faults, the remaining third\n(20°–25°) occurring on later generations of\ncrosscutting faults. Given the lack of evidence\nfor multiple generations of faults in the South\nVirgin Mountains, we sought to critically\nevaluate this interpretation, which we cited as\nan example of multiple-domino-style normal\nfaulting, and assess whether published data require\nthe first set of faults to have deactivated\nat dips of 30°, or instead permit them to have\nremained active near their current dips of 10°–\n20°. Our reinterpretation of one of Proffett’s\ncross sections (Brady et al., 2000, Fig. 15B)\ndepicts the second generation of faults as having\nrelatively little displacement, and as having\nslipped synchronously with the first\ngeneration.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47345, title ="Distribution and provenance of the middle Miocene Eagle Mountain Formation, and implications for regional kinematic analysis of the Basin and Range province", author = "Niemi, Nathan A. and Wernicke, Brian P.", journal = "Geological Society of America Bulletin", volume = "113", number = "4", pages = "419-442", month = "April", year = "2001", doi = "10.1130/0016-7606(2001)113<0419:DAPOTM>2.0.CO;2", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-144124092", note = "© 2001 Geological Society of America. \n\nManuscript Received by the Society March 30, 2000; Manuscript Accepted April 19, 2000. \n\nThis research was supported by National Science\nFoundation (NSF) grants EAR-93–16797 and EAR-96–14780 (to Wernicke), EAR-95–26859 (to Saleeby),\nand an NSF Graduate Fellowship (to Niemi).\nDiscussions and field excursions with S. Beard, R.\nBohannon, J. Calzia, I. Cemen, H.D. Curry, K.\nFowler, C.J. Fridrich, J. Friedmann, W. Hamilton,\nK.V. Hodges, M.R. McMackin, T.L. Pavlis, A.R.\nPrave, P. Ryder, J.K. Snow, L. Serpa, L.T. Silver,\nC.H. Stevens, D.J. Topping, B.W. Troxel, J.D.Walker,\nand L.A. Wright have contributed to the ideas\npresented here, but they are in no way liable for any\nerrors in fact and interpretation. We thank Neil A.\nNiemi and J.A. Grover for field assistance and J.K.\nSnow, D.L. Lux, and L.A. Wright for providing\ncopies of their manuscripts prior to publication.\nConstructive reviews by W. Taylor and an anonymous\nreader greatly improved the clarity and presentation\nof this manuscript. Stereonet and MacStrat\nby R.W. Allmendinger were used for the analysis\nand plotting of data.", revision_no = "16", abstract = "Conglomeratic strata from middle Miocene sections in the central Resting Spring Range and nearby Eagle Mountain, California, contain a clast assemblage including marble, orthoquartzite, fusulinid grainstone, and coarse (∼1 m) monzogabbro, interstratified with tephras yielding laser-fusion ^(40)Ar/^(39)Ar ages of 11.6, 13.4, and 15.0 Ma. Petrographic and geochronologic evidence ties the clast assemblage to a source area in the southern Cottonwood Mountains, California, >100 km west-northwest of their present location. In the upper 100 m of the Resting Spring Range section, conglomerates are derived almost exclusively from the southern Cottonwoods source, and sandstone modes are as much as 50% angular plagioclase derived from the monzogabbro. The lack of dilution of this detritus by other sources and sedimentary features in both sections indicate (1) that deposition occurred on an alluvial fan with a north- northeast paleoslope and (2) that transport of the gravels by sedimentary processes was probably <20 km north-northeast, in a direction normal to the present azimuth to their source. Therefore, we interpret most or all of the net east-southeast transport as a result of extensional and strike-slip faulting between the Cottonwood Mountains and the Resting Spring Range since 11–12 Ma. Restoration of these deposits to a position 10–20 km north-northeast of the eastern margin of the monzogabbro source (east margin of the Hunter Mountain batholith) yields a net tectonic displacement of the Cottonwood Mountains relative to the Resting Spring Range of 104 km N67°W. This result confirms previous reconstructions based on the restoration of isopachs in the Cordilleran miogeocline, pre-Cenozoic structural features, and other proximal Tertiary deposits in the region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35442, title ="Paleo-Geomorphology of the Sierra Nevada, California, from (U-TH)/He Ages in Apatite", author = "House, Martha A. and Wernicke, Brian P.", journal = "American Journal of Science", volume = "301", number = "2", pages = "77-102", month = "February", year = "2001", doi = "10.2475/ajs.301.2.77 ", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121113-153928813", note = "© 2001 by American Journal of Science. We wish to thank the people at Yosemite and Sequoia-Kings Canyon National\nParks for making the necessary sample collection possible. We also thank J. Kelley of El\nAero for assistance in collection of the T2 transect. Funding for this study was provided\nby the National Science Foundation (EAR-9909453 to Wernicke; EAR-9633381 and\nEAR-9526895 to Wernicke and Farley). This manuscript benefited greatly from thoughtful\nreviews by P. Reiners, J. Spotila, and J. Wakabayashi.", revision_no = "12", abstract = "New apatite (U-Th)/He ages from the central Sierra Nevada, California, place limits on the morphology and evolution of longitudinal profiles of major transverse river drainages developed in the Late Cretaceous. Helium ages from a new orogen-parallel, constant-elevation sample transect are relatively uniform (∼60 Ma) and not correlated with topography, unlike those from a similar, lower elevation transect approx 15 km to the west. We interpret the marked difference in the two orogen-parallel profiles to reflect a headward decrease in long-wavelength, transverse relief at the time of cooling, consistent with either a concave-up stream gradient, typical of those observed near the headwaters of modern Sierran trunk streams, or a convex gradient like those found along slope breaks of eroding plateau edges. From the San Joaquin drainage we obtained a new helium age-versus-elevation profile, which has a comparable slope to those previously reported for the Yosemite Valley, Kings Canyon, and Mt. Whitney areas. This new profile yields slightly older ages at a given elevation as expected from its position adjacent to the largest major drainage. The age versus elevation profiles imply that the mean denudation rate of the region in the Cenozoic was about 0.04 to 0.05 mm/yr. We show that long-wavelength (λ = 70 km) relief inferred from longitudinal helium age variations is a strong function of erosion rate, such that even relatively subdued relief is detectable with helium age profiling provided that denudation rates were low. Using the rate implied by Sierran age-versus-elevation profiles, we infer long-wavelength relief of 1500 ± 500 m in the Late Cretaceous. By analogy with modern orogenic plateaus, this value of long-wavelength relief suggests a Cretaceous interior Cordilleran plateau lay at an elevation of at least 3000 m. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47415, title ="Cenozoic tectonism in the central Basin and Range; magnitude, rate, and distribution of upper crustal strain", author = "Snow, J. Kent and Wernicke, Brian P.", journal = "American Journal of Science", volume = "300", number = "9", pages = "659-719", month = "November", year = "2000", doi = "10.2475/ajs.300.9.659 ", issn = "0002-9599", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-084027038", note = "© 2000 American Journal of Science.\n\nThis research was supported by National Science Foundation Grants EAR 93-16797 and EAR-96-14780 awarded to B. Wernicke. We are grateful to our many\ncolleagues working in the central Basin and Range region for discussions and insights\nand to reviewers Roy K Dokka and Jon E. Spencer for improving the presentation.", revision_no = "11", abstract = "A wealth of pre-Cenozoic geologic markers across the central Basin and\nRange province, defined mainly by thrust faults developed within a miogeoclinal\nwedge, makes it one of the best areas on Earth to reconstruct large-scale continental\nextension. We use this ~100,000 km^2 region, bounded by the southern Sierra Nevada\non the west and the Colorado Plateau on the east, to illustrate the concepts of\ncorrelation and misalignment for regional strain markers and of strain compatibility\nand kinematic viability in palinspastic reconstructions. The results indicate ~250 to\n300 km of west-northwest motion of the Sierra away from the Plateau, accommodated\nby both crustal thinning and north-south shortening. Tertiary intermontane basin\ndeposits and mineral cooling ages of deeply exhumed rocks constrain the overall\nkinematics of motion. Most of the westward motion occurred between 16 and 5 Ma, at\nrates near 2 cm/yr, slowing to 1 to 1.5 cm/yr in the last 5 Ma. We have quantified the\npartitioning of strain between vertical crustal thinning (via normal faults) and map-view\nplane strain (via conjugate strike-slip faults) by placing a grid of 10 x 10 km\nelements on a retrodeformed map of the region and measuring the increase in area of\ngrid elements between the undeformed and present-day grids. This analysis yields a\nmaximum finite elongation of the Basin and Range at 36°N to 37°N of 3.4, oriented\nN73°W. Map-view area balance shows that 20 percent of this elongation is compensated\nby ~north-south shortening, and 80 percent by crustal thinning. This yields an\naverage thinning factor for the upper crust of 2.7 between the Sierra and Plateau,\ninconsistent with the hypothesis that Neogene deformation in the central Basin and\nRange is predominantly dextral-shear plane strain. These results, in concert with the\nobservation that the southern Sierra Nevada has similar crustal thickness to the central\nBasin and Range, support the hypothesis of large-scale eastward flow of Sierran deep\ncrust during extension.