[ { "id": "authors:w1a2x-jt884", "collection": "authors", "collection_id": "w1a2x-jt884", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150204-124834957", "type": "book_section", "title": "Jurassic rocks in Sonora, Mexico: Relations to the Mojave-Sonora megashear and its inferred northwestward extension", "book_title": "The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alternatives", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Rodr\u00edguez-Casta\u00f1eda", "given_name": "Jos\u00e9 Luis", "clpid": "Rodr\u00edguez-Casta\u00f1eda-J-L" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" } ], "abstract": "The Mojave-Sonora megashear constitutes a regional boundary between lithologically distinct Jurassic assemblages of different ages. North of the Mojave-Sonora megashear, arc-related volcanic, volcaniclastic, and clastic rocks, intruded by plutons (175\u2013160 Ma) compose part of the Middle Jurassic (commonly ca. 175 Ma) igneous province, previously recognized in Arizona and California. Distinct domains among Jurassic igneous rocks in northern Sonora are: (1) southern Papago, a region where pre-Jurassic rocks are unknown, (2) Nogales-Cananea-Nacozari, where Jurassic rocks are underlain by 1.7\u20131.4 Ga crystalline basement, and (3) Mojave-Sonora, where strata, including Oxfordian beds, along the north side of the Mojave-Sonora megashear are commonly strongly deformed, as recorded by thrust faults, mylonitic foliation, and recumbent folds. The Mojave-Sonora domain extends across the southwestern margins of the southern Papago and the Nogales-Cananea-Nacozari domains. Strong deformation that distinguishes the zone markedly declines within a few tens of kilometers northward. South of the Mojave-Sonora megashear, in central and southern Sonora, Lower Jurassic clastic and volcaniclastic rocks distinguish the Caborca domain. Upper Jurassic sedimentary rocks, commonly conglomeratic, are abundant north of Mojave-Sonora megashear; a single occurrence is known south of the Mojave-Sonora megashear. \n\nWaning of subduction-related Middle Jurassic magmatism was followed by the abrupt formation, ca. 165 Ma, of Coast Range, Josephine, Great Valley, and Devil's Elbow ophiolites and the Smartville Complex within oceanic pull-aparts west of the margin of the North America plate. The formation of ophiolitic rocks signaled the beginning of transtensional faulting. \n\nAlmost contemporaneously (ca. 163 Ma) the lowest volcanic units and overlying coarse sedimentary beds began to accumulate in fault-bounded continental pull-apart basins such as the McCoy Mountains basin. Other transtensional basins, formed at releasing steps where pull-aparts formed, are well developed within the Papago domain and other parts of southwestern United States and northern Mexico. \n\nFrom Sonora northward into California the Mojave-Sonora megashear fault zone, developed generally within the Middle Jurassic arc-parallel to the former continental margin, is inferred to link with strands of the Melones and Bear Mountain faults of the Foothills fault system, the Wolf Creek fault, and the Big Bend fault. A protuberance of Proterozoic basement (the Caborca block) that was truncated from the continental margin records \u223c800\u20131000 km of left-lateral offset. The displacement of the Caborca block took place south of a major releasing step along the Big Bend fault with the result that a regional pull-apart that coincides with the Great Valley of California developed. \n\nInboard of the Mojave-Sonora megashear Late Jurassic magmatic rocks crop out near faults at some releasing steps and within floors of some pull-apart structures. The distribution suggests that magma rose along faults and into areas of thin crust. In southern Arizona these igneous rocks are included as part of the Artesa layered sequence and the Ko Vaya plutonic suite. \n\nOxfordian and younger beds, which crop out north of the Mojave-Sonora megashear may contain exotic blocks and contractional structures that are contemporaneous with the Nevadan orogeny. The variation in the style and intensity of deformation of Middle and Upper Jurassic strata, and Upper Jurassic conglomerate rich in clasts derived from rocks of the Caborca domain, are postulated to record transpression near the Mojave-Sonora megashear that locally overlapped the more widespread transtensional structures in time and space. \n\nThe cessation of strike-slip faulting locally began ca. 150 Ma, as shown by undeformed intrusive bodies that cut older deformed Middle Jurassic rocks. By the time that the Independence dikes and correlative rocks were emplaced at 148 Ma, scant evidence of lateral faulting is known. \n\nIntrusions, young volcanic cover, transecting strike-slip faults, and multiple generations of low-angle extensional and contractional faults obscure Jurassic structures in Sonora and southern California. Despite these complications, removal of the effects of superposed structures reveals a viable trace for an inferred