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/68933, title ="Dynamics of Plate Boundary Fault Systems from Basin and Range Geodetic Network (BARGEN) and Geologic Data", author = "Wernicke, Brian and Friedrich, Anke M.", journal = "GSA Today", volume = "10", number = "11", pages = "1-7", month = "November", year = "2000", issn = "1052-5173", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160708-143049038", note = "© 2000 Geological Society of America. \n\nManuscript received July 4, 2000; accepted September 6, 2000. \n\nBARGEN research is conducted under the auspices of the National Science Foundation’s Continental Dynamics Program, the U.S. Department of Energy’s Yucca Mountain Project, and NASA’s Solid Earth and Hazards Program, with design and maintenance assistance from the University Navstar Consortium (UNAVCO) Facility in Boulder, Colorado, the University of Nevada, Reno, and the University of Utah. We thank Gene Humphreys, Wayne Thatcher, and Karl Karlstrom for many useful suggestions on the manuscript.", revision_no = "11", abstract = "Continuously recorded Global Positioning\nSystem (GPS) data from the\nnorthern Basin and Range suggest that\ncontemporary deformation is quite slow\nand broadly distributed, rather than\nbeing concentrated in the relatively narrow\nzones of historical earthquakes. Surprisingly,\nhowever, in north-central\nNevada, the data indicate rapid, rangenormal\ncrustal shortening at a rate of\n2–3 mm/yr in an area where the geology\nindicates crustal extension via\nHolocene normal faulting. A possible\nexplanation for the conflicting geodetic\nand geologic data is that the region of\nshortening represents the contractile\nside of a slowly east-propagating deformation\npulse generated by the 1915\nPleasant Valley and 1954 Dixie Valley\nand Fairview Peak earthquakes. Such\npulses, which are transient effects not\nrecorded by faulting, are predicted by a\nbroad class of physical models, but have\nonly been observed within a few years\nafter very large earthquakes, when the\nsignal is much larger than the long-term\ndeformation rate. The Basin and Range,\nand similar areas with a combination of\nlow long-term deformation rates and\nlarge earthquakes, may therefore have\nthe best potential by combining modern\ngeologic and geodetic data to elucidate\nfault system behavior, in particular\nhow transient effects from an earthquake\non one fault may influence patterns\nof stress and seismic strain release\non others. These types of data are essential\nin developing realistic models of\nseismic hazard, and in linking\nshort–time scale observations with\nlonger term geologic processes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1101, title ="Results of the Basin and Range Geoscientific Experiment (BARGE): A marine-style seismic reflection survey across the eastern boundary of the central Basin and Range Province", author = "Brady, Robert and Wernicke, Brian", journal = "Geochemistry, Geophysics, Geosystems", volume = "1", number = "9", pages = "2000GC000078", month = "September", year = "2000", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:BRAggg00", note = "Copyright 2000 by the American Geophysical Union. \n\nReceived April 21, 2000; Revised July 28, 2000; Accepted August 18, 2000; Published September 22, 2000.", revision_no = "7", abstract = "Approximately 120 km of marine-style deep seismic reflection data were shot during a survey on the waters of Lake Mead in southeastern Nevada. The survey extends from near the abrupt eastern edge of the Basin and Range Province (BRP) to a point ~80 km into the extended domain. Data quality throughout the survey ranged from fair to poor; the recorded data include significant towing noise and occasionally problematic diffractions and sideswipe from canyon walls. The upper 2–4 s of the data shows well-defined reflections from sedimentary fill, but below that point, reflectivity is weak. Lower crustal reflectivity is generally absent under the eastern part of the survey, with a slight increase in reflectivity to the west. The reflection Moho appears as a series of weakly defined, discontinuous reflections, most of which occur at 10–11 s. A particularly interesting feature of the data set is the relative lack of reflectivity from the lower crust, which is a region of strong reflectivity on other seismic reflection data sets from the BRP.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47382, title ="Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada", author = "Brady, Robert and Wernicke, Brian", journal = "Geological Society of America Bulletin", volume = "112", number = "9", pages = "1375-1397", month = "September", year = "2000", doi = "10.1130/0016-7606(2000)112<1375:KEOALO>2.0.CO;2 ", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140722-082348906", note = "© 2000 Geological Society of America.\n\nManuscript received by the Society June 15, 1998; Revised manuscript received August 20, 1999; Manuscript accepted September 17, 1999.\n\nThis research was supported by National\nScience Foundation grant EAR-96-28262. We\nthank G. Spinelli and M. Herrin for field assistance.\nDiscussions and field excursions with\nL.S. Beard, K. Howard, J. Faulds, and S.\nRowland have contributed to the ideas presented\nhere, although they are in no way liable\nfor any errors in fact or interpretation. Stereonet\nby R.W. Allmendinger was used for the\nanalysis and plotting of data. Constructive and thoughtful reviews by James Faulds and L.\nSue Beard improved the manuscript.", revision_no = "13", abstract = "The South Virgin Mountains and Grand Wash trough comprise a mid-Miocene normal fault system that defines the boundary between the unextended Colorado Plateau to the east and highly extended crust of the central Basin and Range province to the west. In the upper 3 km of the crust, the system developed in subhorizontal cratonic strata in the foreland of the Cordilleran fold and thrust system. The rugged topography and lack of vegetation of the area afford exceptional three-dimensional exposures. Compact stratigraphy and well-defined prefaulting configuration of the rocks permitted a detailed reconstruction of the system. Reconstruction of cross sections based on more than 300 km2 of detailed mapping at a scale of 1:12\u200a000 shows that the fault system accommodated more than 15 km of roughly east-west–directed Miocene extension. Extension was initially accommodated on moderately to steeply dipping listric normal faults. As the early faults and fault blocks tilted, steeply to moderately dipping faults initiated within the fault blocks, soling into the early faults. Some of the early faults were active at dips of <20°. Isostatically driven tilting is superimposed on tilting due to active slip and domino-style rotation of the fault blocks. Collectively these processes rotated originally steeply dipping faults to horizontal orientations. The kinematics are inconsistent with the widely accepted view that many near-horizontal normal faults were rotated to their present orientations by later, crosscutting normal faults. However, reexamination of other areas suggests that the evolutionary sequence seen in the South Virgin Mountains may, in fact, be widely applicable.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35428, title ="Helium and argon thermochronometry of the Gold Butte\nblock, south Virgin Mountains, Nevada", author = "Reiners, Peter W. and Brady, Robert", journal = "Earth and Planetary Science Letters", volume = "178", number = "3-4", pages = "315-326", month = "May", year = "2000", doi = "10.1016/S0012-821X(00)00080-7", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121113-112406976", note = "© 2000 Elsevier Science B.V. Received 19 November 1999; received in revised form 13 March 2000; accepted 13 March 2000. ", revision_no = "14", abstract = "One of the largest exposures of Precambrian crystalline rock in the Basin and Range province of the southwestern USA is the Gold Butte block of the south Virgin Mountains, about 15 km west of the Colorado Plateau. It has been interpreted as a largely continuous crustal cross-section about 15–20 km thick that was exhumed by a deeply penetrating normal fault during Miocene extension. To test this interpretation as well as the use of the newly developed titanite (U–Th)/He thermochronometer, we examined the low temperature thermal history of the Gold Butte block with the apatite and titanite (U–Th)/He and muscovite ^(40)Ar/^(39)Ar thermochronometers. Apatite He ages average 15.2±1.0 (2σ) Ma throughout the block, indicating that the entire section was warmer than 70°C prior to Miocene exhumation. Titanite He ages increase from 18.6±1.5 Ma near the paleobottom (west) end of the block, to 195±15 Ma near the paleotop (east) end. A rapid change from mid-Tertiary to increasingly older titanite He ages to the east is observed at about 9.3 km paleodepth, and is interpreted as a fossil He partial retention zone for titanite. Assuming a pre-exhumation geotherm of 20°C/km (consistent with earlier apatite fission track work), this depth would have corresponded to 196°C prior to exhumation, indicating that laboratory-derived He diffusion characteristics for titanite that yield a closure temperature of about 200°C are applicable and correct. Muscovite ^(40)Ar/^(39)Ar ages are 1.0–1.4 Ga near the paleotop of the block, and 90 Ma near the paleobottom. Together with ^(207)Pb/^(206)Pb ages on apatite and titanite, and an earlier apatite fission track transect across the Gold Butte block, our data indicate that the continental crust at the western edge of the Colorado Plateau resided at moderate geothermal gradients (and slowly declined in temperature) from 1.4 Ga to about 100–200 Ma. A 90 Ma cooling event clearly affected the mid-crust (deepest portions of Gold Butte), which may reflect accelerated cooling or a brief heating and cooling cycle at this time, after which gradients returned to about 20°C/km prior to rapid exhumation in the Miocene. This work thus supports previous structural and thermochronologic studies that suggest that the Gold Butte block is the thickest largely continuous cross-section of crust exposed in the southwestern USA.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47429, title ="Present-day pattern of Cordilleran deformation in the western United States", author = "Bennett, R. A. and Davis, J. L.", journal = "Geology", volume = "27", number = "4", pages = "371-374", month = "April", year = "1999", doi = "10.1130/0091-7613(1999)027<0371:PDPOCD>2.3.CO;2 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-131153975", note = "© 1999 Geological Society of America.\n\nManuscript received September 25, 1998;\nRevised manuscript received December 21, 1998;\nManuscript accepted January 7, 1999.\n\nWe thank R. Bürgmann, P. Elósegui, E. Humphreys,\nand an anonymous referee for constructive reviews. We\nmade extensive use of data products from the BARD,\nCORS, IGS, and SCIGN networks (see Table 1) provided\nby the SOPAC facility. We are particularly grateful\nto R. Reilinger for the STRC data, and to R. King\nand S. McClusky for the analyses of the STRC data.\n(These data are also part of the SCEC data set.) We\nthank the many individuals and institutions contributing\nto the establishment and day-to-day operation of all of\nthe GPS networks that we used, including IGS, NOAA,\nthe Canadian Geological Survey and Canadian Geodetic\nSurvey, JPL, MIT, Caltech, the STRC consortium,\nthe Yucca Mountain–Death Valley consortium,\nUNAVCO, Scripps Institution of Oceanography, the\nUSGS, the Seismological Laboratory of UC Berkeley,\nand Trimble Navigation, Inc. We also made use of VLBI\ndata products (from terrestrial reference frame solution\nnumber 1083c) provided by the NASA GSFC. Topography\ndata are from NOAA. Figures were created with\nthe GMT software. This research was funded by\nNational Science Foundation grants EAR 94-18784 and\nEAR 95-12212, Nuclear Regulatory Commission grants\nNRC-04-92-071 and NRC-02-93-005, the California\nInstitute of Technology, and the Smithsonian Institution.", revision_no = "13", abstract = "We present the first detailed geodetic image of the entire western United States south of lat 42°N, merging both campaign and continuous Global Positioning System (GPS) and very long baseline interferometry (VLBI) data sets in a combined solution for station velocities having a single, uniform reference frame. The results are consistent with a number of features previously observed through local geodetic studies and very sparse space geodetic studies, including a dominant pattern of right-lateral shear associated with the San Andreas fault, rates of the westernmost sites (along the California coast) of 46–48 mm/yr relative to a North America reference frame, and some 11–13 mm/yr of deformation accommodated east of the Sierra Nevada in the Basin and Range province north of lat 36°N. South of 36°N, the solution also shows that the southernmost San Andreas fault system accommodates effectively all interplate motion and that the southern Basin and Range is not deforming significantly. At lat 37°N, the eastern California shear zone appears to exhibit simple shear oriented between ∼N20°W and ∼N40°W relative to North America, with a fairly well defined transition zone from localized shear to diffuse spreading in the Basin and Range. Enigmatically, this transition involves a significant component of contraction normal to the overall shear-zone trend; sites in the Great Basin move southwestward at up to ∼5 mm/yr toward sites within the eastern California shear zone. To the north, in contrast, there appears to be a relatively smooth transition from east-west spreading within the eastern Great Basin to northwest-southeast shear across the westernmost Basin and Range.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47418, title ="Deep burial of the footwall of the northern Snake Range decollement, Nevada", author = "Lewis, Claudia J. and Wernicke, Brian", journal = "Geological Society of America Bulletin", volume = "111", number = "1", pages = "39-51", month = "January", year = "1999", doi = "10.1130/0016-7606(1999)111<0039:DBOTFO>2.3.CO;2 ", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-093307164", note = "© 1999 Geological Society of America.\n\nManuscript received by the Society August 6, 1997; Manuscript accepted February 10, 1998.\n\nThis project was supported by National Science\nFoundation grants EAR 93-16797 and EAR 96-14780 (to Wernicke). We thank Matthew J. Kohn\nand Frank S. Spear for the computer codes used to\nrun the thermobarometric calculations.", revision_no = "12", abstract = "Metapelitic Eocambrian strata from eastern exposures of the footwall of the northern Snake Range decollement experienced Mesozoic amphibolite facies metamorphism and greenschist facies overprint accompanying extreme ductile thinning. Samples from the Hampton Creek area where the overprint is weakest contain the assemblage quartz + muscovite + biotite + garnet + plagioclase + opaque oxides + staurolite ± kyanite ± tourmaline ± apatite. Textural relations and consistency of rim analyses among multiple domains in each sample indicate equilibrium. Rim pressure-temperature estimates were obtained using the garnet-biotite Fe-Mg exchange thermometer and the garnet-muscovite-plagioclase-biotite and garnet-aluminosilicate-plagioclase barometers. The results suggest final equilibration at 610 ± 50 °C and 810 ± 70 MPa, or a depth of 30 ± 3 km, about a factor of 3 greater than the stratigraphic depth. \nTo the west, in the Schell Creek Range, correlative strata are contiguous with unmetamorphosed upper Paleozoic and Tertiary strata. From west to east, exposures of Eocambrian rocks in the two ranges collectively show increasing intensity of crystal-plastic deformation, metamorphic recrystallization, and metamorphic grade from subgreenschist to amphibolite facies, and a monotonic decrease in ^(40)Ar/^(39)Ar muscovite ages from Mesozoic age to about 23 Ma. In light of these relations, the pressure-temperature data suggest that Eocambrian strata were inclined eastward during Mesozoic metamorphism with ∼15–20 km of structural relief. We interpret the eastward tilting and burial to be the result of west-directed thrusting, as expressed by folding to the north in the Deep Creek Range. Unroofing of the deeply buried strata may have occurred partly in Cretaceous or early Cenozoic time, with final unroofing in Oligocene and Miocene time along the northern Snake Range decollement. These results exclude the hypothesis that the northern Snake Range decollement initiated as a brittle-ductile transition zone within Cambrian strata of a little-deformed miogeoclinal section, and support the hypothesis that it is a major low-angle extensional shear zone.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/52130, title ="Detecting Strain in the Yucca Mountain Area, Nevada", author = "Savage, J. C. and Connor, C. B.", journal = "Science", volume = "282", number = "5391", pages = "1007", month = "November", year = "1998", doi = "10.1126/science.282.5391.1007b", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141125-093015001", note = "© 1998 American Association for the Advancement of Science.\n\nReceived 9 June 1998; accepted 20 July 1998.", revision_no = "13", abstract = "From repeated surveys of the relative motions between geodetic stations Claim, Black, Mile, 67TJS, and Wahomie (Fig. 1) from 1991 through 1997, Wernicke et al. (1) deduce a N65°W strain accumulation rate of 50 ± 9 nanostrains per year (2) across the proposed high-level radioactive waste disposal repository at Yucca Mountain, Nevada. That strain rate is sufficient to indicate a higher-than-expected earthquake hazard at the repository. An earlier (1983–1993) U.S. Geological Survey (USGS) measurement (Table 1) of the strain accumulation in the network (black triangles) in Fig. 1 found a N65°W strain rate of 8 ± 20 nanostrains per year, a rate not significantly different from zero (3). Although the two measurements are marginally consistent at the 95% confidence level [that is, the difference 42 ± 22 nanostrains per year is less than 2 standard deviations, (SD)], the earthquake hazard implications are somewhat different. The USGS strain determination is the better of the two measurements. Wernicke et al. did not include the effects of monument instability in their error budget and, as a consequence, have significantly underestimated the uncertainties in their measurements. Moreover, in their interpretation of the data, they did not give proper weight to the coseismic and postseismic effects of the Little Skull Mountain earthquake (June 29, 1992, M = 5.4).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37969, title ="Dating topography of the Sierra Nevada, California, using apatite (U–Th)/He ages", author = "House, Martha A. and Wernicke, Brian P.", journal = "Nature", volume = "396", number = "6706", pages = "66-69", month = "November", year = "1998", doi = "10.1038/23926", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130416-111249596", note = "© 1998 Macmillan Publishers Ltd.