Late Jurassic left-lateral fault linking the Mojave-Sonora megashear and more northerly fault segments. The position of this major inferred fault is constrained by distinctive tectonostratigraphic domains. \n\nThe Middle and Late Jurassic and earliest Cretaceous plate tectonic history includes (1) subduction (175\u2013165 Ma), (2) coupling (ca. 165 Ma), (3) rifting, transtension, lateral faulting, transpression, and contraction (165\u2013145 Ma), and (4) renewed subduction (ca. 135 Ma) along the western margin of the North America plate and terranes (e.g., Wrangellia) to the west. The structures that record the diverse plate processes and that are preserved best in the overriding North America plate are compatible with a consistently maintained easterly directed maximum compressive stress.", "doi": "10.1130/0-8137-2393-0.51", "isbn": "9780813723938", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "2005", "pages": "51-95" }, { "id": "authors:319dr-mh610", "collection": "authors", "collection_id": "319dr-mh610", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150204-135028772", "type": "book_section", "title": "The Mojave-Sonora megashear \u2014 Field and analytical studies leading to the conception and evolution of the hypothesis", "book_title": "The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alternatives", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" } ], "abstract": "The megashear hypothesis is based upon reconnaissance geologic and geochronologic studies conducted principally from 1968 until 1974 in northwestern Sonora, Mexico. Our research incorporated U-Pb isotopic analyses of more than 70 zircon populations separated from 33 Precambrian rock samples with field relations and maps based upon structural and stratigraphic measurements. The results delineate a region known as the Caborca block and further reveal that the block is a principal element of an unexpected, discordant pattern of Proterozoic basement provinces. The Mojave-Sonora megashear was conceived in an effort to explain: (1) the unexpected pattern of two Proterozoic crystalline provinces with distinct chronologic histories of crust formation (1.8\u20131.7 Ga, Caborca block versus 1.7\u20131.6 Ga, Pinal Province); (2) the distribution of contrasting cover rocks overlying these basement blocks, (3) the abrupt northeastern limit of the Caborca block (terrane) against which volcanic and plutonic rocks of mid-Jurassic (mainly 180\u2013160 Ma) age are juxtaposed, and (4) the distribution of Jurassic magmatic units that intervene between the provinces of Proterozoic crust. The similarities that exist between crystalline crust and overlying pre-Jurassic cover in northwestern Sonora, Mexico, and units in the Inyo Mountains\u2013Death Valley region are attributed to the offset of correlative units along a Late Jurassic left-lateral strike-slip fault postulated to extend from the Gulf of Mexico to California and beyond. This large fault or megashear is a principal structure that accommodated 800\u20131000 km of left-lateral displacement among a set of transforms related to the opening of the Gulf of Mexico. The fault is compatible with Late Jurassic plate motion.\n\nThe inferred trace of the Mojave-Sonora megashear is obscured by contractional and extensional deformation and extensive plutonism. These processes, concentrated along the fault, commonly obfuscate and displace fault zone rocks along the inferred trace as well as the rocks adjacent to it. However, the fault zone is exposed in Sierra de Los Tanques near the international boundary between Mexico and the United States, where mylonitic rocks that comprise three aligned, discontinuous, segments crop out 1 for \u223c25 km. The zone of mylonitic rocks, which crosses Route 8, 13 km SW of Sonoita, is locally almost 5 km wide and separates Triassic granitoids and Precambrian gneiss from Jurassic volcanic and clastic rocks.\n\nThe limited exposure of the fault zone is a principal concern of those who object to the Mojave-Sonora megashear hypothesis. Studies of paleomagnetism, structure, stratigraphy, crustal geochemistry, and detrital zircons do not refute the megashear concept; commonly they reinforce existing evidence in support of the hypothesis.", "doi": "10.1130/0-8137-2393-0.1", "isbn": "9780813723938", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "2005", "pages": "1-50" }, { "id": "authors:fmssx-ckk31", "collection": "authors", "collection_id": "fmssx-ckk31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150206-123717397", "type": "book_section", "title": "Geology and geochronology of granitic batholith complex, Sinaloa, M\u00e9xico: Implications for Cordilleran magmatism and tectonics", "book_title": "Tectonic evolution of northwestern M\u00e9xico and the Southwestern USA", "author": [ { "family_name": "Henry", "given_name": "Christopher D.", "clpid": "Henry-C-D" }, { "family_name": "McDowell", "given_name": "Fred W.", "clpid": "McDowell-F-W" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Johnson", "given_name": "Scott