\n\nReceived 10 December 1997; accepted 27 July 1998.\n\nThis work is part of the Southern Sierra Nevada Continental Dynamics Project,\nsupported by NSF's Continental Dynamics Program. We thank M. Ducea and J. Saleeby for permission to\ndiscuss their results before publication.", revision_no = "13", abstract = "The upward motion of rock masses relative to the Earth's surface has been documented for most of the main mountain belts using thermochronological and petrological techniques. More fundamental to the physical processes of mountain building, however, is the motion of the Earth's surface itself, which remains elusive. Here we describe a technique for estimating the age of topographic relief by mapping the low-temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium, thorium and helium contents. The technique exploits horizontal variations in temperature in the shallow crust that result from range-normal river drainages, because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges. Our results from the Sierra Nevada, California, indicate that two of the modern transverse drainages, the Kings and the San Joaquin, had developed deep canyons by the Late Cretaceous period, suggesting that the high topography of the range is ~50–60 million years older than generally thought.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47376, title ="Cenozoic Tectonism in the Central Basin and Range: Motion of the Sierran-Great Valley Block", author = "Wernicke, Brian and Snow, J. Kent", journal = "International Geology Review", volume = "40", number = "5", pages = "403-410", month = "May", year = "1998", doi = "10.1080/00206819809465217", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-151016860", note = "© 1998 by V. H. Winston & Son, Inc.", revision_no = "11", abstract = "According to geologic reconstructions, the motion of the Sierran-Great Valley block with respect to the Colorado Plateau was mainly westerly at more than 20 mm/yr from 16 to 10 Ma, changing to northwest or NNW since 8 to 10 Ma, at an average rate of 15 mm/yr. These kinematics are consistent with two other independent methods of determining the position of the block since 20 Ma–reconstructions based on paleomagnetic data from range blocks that bound the Basin and Range on the west, and a revised history of Pacific-North America plate motion based on a global plate circuit (Atwater and Stock, 1998, this issue). The plate-tectonic reconstruction shows a change to more northerly motion between the Pacific and North American plates at ∼8 Ma, in concert with the motion of the Sierran-Great Valley block. Moreover, the northeast limit of extant oceanic crust (as indicated by the reconstruction of the continental geology) tracks closely with the southwest limit of extant continental crust (as indicated by the positions of oceanic plates) since 20 Ma. The coordination between plate motions and the intraplate geology suggests that plate-boundary forces strongly influenced deformation within the continent.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48021, title ="Anomalous Strain Accumulation in the Yucca Mountain Area, Nevada", author = "Wernicke, Brian and Davis, James L.", journal = "Science", volume = "279", number = "5359", pages = "2096-2100", month = "March", year = "1998", doi = "10.1126/science.279.5359.2096 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140805-155615733", note = "© American Association for the Advancement of Science.\n\n29 October 1997; accepted 3 March 1998.\n\nWe thank J. Savage and M. Lisowski for providing trilateration data and GPS data and results from their 1993 survey, and J. Savage for useful discussions. The University NAVSTAR Consortium provided equipment and field logistical support. This project was funded by Nuclear Regulatory Commission contracts NRC-04-92-071 and NRC-02-93-005, and National Science Foundation grant EAR-94-\n18784.", revision_no = "13", abstract = "Global Positioning System (GPS) surveys from 1991 to 1997 near Yucca Mountain, Nevada, indicate west-northwest crustal elongation at a rate of 1.7 ± 0.3 millimeters per year (1σ) over 34 kilometers, or 50 ± 9 nanostrain per year. Global Positioning System and trilateration surveys from 1983 to 1997 on a 14-kilometer baseline across the proposed repository site for high-level radioactive waste indicate that the crust extended by 0.7 to 0.9 ± 0.2 millimeter per year (50 to 64 ± 14 nanostrain per year), depending on the coseismic effect of the M_s 5.4 1992 Little Skull Mountain earthquake. These strain rates are at least an order of magnitude higher than would be predicted from the Quaternary volcanic and tectonic history of the area.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48084, title ="Continuous GPS measurements of contemporary deformation across the northern Basin and Range province", author = "Bennett, R. A. and Wernicke, B. P.", journal = "Geophysical Research Letters", volume = "25", number = "4", pages = "563-566", month = "February", year = "1998", doi = "10.1029/98GL00128", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140806-115511813", note = "© 1998 American Geophysical Union.\n\nReceived July 3, 1997; revised December1 6, 1997; accepted December 30, 1997.\n\nThe University NAVSTAR Consortium (UNAVCO) facility assisted greatly in establishing the network. We thank the Seismological Laboratory at the University of Nevada, Reno, and particularly W. Nicks, for technical support and the University of Utah for assistance in site permitting. We also thank B. Frohring at Trimble Navigation Inc. who provided technical expertise. This manuscript benefited from careful reviews by J. Savage and an anonymous referee. We thank R. Smith and C. Meertens for keeping us abreast of their related research. Figures 1 and 2 were produced with the GMT software. This project is supported by NSF Grants EAR 94-18784, EAR 95-12212, Trimble Navigation Inc., the California Institute of Technology, and the Smithsonian Institution.", revision_no = "10", abstract = "We have acquired and analyzed data from the northern Basin and Range (NBAR) continuous GPS network since July 1996. The RMS residual with respect to the best fitting lines through the individual station position estimates is 2–3 mm in the horizontal and 6–10 mm in the vertical. After the first 395 days of operation, uncertainties in horizontal velocity estimates are 1–2 mm/yr (1-σ). Relative motion among NBAR sites located in eastern Nevada and in Utah is small, but east-west extension is significant assuming uniform strain accumulation across the whole network. The relative motion observed across the Wasatch fault zone is 2 ±2 mm/yr, east-west. Relative motions among stations in western Nevada and California, in contrast, are dominated by northwest, right-lateral shear. We infer an integrated deformation across the northern Basin and Range of 11 ± 2 mm/yr, northwest. These rates are consistent with previous geodetic measurements. Our GPS velocity estimates, however, reveal a possibly abrupt transition from east-west extension in eastern Nevada and Utah to right-lateral shear in western Nevada. This transition is roughly coincident with the central Nevada seismic belt and is consistent with the right-oblique focal mechanisms of the 1954 Dixie Valley and Fairview Peak earthquakes. The transition also appears to correlate spatially with a transition in upper mantle structure.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48085, title ="Global Positioning System constraints on fault slip rates in the Death Valley region, California and Nevada", author = "Bennett, R. A. and Wernicke, B. P.", journal = "Geophysical Research Letters", volume = "24", number = "23", pages = "3073-3076", month = "December", year = "1997", doi = "10.1029/97GL02951", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140806-115552261", note = "© 1997 American Geophysical Union.\n\nReceived April 14, 1997; revised September 29, 1997; accepted October 3, 1997.\n\nThis work was supported by Nuclear Regulatory Commission (NRC) Contracts NRC-04-92-071 and NRC-02-93-005, NSF Grant EAR-94-18784, and the Smithsonian Institution. The views and conclusions expressed in this paper do not represent an official regulatory position of the United States NRC. This manuscript benefited from careful reviews by E. Humphreys, R. Snay, and an anonymous referee, and useful discussions with J. Savage. Figures were created with the GMT software.", revision_no = "10", abstract = "We estimated horizontal velocities at 15 locations in the vicinity of Yucca Mountain, Nevada, from Global Positioning System surveys conducted between 1991 and 1996. We used these velocity estimates to infer slip rates on two major Quaternary faults within the eastern California shear zone (ECSZ), the Hunter Mountain and Death Valley faults. The sum of slip rates across the two faults is well determined at 5 ± 1 mm/yr (1-σ). Between 3 to 5 mm/yr of this motion appears to be accommodated along the Death Valley fault, implying 30–50 m of strain accumulation over the next 10,000 yr. If so, there is potential for 5 to 10 M_(w) 6.5–7.5 earthquakes during this period, a finding consistent with paleoseismological studies of the fault zone. Yucca Mountain, which lies 50 km east of the ECSZ, is the proposed location for the disposal of high-level nuclear waste in the United States.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35544, title ="Cenozoic thermal evolution of the central Sierra Nevada,\nCalifornia, from (U-Th)/He thermochronometry", author = "House, M. A. and Wernicke, B. P.", journal = "Earth and Planetary Science Letters", volume = "151", number = "3-4", pages = "167-179", month = "October", year = "1997", doi = "10.1016/S0012-821X(97)81846-8", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121119-113957873", note = "© 1997 Elsevier Science B.V. Received 28 March 1997; revised 10 July 1997; accepted 10 July 1997. This study was supported by National Science Foundation grants EAR-9526895, awarded to B. Wernicke, K. Farley, and J. Saleeby and EAR-9417939 to T. Dumitru. Constructive criticism by S. Peacock. C. Naeser, and an anonymous reviewer substantially improved the presentation of this\nmanuscript. [MK]", revision_no = "15", abstract = "Apatite(U-Th)/He cooling ages are reported for igneous apatite samples from the central Sierra Nevada and compared to published apatite fission track ages and track length data from the same mineral separates. Helium ages are youngest at low elevations and increase systematically toward higher elevations, ranging from 43 to 84 Ma at Yosemite Valley, 32 to 74 Ma at Kings River Canyon, and 23 to 75 Ma at Mt. Whitney. Helium ages from high elevation samples are generally concordant with corresponding fission track ages, while lower elevation helium ages are substantially younger. Cooling histories inferred from present laboratory derived fission track annealing and helium diffusion models do not match well, suggesting that either helium diffusion rates or fission track annealing rates are miscalibrated at temperatures below about 60°C for geologic exposure periods. Unlike the fission track results, the helium data do not indicate a very low geothermal gradient in the Sierra Nevada during early to middle Tertiary time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47426, title ="Intracrustal subduction and gravity currents in the deep crust: Sm-Nd, Ar-Ar, and thermobarometric constraints from the Skagit Gneiss Complex, Washington", author = "Wernicke, Brian and Getty, Stephen R.", journal = "Geological Society of America Bulletin", volume = "109", number = "9", pages = "1149-1166", month = "September", year = "1997", doi = "10.1130/0016-7606(1997)109<1149:ISAGCI>2.3.CO;2 ", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-111439136", note = "© 1997 Geological Society of America.\n\nManuscript received by the Society February 1, 1996; Revised manuscript received December 19, 1996; Manuscript accepted January 22, 1997.\n\nSupported by National Science Foundation\ngrants EAR-93-16797 awarded to Wernicke and\nEAR-93-16283 awarded to D. J. DePaolo. We\nare grateful for assistance from T. Johnson and\nB. J. Kriens in sample collection, J. L. Anderson\nin whole-rock chemical analysis, P. J. Wyllie in\ninterpreting igneous phase relations, M. Choudhury\nin mineral separations, J. A. Armstrong,\nP. A. Carpenter, M. A. House, and M. Peters in\nmicroprobe and scanning electron microscope\nmicroanalysis, J. B. Saleeby in zircon dissolutions,\nK. V. Hodges and T. Owen in mass spectrometry\nand data analysis, M. J. Kohn in thermobarometry,\nand D. J. Stevenson in the physics\nof gravity currents. S. Getty thanks D. J. DePaolo for the freedom to pursue this topic. Discussions\nwith B. J. Kriens, R. B. Miller, and\nR. A. Haugerud have stimulated this study. Detailed,\nconstructive reviews provided by D. L.\nWhitney and Bulletin reviewers R. A. Haugerud,\nC. A. Hopson, J. M. Mattinson, and J. K.\nMortensen greatly clarified the presentation.", revision_no = "13", abstract = "Isotopic and thermobarometric (pressure-temperature, P-T) data on a gneissic quartz diorite, combined with previous U-Pb ages and P-T data on wall-rock metapelites, define a precise P-T time series for a portion of the Skagit Gneiss Complex, a deep crustal crystalline complex within a zone of intracontinental collision. Concordant U-Pb and Sm-Nd ages on zircon indicate crystallization at 68 Ma, which preceded metamorphism of nearby pelitic wall rocks (garnet core assemblages) and the pluton (plagioclase-hornblende coronas on garnet) at ≈800–900 MPa, 700–800 °C. Following nearly isothermal decompression and sillimanite-cordierite metamorphism of wall rocks (garnet rims plus matrix) at 300–500 MPa, 650–700 °C, a Sm-Nd mineral isochron including two garnet separates records an initial phase of cooling of the complex at 60 Ma. Slow cooling (≈10 °C/m.y.) extends from approximately 60 Ma to 50 Ma. Hornblende and biotite Ar-Ar ages of 47 Ma and 45 Ma, respectively, define a second unroofing event; cooling rates during this period were approximately 100 °C/m.y. \nLate Cretaceous deep burial followed by two distinct unroofing episodes is also observed in some Cordilleran metamorphic core complexes and may suggest a common origin. We propose that regional shortening in the Cordilleran interior is accommodated by a process of intracrustal subduction, i.e., the upper crust is forced downward into a crustal asthenosphere, resulting in a cold, buoyant root. Heating and weakening of the root cause the formation of gravity currents, effective viscosity being in the range of 10^(16)–10^(19) Pa s, spreading outward below nonfluid upper crust. Spreading of the gravity current, which does not necessarily contribute to crustal thinning, is driven by the small density contrast between the root and its mid-crustal surroundings. Hence unroofing is neither a response to overthick crust nor controlled by the orientation of principal stress axes in the upper crust and upper mantle. The root then cools slowly until final unroofing to near-surface levels, which may occur via either extension or shortening with consequent erosion.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47434, title ="Reconciliation of San Andreas slip discrepancy by a combination of interior Basin and Range extension and transrotation near the coast", author = "Dickinson, William R. and Wernicke, Brian P.", journal = "Geology", volume = "25", number = "7", pages = "663-665", month = "July", year = "1997", doi = "10.1130/0091-7613(1997)025<0663:ROSASD>2.3.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-134650065", note = "© 1997 Geological Society of America. \n\nManuscript received January 10, 1997; Revised manuscript received April 4, 1997; Manuscript accepted April 15, 1997. \n\nPartial support for this work was provided by National Science Foundation grant EAR-94-18784 (to Wernicke). We thank the Caltech Geology Club for arranging a seminar at which our respective points of view were pointedly juxtaposed in a way that led us to blend them together. Jim Abbott of SciGraphics in Tucson, Arizona, prepared the figures.", revision_no = "11", abstract = "Measurements of net translation along the Neogene San Andreas transform boundary between Pacific and North American plates, as indicated by the global correlation of sea-floor magnetic anomalies and by total Neogene displacements along strands of the onshore San Andreas fault system, differ by hundreds of kilometres. The apparent motion discrepancy is reconciled for post–mid-Miocene time if both transrotational deformation along the coastal belt of California and basin-range extension east of the Sierra Nevada are taken into account.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47422, title ="Three-dimensional crustal structure of the southern Sierra Nevada from seismic fan profiles and gravity modeling", author = "Fliedner, Moritz M. and Ruppert, Stanley", journal = "Geology", volume = "24", number = "4", pages = "367-370", month = "April", year = "1996", doi = "10.1130/0091-7613(1996)024<0367:TDCSOT>2.3.CO;2 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140723-100821423", note = "© 1996 Geological Society of America.\n\nManuscript received August 21, 1995;\nRevised manuscript received December 21, 1995;\nManuscript accepted December 22, 1995.\n\nThe Southern Sierra Continental Dynamics project is\nsupported by the National Science Foundation (NSF)\ngrant EAR-91-19263 to Duke University; this work was\nsupported by NSF grants EAR-92-04998 and EAR-94-\n05577 to Stanford University and Department of Energy\ncontract W-7405-ENG-48 to Lawrence Livermore National\nLaboratory. The seismic data were collected with\nsupport from the U.S. Geological Survey and the Program\nfor Array Seismic Studies of the Continental Lithosphere (PASSCAL) and are available from the Incorporated\nResearch Institutions for Seismology (IRIS)\nData Management Center, via http://www.iris.washing\nton.edu/. We thank Tom Parsons and an anonymous reviewer\nfor helpful reviews.", revision_no = "15", abstract = "Traveltime data from the 1993 Southern Sierra Nevada Continental Dynamics seismic refraction experiment reveal low crustal velocities in the southern Sierra Nevada and Basin and Range province of California (6.0 to 6.6 km/s), as well as low upper mantle velocities (7.6 to 7.8 km/s). The crust thickens from southeast to northwest along the axis of the Sierra Nevada from 27 km in the Mojave Desert to 43 km near Fresno, California. A crustal welt is present beneath the Sierra Nevada, but the deepest Moho is found under the western slopes, not beneath the highest topography. A density model directly derived from the crustal velocity model but with constant mantle density satisfies the pronounced negative Bouguer anomaly associated with the Sierra Nevada, but shows large discrepancies of >50 mgal in the Great Valley and in the Basin and Range province. Matching the observed gravity with anomalies in the crust alone is not possible with geologically reasonable densities; we require a contribution from the upper mantle, either by lateral density variations or by a thinning of the lithosphere under the Sierra Nevada and the Basin and Range province. Such a model is consistent with the interpretation that the uplift of the present Sierra Nevada is caused and dynamically supported by asthenospheric upwelling or lithospheric thinning under the Basin and Range province and eastern Sierra Nevada.