E.", "clpid": "Johnson-S-E" } ], "abstract": "Most of southern Sinaloa is underlain by a large, composite batholith, a continuation\nof the better-known Cordilleran batholiths of California and Baja California. Field\nrelations and extensive K-Ar and U-Pb dating within a 120-km-wide and 120-km-deep\ntransect show that the Sinaloa batholith formed in several stages. Early layered gabbros\nhave hornblende K-Ar ages of 139 and 134 Ma, although whether these record\nemplacement age, cooling from metamorphism, or excess Ar is unresolved. A group of\nrelatively mafic tonalites and granodiorites were emplaced before or during an episode\nof deformation and are restricted to within 50 km of the coast. These plutons, referred\nto here as syntectonic, show dynamic recrystallization textures that suggest deformation\nbetween 300\u00b0 and 450 \u00b0C. A U-Pb zircon date on a probable syntectonic intrusion\nis 101 Ma. Hornblende K-Ar ages on definite syntectonic intrusions range between 98\nand 90 Ma; these may record cooling soon after emplacement or following regional\nmetamorphism.\nNumerous posttectonic intrusions crop out from within ~20 km of the coast, where\nthey intrude syntectonic rocks, to the eastern edge of the Sierra Madre Occidental,\nwhere they are covered by middle Cenozoic ash-flow tuffs. Posttectonic rocks are dominantly\nmore leucocratic granodiorites and granites. Three samples were analyzed by\nboth U-Pb and K-Ar methods. Their biotite and hornblende ages are concordant at 64,\n46, and 19 Ma and agree within analytical uncertainties with U-Pb zircon ages of 66.8,\n47.8, and 20 Ma. These data and field relations demonstrate that posttectonic intrusions\nwere emplaced at shallow depths and cooled rapidly. Therefore, concordant K-Ar age\npairs and hornblende ages in discordant samples approximate the time of emplacement.\nDiscordance of biotite-hornblende age pairs is largely if not entirely a result of reheating\nby younger plutons. The combined age data indicate that posttectonic intrusions were\nemplaced nearly continuously between 90 and 45 Ma. One intrusion is 20 Ma. Based on\noutcrop area, volumes of intrusions were relatively constant through time.\nThe combined geochronological data indicate that posttectonic magmatism\nshifted eastward between 1 and 1.5 km/Ma. Whether syntectonic magmatism also migrated is uncertain. Ages of middle and late Tertiary volcanic rocks indicate that\nmagmatism shifted rapidly (10-15 km/Ma) westward from the Sierra Madre Occidental\nafter ca. 30 Ma.\nThe Sinaloa batholith is borderline calc-alkalic to calcic. SiO_2 contents of analyzed\nrocks range from 47 to 74%; the lower limit excluding two gabbros is 54%. Syntectonic\nrocks are more mafic on average than posttectonic rocks. SiO_2 contents of seven out of\nnine analyzed syntectonic rocks range narrowly between 59 and 62%, with one each at\n65 and 67%. The posttectonic rocks show a wider range from 54 to 74% SiO_2, but only\nborder phases and small intrusions have SiO_2 less than ~63%. Combined with their\ndistribution, these data indicate that intrusions become more silicic eastward. The fact\nthat the 20 Ma intrusion is relatively mafic (61 % SiO_2\n) and lies near the coast with syntectonic\nrocks indicates that composition is related to location rather than to age.\nThe Sinaloa batholith shows both marked similarities and differences from\nbatholiths of the Peninsular Ranges, Sonora, Caho San Lucas (Baja California Sur),\nand Jalisco. The greatest similarities are in types of intrusions, a common sequence\nfrom early gabbro through syntectonic to posttectonic rocks, and general eastward\nmigration of magmatism. However, the end of deformation recorded by syntectonic\nrocks may be different in each area. Sinaloa rocks show a similar wide range of compositions\nas rocks of the Peninsular Ranges and Sonora but are more potassic than\nthe calcic Peninsular Ranges. Rare earth element patterns are most like those of the\neastern part of the Peninsular Ranges and central part of Sonora, both areas that\nare underlain by Proterozoic crust or crust with a substantial Proterozoic detrital\ncomponent. However, southern Sinaloa lies within the Guerrero terrane, which is\ninterpreted to be underlain by accreted Mesozoic crust. The greatest differences are\nin distance and rate of eastward migration. Published data show that magmatism\nmigrated eastward at ~10 km/Ma across the Peninsular Ranges and Sonora and from\nJalisco southeast along the southwestern M\u00e9xico coast. The area of slower eastward\nmigration roughly correlates with the location of the Guerrero terrane and of possibly\naccreted oceanic crust that is no older than Jurassic.", "doi": "10.1130/0-8137-2374-4.237", "isbn": "9780813723747", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "2003", "pages": "237-273" }, { "id": "authors:8gfm2-tmb17", "collection": "authors", "collection_id": "8gfm2-tmb17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150225-125536778", "type": "book_section", "title": "Jurassic