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/34893, title ="Origin of High Mountains in the Continents: The Southern Sierra Nevada", author = "Wernicke, Brian and Clayton, Robert", journal = "Science", volume = "271", number = "5246", pages = "190-193", month = "January", year = "1996", doi = "10.1126/science.271.5246.190", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121015-105100386", note = "© 1996 American Association for the Advancement of Science. 30 August 1995; accepted 14 November 1995. Supported by the Continental Dynamics Program of\nthe National Science Foundation (EAR-9120690 to\nS.P., EAR-9120688 to G.J., EAR-9119263 to P.M.,\nand EAR-9120689 to R.P.), the Department of Energy\n(DE-FG03-93ER14311 to R.C.), the U.S. Navy (China\nLake Naval Weapons Center), and the U.S. Air Force\n(Office of Scientific Research). Key logistical support\nwas provided by the National Park Service, Bureau of\nLand Management, and U.S. Forest Service.", revision_no = "20", abstract = "Active and passive seismic experiments show that the southern Sierra, despite standing 1.8 to 2.8 kilometers above its surroundings, is underlain by crust of similar seismic thickness, about 30 to 40 kilometers. Thermobarometry of xenolith suites and magnetotelluric profiles indicate that the upper mantle is eclogitic to depths of 60 kilometers beneath the western and central parts of the range, but little subcrustal lithosphere is present beneath the eastern High Sierra and adjacent Basin and Range. These and other data imply the crust of both the High Sierra and Basin and Range thinned by a factor of 2 since 20 million years ago, at odds with purported late Cenozoic regional uplift of some 2 kilometers.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47347, title ="Low-angle normal faults and seismicity: A review", author = "Wernicke, Brian", journal = "Journal of Geophysical Research B", volume = "100", number = "B10", pages = "20159-20174", month = "October", year = "1995", doi = "10.1029/95JB01911", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-145013941", note = "© 1995 American Geophysical Union.\n\nReceived August 26, 1994; revised June 13, 1995; accepted Jun 20, 1995.\n\nPaper number 95JB01911.\nDiscussions with D. L. Anderson and H. Kanamori helped clarify my thinking on seismological apects of this paper. Reviews by G. A. Davis, R. K. Dokka, J. W. Geissman, T. A.\nHauge, B. E. John, and JGR reviewers D. Davis, J. Oldow, and an anonymous referee contributed substantially toward improving the presentation. This research was supported by NSF grants EAR-9219939 and EAR-9316797.", revision_no = "10", abstract = "Although large, low-angle normal faults in the continental crust are widely recognized, doubts persist that they either initiate or slip at shallow dips (<30°), because (1) global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30° and (2) Andersonian fault mechanics predict that normal faults dipping less than 30° cannot slip. Geological reconstructions, thermochronology, paleomagnetic studies, and seismic reflection profiles, mainly published in the last 5 years, reinforce the view that active low-angle normal faulting in the brittle crust is widespread, underscoring the paradox of the seismicity data. For dip-slip faults large enough to break the entire brittle layer during earthquakes (M_w ∼ 6.5), consideration of their surface area and efficiency in accommodating extension as a function of dip θ suggests average recurrence intervals of earthquakes R' ∝ tan θ, assuming stress drop, rigidity modulus, and thickness of the seismogenic layer do not vary systematically with dip. If the global distribution of fault dip, normalized to total fault length, is uniform, the global recurrence of earthquakes as a function of dip is shown to be R ∝ tan θ sin θ. This relationship predicts that the frequency of earthquakes with nodal planes dipping between 30° and 60° will exceed those with planes shallower than 30° by a factor of 10, in good agreement with continental seismicity, assuming major normal faults dipping more than 60° are relatively uncommon. Revision of Andersonian fault mechanics to include rotation of the stress axes with depth, perhaps as a result of deep crustal shear against the brittle layer, would explain both the common occurrence of low-angle faults and the lack of large faults dipping more than 60°. If correct, this resolution of the paradox may indicate significant seismic hazard from large, low-angle normal faults.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37447, title ="Near-Field Investigations of the Landers Earthquake Sequence, April to July 1992", author = "Sieh, Kerry and Jones, Lucile", journal = "Science", volume = "260", number = "5105", pages = "171-176", month = "April", year = "1993", doi = "10.1126/science.260.5105.171 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130311-145649896", note = "© 1993 American Association for the Advancement of Science. \n\nWe thank D. Agnew, A. Densmore, J. Dolan, K. Gross, D. Jackson, S. Larsen, M. Lisowski, M. Rymer, Z. Shen, and J. Svarc for helpful discussions and assistance. We also thank the seismic analysts of the Southern California Seismographic Network who have processed the Landers earthquake data, including R. Dollar, R. Geary, D. Given, W. Huston, S. Perry-Huston, R. Robb, and L. Wald. Data collection and processing partially supported by the Caltech Earthquake Research Affiliates Emergency Earthquake Fund and by the Southern California Earthquake Center (contribution number 25), which is funded by the National Science Foundation and the U.S. Geological Survey. Additional support from Division of Geological and Planetary Sciences, California Institute of Technology (contribution number 5217).", revision_no = "23", abstract = "The Landers earthquake, which had a moment magnitude (M_w) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M_w 6.1 preshock and M_w 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47370, title ="Large-magnitude Permian shortening and continental-margin tectonics in the southern Cordillera: Discussion and reply", author = "Stone, Paul and Stevens, Calvin H.", journal = "Geological Society of America Bulletin", volume = "105", number = "2", pages = "280-283", month = "February", year = "1993", doi = "10.1130/0016-7606(1993)105<0279:LMPSAC>2.3.CO;2", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-140141178", note = "© 1993 Geological Society of America.\n\nManuscript received by the Society July 7, 1992; Manuscript accepted July 7, 1992.\n\nFunding was provided by National Science Foundation grant\nEAR-92-04868.", revision_no = "12", abstract = "Stone and Stevens agree that apparent termination of large displacement\non the Last Chance thrust near the Darwin Plateau is a\nmajor problem to be explained by any viable model of Cordilleran\ngeology. Their arguments against a Permian age for thrusting, however,\nare deeply flawed. The alternative structural relations they advocate\nin the Darwin Plateau, southern Inyo Mountains, and northern\nDeath Valley areas result in a thrust belt that is not strain compatible—\nthat is, retrodeformable to its original state without gaps or overlaps\nin the reconstruction.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/48082, title ="Lithospheric Extension Near Lake Mead, Nevada: A Model for Ductile Flow in the Lower Crust", author = "Kruse, Sarah and McNutt, Marcia", journal = "Journal of Geophysical Research B", volume = "96", number = "B3", pages = "4435-4456", month = "March", year = "1991", doi = "10.1029/90JB02621", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140806-115436547", note = "© 1991 American Geophysical Union.\n\nReceived February 13, 1991; revised November 12, 1990.\n\nRoger Buck was generous with his time and made suggestions that considerably strengthened this work. His support is gratefully acknowledged. Constructive reviews by Jon Spencer and Kevin Furlong significantly improved the manuscript. This work was supported in part by NASA NAG 5-1084 to M.M.", revision_no = "11", abstract = "Small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions. In this study we examine the boundary between the unextended Colorado Plateau and a strongly extended domain in the Basin and Range Province in the Lake Mead (Nevada) region. Bouguer gravity and topography data suggest that both present and preextensional variations in crustal thickness between the unextended and extended regions are small. Analytic channel flow models show that viscosities required for ductile flow in a lower crustal channel to reduce discontinuities in crustal thickness associated with variable amounts of extension are highly dependent on the channel thickness and on the length scale of flow required. Finite element modeling of Newtonian flow and power law creep shows that flow over the length scale of the eastern Basin and Range (500 km or more) corresponding to upper crustal extension by a factor of 1.4–3 over 10 m.y. requires effective viscosities less than 10^(18)–10^(20) Pa s for ductile channels 10–25 km thick. Flow over shorter length scales (150 km) may be accommodated with effective viscosities as high as 10^(21) Pa s. Modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory-derived power law creep rates. The longer-scale flow may require elevated crustal temperatures (more than 700°C), depending on the composition and material properties assumed. Under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep. This work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions, and thereby explaining the relative uniformity in gravity and topography between such regions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47369, title ="Comment and Reply on \"Escape hypothesis for the Stikine block\"", author = "McGroder, Michael F. and Umhoefer, Paul J.", journal = "Geology", volume = "17", number = "12", pages = "1162-1163", month = "December", year = "1989", doi = "10.1130/0091-7613(1989)017<1161:CAROEH>2.3.