volcanic rocks in northeastern Mexico: A possible remnant of a Cordilleran magmatic arc", "book_title": "Studies on the Mesozoic of Sonora and adjacent areas", "author": [ { "family_name": "Jones", "given_name": "Norris W.", "clpid": "Jones-N-W" }, { "family_name": "McKee", "given_name": "James W.", "clpid": "McKee-J-W" }, { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Jacques-Ayala", "given_name": "C\u00e9sar", "clpid": "Jacques-Ayala-C" }, { "family_name": "Gonz\u00e1lez-L\u00e9on", "given_name": "Carlos M.", "clpid": "Gonz\u00e1lez-L\u00e9on-C-M" }, { "family_name": "Rold\u00e1n-Quintana", "given_name": "J.", "clpid": "Rold\u00e1n-Quintana-J" } ], "abstract": "Pre-Oxfordian Mesozoic subaerial volcanogenic rocks occur in a band extending\nnorthwest from Ciudad Victoria, Tamaulipas, to Santa Maria del Oro, Durango.\nThese strata include Nazas, Rodeo, and Caopas Formations in Durango, Coahuila,\nand Zacatecas; La Boca Formation and its underlying volcanic basement at Canon\nde Huizachal, Tamaulipas; and volcanic units below La Joya Formation at Real de\nCatorce and Charcas, San Luis Potosi. Rocks at these localities have similar lithologies,\nstratigraphic positions, and paleontologic and isotopic ages. Field mapping in\nthe Caopas-Pico de Teyra area, northern Zacatecas, and ancillary research provide\ninsight into the nature of this suite.\nAt least 3 km of abundant airfall tuff, tuffaceous siltstone, and uncommon ashflow\ntuff are present near Pico de Teyra; this sequence appears to belong to a more\ndistal facies than the flows, breccias, and laharic conglomerates of the Nazas and\nRodeo Formations exposed 25 km to the north. Porphyritic rhyolite (Caopas Formation)\noccurs within these volcanogenic rocks as a fault-bounded block and is interpreted\nas a cogenetic, subvolcanic pluton. A relatively undeformed portion of the\nCaopas has yielded a zircon U-Pb age of 158 \u00b1 4 Ma. Petrographic and limited chemical\ndata from these formations show that calc-alkaline andesite, dacite, and rhyolite\nare the most common compositions.\nThe volcanogenic rocks in northeastern Mexico are south of the inferred trace of\nthe Mojave-Sonora megashear. Their large volume, their lithologic and chemical characteristics,\nand their age suggest that these rocks may be a component of the Jurassic\narc of western North America that was translated southeastward along the megashear.", "doi": "10.1130/0-8137-2301-9.179", "isbn": "9780813723013", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1995", "pages": "179-190" }, { "id": "authors:mpsek-gay33", "collection": "authors", "collection_id": "mpsek-gay33", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180717-105639238", "type": "book_section", "title": "Transcontinental Proterozoic provinces", "book_title": "Precambrian: Conterminous U.S.", "author": [ { "family_name": "Anderson", "given_name": "J. Lawford", "clpid": "Anderson-J-L" }, { "family_name": "Bender", "given_name": "E. Erik", "clpid": "Bender-E-E" }, { "family_name": "Anderson", "given_name": "Raymond R.", "clpid": "Anderson-R-R" }, { "family_name": "Bauer", "given_name": "Paul W.", "clpid": "Bauer-P-W" }, { "family_name": "Robertson", "given_name": "James M.", "clpid": "Robertson-J-M" }, { "family_name": "Bowring", "given_name": "Samuel A.", "clpid": "Bowring-S-A" }, { "family_name": "Condie", "given_name": "Kent C.", "clpid": "Condie-K-C" }, { "family_name": "Denison", "given_name": "Rodger E.", "clpid": "Denison-R-E" }, { "family_name": "Gilbert", "given_name": "M. Charles", "clpid": "Gilbert-M-C" }, { "family_name": "Grambling", "given_name": "Jeffrey A.", "clpid": "Grambling-J-A" }, { "family_name": "Mawer", "given_name": "Christopher K.", "clpid": "Mawer-C-K" }, { "family_name": "Shearer", "given_name": "C. K.", "clpid": "Shearer-C-K" }, { "family_name": "Hinze", "given_name": "William J.", "clpid": "Hinze-W-J" }, { "family_name": "Karlstrom", "given_name": "Karl E.", "clpid": "Karlstrom-K-E" }, { "family_name": "Kisvarsanyi", "given_name": "E. B.", "clpid": "Kisvarsanyi-E-B" }, { "family_name": "Lidiak", "given_name": "Edward G.", "clpid": "Lidiak-E-G" }, { "family_name": "Reed", "given_name": "John C., Jr.", "clpid": "Reed-J-C-Jr" }, { "family_name": "Sims", "given_name": "Paul K.", "clpid": "Sims-P-K" }, { "family_name": "Tweto", "given_name": "Odgen", "clpid": "Tweto-O" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Treves", "given_name": "Samuel B.", "clpid": "Treves-S-B" }, { "family_name": "Williams", "given_name": "Michael L.", "clpid": "Williams-M-L" }, { "family_name": "Wooden", "given_name": "Joseph L.", "clpid": "Wooden-J-L" } ], "contributor": [ { "family_name": "Reed", "given_name": "John C., Jr.", "clpid": "Reed-John-C-Jr" }, { "family_name": "Bickford", "given_name": "Marion E.", "clpid": "Bickford-Marion-E" }, { "family_name": "Houston", "given_name": "R. S.", "clpid": "Houston-R-S" }, { "family_name": "Link", "given_name": "Paul