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-133116492", note = "© 1989 Geological Society of America.", revision_no = "13", abstract = "When stratigraphic, geochemical, and faunal data of Wrangellia and\nWallowa-Seven Devils are viewed objectively, the data suggest—but do\nnot require—that the two crustal blocks developed adjacent to one\nanother. Sarewitz (1983) and Rusmore (1987) noted that the geochemical\ndifferences between the arclike Wallowa and Cadwallader volcanic rocks\nvs. the back-arclike Karmutsen volcanics on Wrangellia may be the result\nof their tectonic setting relative to the arc axis. We disagree with Mortimer's\n(1986) correlation of Wallowa volcanics with Stikinia volcanics\nbecause the subalkalic volcanic rocks of Wallowa are mainly Ladinian in\nage and compare poorly with the calc-alkalic augite porphyry of Carnian-\nNorian age that is typical of Stikine. Newton (1983) reported that Late Triassic molluscan fauna from the Wallowa terrane are most similar to\nthose collected from the Wrangell Mountains. As addressed below, paleomagnetic\ndata do not constrain Wallowa-Wrangellia-Stikine correlations.\nIt appears, therefore, that faunal ties and timing of volcanism\nindicate that the Wallowa terrane is more similar to Wrangellia than to\nStikine, and we incorporate this correlation into our model until direct\nevidence can support or deny it.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47368, title ="Escape hypothesis for the Stikine block", author = "Wernicke, Brian and Klepacki, David W.", journal = "Geology", volume = "16", number = "5", pages = "461-464", month = "May", year = "1988", doi = "10.1130/0091-7613(1988)016<0461:EHFTSB>2.3.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140721-132529814", note = "© 1988 Geological Society of America.\n\nManuscript received June 25, 1987;\nRevised manuscript received February 8, 1988;\nManuscript accepted February 18, 1988.\n\nSupported by National Science Foundation Grant\nEAR-8451181 to Wernicke and Grant EAR-7713637\nto B. C. Burchfiel; a grant from the Shaler and Clifford\nP. Hickock Junior Faculty Development Funds of\nHarvard University; and the Geological Survey of\nCanada. We thank J. O. Wheeler, B. C. Burchfiel,\nM. F. Folio, Karen Lund, J.W.H. Monger, and L. W.\nSnee for fruitful discussions. Careful reviews by M. T.\nBrandon and D. J. Tempelman-Kluit contributed\ngreatly to the clarification of ideas presented here.", revision_no = "12", abstract = "Comparison of stratigraphic, faunal, and paleomagnetic characteristics of the Stikine terrane of British Columbia with other terranes in the Cordilleran collage reveals broad similarities with a group of terranes that formed a volcanic belt marginal to North America in Paleozoic and early Mesozoic time. Unlike Stikine, these terranes lie inboard of another belt of terranes that represents an early Mesozoic subduction complex or melange belt. Thus, in British Columbia the marginal volcanic belt is apparently doubled. In the Columbia embayment region, the marginal volcanic and melange belts are missing, and rocks of the outermost major component of the collage, the Wrangellia superterrane, are juxtaposed directly against cratonic rocks. We propose that Stikine is the missing fragment from the Columbia embayment; its northward \"tectonic escape\" was driven by the early stages of collision of the Wrangefia superterrane with North America in Middle to Late Jurassic time. The escaped fragment was then trapped between melange and more northerly, later arriving parts of the Wrangellia superterrane in Early to mid-Cretaceous time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47324, title ="Structural discordance between neogene detachments and frontal Sevier thrusts, central Mormon Mountains, southern Nevada", author = "Wernicke, Brian and Walker, J. Douglas", journal = "Tectonics", volume = "4", number = "2", pages = "213-246", month = "February", year = "1985", doi = "10.1029/TC004i002p00213 ", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-103530197", note = "© 1985 by the American Geophysical Union.\n\nPaper number 4T0792.\n\nReceived May 10, 1984; accepted May 22, 1984.\n\nThe authors\nacknowledge support from NSF grants EAR 7713637 awarded to B.C. Burchfiel, EAR 7926346 awarded to B.C. Burchfiel and P.\nMolnar, and EAR 8319767 awarded to B. Wernicke.", revision_no = "10", abstract = "Detailed geologic mapping in the Mormon Mountains of southern Nevada provides significant insight into processes of extensional tectonics developed within older compressional orogens. A newly discovered, WSW-directed low-angle normal fault, the Mormon Peak detachment, juxtaposes the highest levels of the frontal most part of the east-vergent, Mesozoic Sevier thrust belt with autochthonous crystalline basement. Palinspastic analysis suggests that the detachment initially dipped 20–25° to the west and cut discordantly across thrust faults. Nearly complete lateral removal of the hanging wall from the area has exposed a 5 km thick longitudinal cross-section through the thrust belt in the footwall, while highly attenuated remnants of the hanging wall (nowhere more than a few hundred meters thick) structurally veneer the range. The present arched configuration of the detachment resulted in part from progressive “domino-style” rotation of a few degrees while it was active, but is largely due to rotation on younger, structurally lower, basement-penetrating normal faults that initiated at high-angle.\n\nThe geometry and kinematics of normal faulting in the Mormon Mountains suggest that pre-existing thrust planes are not required for the initiation of low-angle normal faults, and even where closely overlapped by extensional tectonism, need not function as a primary control of detachment geometry. Caution must thus be exercised in interpreting low-angle normal faults of uncertain tectonic heritage such as those seen in the COCORP west-central Utah and BIRP's MOIST deep-reflection profiles. Although thrust fault reactivation has reasonably been shown to be the origin of a very few low-angle normal faults, our results indicate that it may not be as fundamental a component of orogenic architecture as it is now widely perceived to be. We conclude that while in many instances thrust fault reactivation may be both a plausible and attractive hypothesis, it may never be assumed.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98818, title ="Uniform-sense normal simple shear of the continental lithosphere", author = "Wernicke, Brian", journal = "Canadian Journal of Earth Sciences", volume = "22", number = "1", pages = "108-125", month = "January", year = "1985", doi = "10.1139/e85-009", issn = "1480-3313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190924-075440069", note = "© 1985 NRC Research Press. \n\nReceived February 7, 1984; Revision accepted July 12, 1984. \n\nResearch leading to this report has been funded by National Science Foundation grants EAR 7713637 to B. C. Burchfiel. EAR 7926346 to B. C. Burchfiel and P. Molnar, and EAR 8219034 to B. P. Wernicke. Discussions with J. M. Bartley and R. J. O'Connell have greatly clarified for me some of the concepts upon which this paper is based. I thank P. C. England and J. M. Bartley for reviewing an early draft of this manuscript and R. A. Price and K. R. McClay for helpful, critical reviews of the penultimate draft.", revision_no = "9", abstract = "Geophysical studies suggest that the thin crust characteristic of the Basin and Range Province extends eastward beneath the west margin of the Colorado Plateau and Rocky Mountain regions. In Arizona and Utah, zones perhaps over 100\u2002km wide may be defined, bounded on the west by the east limit of upper crustal normal faults that account for more that 10% extension and on the east by the east limit of thinning beneath the Colorado Plateau. A discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning, assuming the \"discrepant zone\" crust was as thick as or thicker than the Colorado Plateau – Rocky Mountain crust prior to extensional tectonism.If various theories appealing to crustal erosion are dismissed, mass balance problems evident in the discrepant zones are most easily resolved by down-to-the-east normal simple shear of the crust, moving lower and middle crustal rocks that initially were within the zones up-and-to-the-west to where they now are locally exposed in the Basin and Range Province. West of the discrepant zones in both Arizona and Utah, east-directed extensional allochthons with large displacement are exposed. These geophysical and geological observations complement one another if it is accepted that the entire crust in both Arizona and Utah failed during extension on gently east-dipping, east-directed, low-angle normal faults and shear zones over a region several hundred kilometres wide.Large-scale, uniform-sense normal simple shear of the crust suggests the entire lithosphere may do the same. Such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear. In the case of the Arizona, Utah, and Red Sea extensional systems, and possibly the Death Valley extensional terrain, a broad topographic arch, typically 1500–2000\u2002m higher than the extended terrain, is present, suggesting lithospheric thinning in areas predicted by the hypothesis.