Karl", "clpid": "Link-Paul-Karl" }, { "family_name": "Rankin", "given_name": "D. W.", "clpid": "Rankin-D-W" }, { "family_name": "Sims", "given_name": "Paul K.", "clpid": "Sims-Paul-K" }, { "family_name": "Van Schmus", "given_name": "W. Randall", "clpid": "Van-Schmus-W-Randall" } ], "abstract": "Research on the Precambrian basement of North America over the past two decades has shown that Archean and earliest Proterozoic evolution culminated in suturing of Archean cratonic elements and pre-1.80-Ga Proterozoic terranes to form the Canadian Shield at about 1.80 Ga (Hoffman, 1988,1989a, b). We will refer to this part of Laurentia as the Hudsonian craton (Fig. 1) because it was fused together about 1.80 to 1.85 Ga during the Trans-Hudson and Penokean orogenies (Hoffman, 1988). The Hudsonian craton, including its extensions into the United States (Chapters 2 and 3, this volume), formed the foreland against which 1.8- to 1.6-Ga continental growth occurred, forming the larger Laurentia (Hoffman, 1989a, b). Geologic and geochronologic studies over the past three decades have shown that most of the Precambrian in the United States south of the Hudsonian craton and west of the Grenville province (Chapter 5) consists of a broad northeast to east-northeast-trending zone of orogenic provinces that formed between 1.8 and 1.6 Ga. This zone, including extensions into eastern Canada, comprises or hosts most rock units of this age in North America as well as extensive suites of 1.35- to 1.50-Ga granite and rhyolite. This addition to the Hudsonian Craton is referred to in this chapter as the Transcontinental Proterozoic provinces (Fig. 1); the plural form is used to denote the composite nature of this broad region. \n\nThe Transcontinental Proterozoic provinces consist of many distinct lithotectonic entities that can be defined on the basis of regional lithology, regional structure, U-Pb ages from zircons, Sr-Nd-Pb isotopic signatures, and regional geophysical anomalies.", "doi": "10.1130/DNAG-GNA-C2.171", "isbn": "9780813752181", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1993-01-01", "pages": "171-334" }, { "id": "authors:thg54-ejy65", "collection": "authors", "collection_id": "thg54-ejy65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141111-080640739", "type": "book_section", "title": "Non-SAF type focal mechanisms adjacent to the SAF, Mojave Segment: Implications for Blind Thrust Beneath the San Gabriel Mountains, Southern California", "author": [ { "family_name": "Huang", "given_name": "Weishi", "clpid": "Huang-Weishi" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "contributor": [ { "family_name": "Chen", "given_name": "Zhangli", "clpid": "Chen-Zhangli" } ], "abstract": "Focal mechanisms of earthquakes with 2.5 \u2264 M \u2264 4.1 from 1978 to 1990 were analyzed within\na 15 km-wide belt of the San Andreas fault (SAF) zone, in the Mojave segment, southern\nCalifornia. Of the 29 events, 41% are strike-slip, 28% oblique--slip, 24% thrust, and 7% are normal\nfault types. Most of the thrust events are located in the central section of the studied zone,\nwhere the fault geometry is relatively simple. In contrast, most of the strike-slip events arc at the\nintersection between the SAF and the San Jacinto fault. Both stress tensor inverted from slip\nvectors and strain tensor calculated from earthquake moment tensors produce similar directions of\nmaximum principal compressional axes that arc oriented in the direction between 351\u00b0 and 5\u00b0,\nwhich is at an angle of about 60\u00b0 to the strike of the SAF. These non-SAF type faulting events obviously\ncan not be explained by simple shear motion on the SAF. Instead, they accrued on the\nstructures that were activated in response to the regional N compression at the latitude of the\nTransverse Ranges. For the thrust events, we interpret that a back thrust (northward thrust) exists\nbeneath the northern side of the San Gabriel Mountains. This back thrust is located at the depth of\n8-13 km, within or beneath the Pelona schist. It is apparently associated with aseismic slip and uplifts\nthe San Gabriel Mountains on the northern side.", "publisher": "Beijing Seismological Press", "publication_date": "1993" }, { "id": "authors:5gz0g-nj322", "collection": "authors", "collection_id": "5gz0g-nj322", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220728-175419049", "type": "book_section", "title": "Daughter-parent isotope systematics in U-Th-bearing igneous accessory mineral aseemblages as potential indices of metamorphic history: A discussion of the concept", "book_title": "Stable isotope geochemistry : a tribute to Samuel Epstein", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Taylor", "given_name": "Hugh P., Jr.", "clpid": "Taylor-H-P-Jr" }, { "family_name": "O'Neil", "given_name": "James R.", "clpid": "O'Neil-James-R" }, { "family_name": "Kaplan", "given_name": "Isaac R.", "clpid": "Kaplan-Isaac-R" } ], "abstract": "It is proposed that the patterns of isotopic disturbance in Pb-U-Th systems for the assemblage of radioactive minerals in any granite or equivalent orthogneiss may have value not only as geochronological tools for determining the time constants of metamorphic events but also may have significant potential as indices of the nature and intensity of metamorphism (including thermal, hydrothermal, deformational, weathering, and other environments of change). One of the special qualities of radiogenic Pb-U-Th geochemistry is the coexistence of three daughter-parent (D/P) systems: \u00b2\u2070\u2076Pb/\u00b2\u00b3\u2078U, \u00b2\u2070\u2077Pb/\u00b2\u00b3\u2075U, and \u00b2\u2070\u2078Pb/\u00b2\u00b3\u00b2Th. The uranogenic pair of D/P systems are coupled chemically so that they lead to rigorously linked isotope ratio variations during disturbance. The thorogenic D/P system, because of the contrasting Th and U chemistry, may behave quite independently, providing special insights into the mobility of Pb, U, and Th. \n\nAccessory mineral assemblages in most rocks contain from three to eight or more radioactive minerals in which U and Th commonly are quite fractionated. Each mineral and its three contained D/P systems appear to have distinctive responses to metamorphism and show differential sensitivity to different metamorphic variables. The responses are conditioned by accumulated radiation damage at the time of metamorphism. Each mineral species has a unique structural response to influence, and commonly shows large inter- and intra-grain variations in accumulated disorder. The rate-competitive roles of structural annealing and metamorphic disturbance are believed to determine the net effect on the D/P systems. \n\nAny individual sample may be treated as an isogradic collection of responses at a given position in a metamorphic gradient. The number of minerals X 3 D/P systems provides a large matrix of sensitive, precisely measured parameters for characterizing that position in the gradient. Several properly selected samples can characterize the entire gradient. This then offers a general basis for extracting quantitative indices of the nature and intensity of the metamorphism. Ultimately, this may permit calibration of metamorphic effects derived from several important variables neglected in some current thermochronological models. Hypothetical models representing possible assemblage D/P responses derived from different metamorphic disturbances are offered. Some examples from southern California of natural responses to metamorphism are provided: (1) The effects of mylonitization as a modifier of the radioactive mineral assemblages are clearly demonstrated in titanite, apatite, and allanite in a tonalite pluton cut by the Eastern Peninsular Ranges mylonite zone. (2) The correlation of radiation damage with isotopic disturbance in zircons is documented in a Cretaceous granodiorite that was hydrothermally altered during the Miocene.", "isbn": "0-941809-02-1", "publisher": "Geochemical Society", "place_of_publication": "San Antonio, TX", "publication_date": "1991", "pages": "391-407" }, { "id": "authors:kzhej-k3t78", "collection": "authors", "collection_id": "kzhej-k3t78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-110611222", "type": "book_section", "title": "Geochemical modeling of a steeply dipping boundary between continental and oceanic-arc lithosphere, west-central Idaho", "author": [ { "family_name": "Manduca", "given_name": "Cathryn A.", "clpid": "Manduca-C-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P-Jr" } ], "abstract": "The western margin of the Cretaceous Idaho Batholith intruded the boundary between accreted oceanic and terranes and the continental margin. The geochemistry of the plutonic rocks indicates that it is an abrupt, steeply dipping boundary which\nextends through the lithosphere.", "publisher": "Geochemical Society", "publication_date": "1990-05" }, { "id": "authors:kpyfq-tyf31", "collection": "authors", "collection_id": "kpyfq-tyf31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-162428094", "type": "book_section", "title": "Tectonic and magmatic contrasts across a two-province Proterozoic boundary in central Arizona", "author": [ { "family_name": "Conway", "given_name": "Clay M.", "clpid": "Conway-Clay-M" }, { "family_name": "Karlstrom", "given_name": "Karl E.", "clpid": "Karlstrom-Karl-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Wrucke", "given_name": "Chester T.", "clpid": "Wrucke-Chester-T" } ], "contributor": [ { "family_name": "Davis", "given_name": "George H.", "clpid": "Davis-George-H" }, { "family_name": "VandenDolder", "given_name": "Evelyn M.", "clpid": "VandenDolder-Evelyn-M" } ], "abstract": "One of the first major discoveries of the infant discipline of zircon geochronology was that the Early Proterozoic of Arizona comprised two age provinces with a boundary in the central part of the state (Silver, 1965, 1967, 1969). Rocks in the central to northwestern part of the state are about 1.70 to 1.78 Ga, whereas those in