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47274, title ="Comment and Reply on ‘Magnitude of crustal extension in the southern Great Basin’", author = "Royse, Frank and Wernicke, Brian", journal = "Geology", volume = "11", number = "8", pages = "496-497", month = "August", year = "1983", doi = "10.1130/0091-7613(1983)11<496:CAROMO>2.0.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140716-144507189", note = "© 1983 Geological Society of America.", revision_no = "17", abstract = "We thank Royse for explicitly raising a point that we did not\nmake completely clear in our paper: evidence that establishes a Tertiary\nage for the development of the Las Vegas shear zone. This is a\nproblem not only for the shear zone but for the Garlock fault as\nwell. In the case of both faults, the principal matching features across them which demonstrate large displacement and/or bending\nare of Mesozoic age or older, indicating that displacements could\nhave occurred during the Mesozoic.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47262, title ="A new type of decollement thrusting", author = "Burchfiel, B. Clark and Wernicke, Brian", journal = "Nature", volume = "300", number = "5892", pages = "513-515", month = "December", year = "1982", doi = "10.1038/300513a0 ", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140716-104344077", note = "© 1982 Macmillan Journals Ltd. \n\nReceived 28 June; accepted 24 September 1982. \n\nThis research has been supported by the NSF, the US Geological\nSurvey, Chevron USA, Mobil Oil Corporation, the Geological Society of America, and the Fannie and John Hertz Foundation.", revision_no = "12", abstract = "One of the fundamental rules of decollement tectonics is that decollement horizons form in mechanically weak layers. Here we document two examples of decollement-style thrust faults that detach within thick platformal dolostones in preference to apparently weaker layers of shale, siltstone and limestone underlying the dolostones. The thrusts are the Keystone–Muddy Mountain–Glendale thrust system (the KMG thrust system), , and the underlying Contact–Red Spring–North Buffiington–Mormon thrust system (the CRM thrust system), both of southern Nevada. They form part of the Sevier orogenic belt, and extend for roughly 250km along strike, together showing at least 65 km tectonic overlap (Fig. 1). Although the thrust systems are closely related spatially, the higher KMG system is younger than the underlying CRM thrust system, and the two developed essentially independently. Three points are important: first, that both the KMG and the CRM thrust systems are decollement style thrusts; second, that the decollement horizon is primarily restricted to a narrow stratigraphical interval within a bedded sequence of essentially homogeneous dolostones of the Middle Cambrian Bonanza King Formation; the third, that the thrust faults formed at a very shallow crustal level (<5 km).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47272, title ="Magnitude of crustal extension in the southern Great Basin", author = "Wernicke, Brian and Spencer, Jon E.", journal = "Geology", volume = "10", number = "10", pages = "499-502", month = "October", year = "1982", doi = "10.1130/0091-7613(1982)10<499:MOCEIT>2.0.CO;2 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140716-143803082", note = "© 1982 Geological Society of America.\n\nManuscript received December 28, 1981;\nRevised manuscript received May 25, 1982;\nManuscript accepted June 2, 1982.\n\nReviewed by R. E. Anderson, R. G. Bohannon,\nG. A. Davis. Dietrich Roeder, and L. A.\nWright. Supported by National Science Foundation\nGrants EAR 7913637 awarded to B. C.\nBurchfiel and EAR 7926346 awarded to B. C.\nBurchfiel and Peter Molnar.", revision_no = "13", abstract = "Strike-slip faults in the southern Great Basin separate areas of Cenozoic upper crustal extension from relatively stable tectonic blocks. Linear geologic features, offset along the Garlock fault, Las Vegas Valley shear zone, and Lake Mead fault system, allow reconstruction of the southern Great Basin to a pre-extension configuration. The Sierra Nevada, Mojave Desert, Spring Mountains, and Colorado Plateau are treated as stable, unextended blocks that have moved relative to each other in response to crustal extension, with the Spring Mountains held fixed to the Mojave block. Our reconstruction indicates a minimum of 65% extension (140 km) between the southern Sierra Nevada and Colorado Plateau.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47323, title ="Comment and Reply on ‘Mesozoic evolution, hinterland of the Sevier orogenic belt’ (Comment)", author = "Wernicke, Brian", journal = "Geology", volume = "10", number = "1", pages = "3-5", month = "January", year = "1982", doi = "10.1130/0091-7613(1982)10<3:CAROME>2.0.CO;2 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140718-102325114", note = "© 1982 Geological Society of America.\n\nI thank John Sharry, B. C. Burchfiel, and J. H. Willimen for criticism\nof this manuscript. This study was supported by National Science Foundation\nGrant EAR 7713637 awarded to B. C. Burchfiel.", revision_no = "11", abstract = "Allmendinger and Jordan (1981) have attempted to relate\nplutonism, metamorphism, and thrusting in the Cordillera by\ninterpreting selected features of the Sevier hinterland. Although\nthe pros and cons of their large-scale speculations have been previously\ndiscussed (Burchfiel and Davis, 1975; Hamilton, 1978), the\nspecifics of their Jurassic and Cretaceous scenario behind the\nthrust belt invite comment.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49099, title ="Modes of extensional tectonics", author = "Wernicke, Brian and Burchfiel, B. C.", journal = "Journal of Structural Geology", volume = "4", number = "2", pages = "105-115", month = "January", year = "1982", doi = "10.1016/0191-8141(82)90021-9 ", issn = "0191-8141", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140902-095759313", note = "© 1982 Pergamon Press Ltd.\n\nReceived 1 September 1981, accepted in revised form 10 March 1982.\n\nThis paper benefited from the critical reviews\nof R. E. Anderson, A. W. Bally, P. L. Hancock and James Helwig.\nWe thank M. S. Beaufait, R. G. Bohannon, G. A. Davis, R. K.\nDokka, E. G. Frost, P. L. Guth, W. B. Hamilton, L. Royden and T.\nJ. Shackleford for fruitful discussions. This work was supported by\nNSF Grant 7713637 awarded to B. C. Burchfiel and NSF Grant\nEAR7926346 awarded to B. C. Burchfiel and P. Molnar.", revision_no = "11", abstract = "Although hundreds of papers have been devoted to the geometric and kinematic analysis of compressional tectonic regimes, surprisingly little has been written about the details of large-scale strain in extended areas. We attempt, by means of quantitative theoretical analysis guided by real geological examples, to establish some ground rules for interpreting extensional phenomena. We have found that large, very low-angle normal faults dominate highly extended terranes, and that both listric and planar normal faults are common components of their hanging walls. The very low-angle normal faults may have displacements from a few kilometres up to several tens of kilometres and we regard their hanging walls as extensional allochthons, analogous (but with opposite sense of movement) to thrust-fault allochthons. Differential tilt between imbricate fault blocks suggests listric geometry at depth, whereas uniformly tilted blocks are more likely to be bounded by planar faults. The tilt direction of imbricate normal-fault blocks within large extensional allochthons is commonly away from the transport direction of these sheets, but in many cases tilts are in the same direction as transport, thus limiting the usefulness of the direction of tilting as a transport indicator. The presence of chaos structure, a structural style widely recognised in the Basin and Range Province, implies large scale simple shear on very low-angle normal faults and does not necessarily form as a result of listric faulting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47261, title ="Low-angle normal faults in the Basin and Range Province: nappe tectonics in an extending orogen", author = "Wernicke, Brian", journal = "Nature", volume = "291", number = "5817", pages = "645-648", month = "June", year = "1981", doi = "10.1038/291645a0", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140716-103854401", note = "© 1981 Macmillan Journals Ltd.\n\nReceived 18 December 1980; accepted 17 March 1981.\n\nI thank colleagues at MIT for discussions. This work was\nsupported by NSF grant EAR 7713637 awarded to B. C.\nBurchfiel.", revision_no = "12", abstract = "Cenozoic normal fault mosaics bounded beneath by a basal fault in the Basin and Range Province (BRP) have traditionally been described either in terms of large-scale surficial gravity sliding or by some form of in situ lower plate accommodation. I suggest here that these areas may be an extensional analogue to thin-skinned compressional orogens, a process which may even dominate active BRP tectonics.", }