the central to southeastern part of the state are about 1.61 to 1.71 Ga. Since these results were first reported, the exact position and nature of the two-province boundary have been the subject of much debate and still elude geologists. It has become obvious that several iterations of field and geochronologic studies, each giving direction and raising questions for the next, are required for a understanding of the boundary and the Early Proterozoic history of Arizona in any detail. Because The two-province boundary in Arizona may extend northeastward into the mid-continent and perhaps farther and because the Transition Zone in Arizona offers superb outcrops across this boundary, Arizona may hold answers to questions regarding the Early Proterozoic crustal growth of the southern part of the North American craton. One of the major goals of this field trip is to examine the nature of the proposed boundary through stops and discussions of rocks in both provinces.", "publisher": "University of Arizona", "publication_date": "1987-10" }, { "id": "authors:9jjj3-8m872", "collection": "authors", "collection_id": "9jjj3-8m872", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-154917734", "type": "book_section", "title": "A note on the magnitude of possible uranium losses from granites of the conterminous United States", "book_title": "Proceedings of the Symposium on Uranium Exploration Methods: review of the NEA/IAEA R & D Programme", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Two independent calculations suggest that, on average, about 20 - 25 percent of the primary uranium endowment of granites in the conterminous United States may have been lost. The methods of calculation and the data which they employ need refinement, but the implications for modelling radioactive granites as sources for uranium are significant.", "isbn": "978-92-64-02350-5", "publisher": "Nuclear Energy Agency, Organisation for Economic Co-operation and Development", "place_of_publication": "Paris, France", "publication_date": "1982-06", "pages": "457-462" }, { "id": "authors:q21tm-y7v29", "collection": "authors", "collection_id": "q21tm-y7v29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-151508769", "type": "book_section", "title": "Primary mineral distribution and secondary mobilization of uranium and thorium in radioactive granites", "book_title": "Proceedings of the Symposium on Uranium Exploration Methods: review of the NEA/IAEA R & D Programme", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Woodhead", "given_name": "James A.", "clpid": "Woodhead-James-A" }, { "family_name": "Williams", "given_name": "Ian S.", "clpid": "Williams-Ian-S" } ], "abstract": "Radioactive granites in the southwestern United States tend to form distinct geochemical provinces, for which the resistant mineral zircon provides useful indices of primary igneous endowments. A large fraction of the uranium and thorium in these granites is contained in trace minerals, stoichiometric for the actinides (e.g. brannerite, coffinite, uranothorite), present at levels up to tens of ppm. Secondary mobilization of uranium in radioactive rocks seems most dependent on the geochemical stability of these rare phases, especially after their modification by radiation damage. U-Th-Pb isotope systematics provide several independent indications of the magnitude and timing of uranium transfers (1) within the granitic systems in what we believe are important preparation processes, and (2) to sites outside the granites including potential secondary uranium ore deposits.", "isbn": "978-92-64-02350-5", "publisher": "Nuclear Energy Agency, Organisation for Economic Co-operation and Development", "place_of_publication": "Paris, France", "publication_date": "1982-06", "pages": "355-367" }, { "id": "authors:df0vg-pe914", "collection": "authors", "collection_id": "df0vg-pe914", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-170434698", "type": "book_section", "title": "\u2078\u2077Sr/\u2078\u2076Sr and \u00b9\u2078O/\u00b9\u2076O variations within a single intrusive unit of the Peninsular Ranges batholith, San Jacinto mountains, southern California", "author": [ { "family_name": "Hill", "given_name": "R. I.", "clpid": "Hill-R-I" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "H. P., Jr.", "clpid": "Taylor-H-P-Jr" } ], "contributor": [ { "family_name": "Kagakukai", "given_name": "Nihon Chikyu", "clpid": "Kagakukai-Nihon-Chikyu" } ], "abstract": "The Peninsular Ranges batholith (PRB) of southern California and Baja California shows striking transverse asymmetries in many geochemical parameters (e.g. Early and Silver, 1973; Taylor and Silver, 1978; Silver et. al., 1979). Initial \u2078\u2077Sr/\u2078\u2076Sr (Sr_i) generally becomes more radiogenic (0.703-0.708) and \u03b4\u00b9\u2078o increases (6.0 to 12.8) from west to east (continentward), except in the San Jacinto - Santa Rosa Mtns block at the extreme northeast. Taylor and Silver (1978) suggested this anomalous region may be attributable to local involvement of the southwest edge of North American cratonic crystalline basement in the fusion process that produced these magmas.", "publisher": "Geological Survey of Japan", "publication_date": "1982-04" }, { "id": "authors:rrgwd-rw768", "collection": "authors", "collection_id": "rrgwd-rw768", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180725-085833699", "type": "book_section", "title": "Precambrian of the Conterminous United States", "book_title": "Perspectives in Regional Geological Synthesis: Planning for the Geology of North America", "author": [ { "family_name": "Reed", "given_name": "John C., Jr.", "clpid": "Reed-J-C-Jr" }, { "family_name": "Sims", "given_name": "Paul K.", "clpid": "Sims-P-K" }, { "family_name": "Houston", "given_name": "Robert S.", "clpid": "Houston-R-S" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Rankin", "given_name": "Douglas W.", "clpid": "Rankin-D-W" }, { "family_name": "Reynolds", "given_name": "Mitchell W.", "clpid": "Reynolds-M-W" } ], "contributor": [ { "family_name": "Palmer", "given_name": "A. R.", "clpid": "Palmer-A-R" } ], "abstract": "Precambrian rocks are at or near the surface in only about 10 percent of the conterminous United States, but it can reasonably be inferred that they comprise the continetal crust beneath about 90 percent. They are missing or unrecognized in the exotic terranes along the Pacific margin of North America, but they probably form significant parts of the crust in exotic terranes or continental fragments accreted to the eastern part of the continent during Paleozoic time. Thus, the total area of Precambrian rocks to be considered in this volume is comparable to that of the exposed Precambrian of the Canadian Shield. It is important to remember that in spite of the enormous lateral extent of the craton the volume of the continental crust is almost insignificant. The width of the North American craton is more than half the radius of the planet, but the thickness of the continental crust is less than one hundredth of the planetary radius (fig. 1). The volume of the crust is less than 2 percent of the volume of the mantle beneath the U.S. part of North America.\n\nPrecambrian rocks contain the only available record of the assembly and evolution of the fragile continental raft that we know as North America during more than four fifths of geologic time. Of the areas of exposed Precambrian rocks in the conterminous United States, about half have been covered by modern reconnaissance geologic mapping (scale 1:250,000 or larger); less than a quarter have been covered by detailed modern mapping (scale 1:62,500 or larger).", "doi": "10.1130/DNAG-SPEC-v1.7", "isbn": "9780813752013", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1982-01-01", "pages": "7-14" }, { "id": "authors:8ncyj-k8373", "collection": "authors", "collection_id": "8ncyj-k8373", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-413253000", "type": "book_section", "title": "Distribution and U-Pb isotope ages of some lineated plutons, northwestern Mexico", "book_title": "Cordilleran Metamorphic Core Complexes", "author": [ { "family_name": "Anderson", "given_name": "T. H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Salas", "given_name": "G. A.", "clpid": "Salas-G-A" } ], "contributor": [ { "family_name": "Crittenden", "given_name": "Max D., Jr.", "clpid": "Crittenden-Max-D-Jr" }, { "family_name": "Coney", "given_name": "Peter J.", "clpid": "Coney-Peter-J" }, { "family_name": "Davis", "given_name": "George H.", "clpid": "Davis-George-H" } ], "abstract": "Characteristically lineated and foliated rocks of middle to late Mesozoic(?) age crop out in ranges in north-central Sonora throughout an area of 15,000 km2, between lat 31\u00b0 307\u2032N and 30\u00b0 30\u2032N. The terrane consists predominantly of layered sedimentary, volcanic, and volcaniclastic units, commonly metamorphosed to greenschist facies. Associated plutons, which are unambiguously intrusive, consist mainly of biotite- or biotite-muscovite\u2013bearing granite. The layered suite and intrusive rocks are distinguished by subhorizontal, penetrative lineation, commonly defined by smeared mineral grains, which consistently trend northeast. Foliation is also predominantly low dipping. South of lat 30\u00b0 30\u2032N, sporadic occurrences of lineated granitic and metamorphic rocks suggest the existence of this deformational fabric at least to Sierra Mazatan, which lies east of Hermosillo near lat 29\u00b000\u2032N.\n\nCogenetic suites of zircon from one undeformed and three deformed plutons yield U-Pb ages from 75 to 55 m.y. These intrusive bodies are elements of a widespread, time-transgressive, late Mesozoic magmatic suite. They are not known to be affected by folds and faults commonly related to the Laramide orogeny. The apparent ages of the plutons are interpreted to be crystallization ages and therefore indicate that lineation and foliation formed, at least locally, later than 55 m.y. ago.\n\nOutcrops of distinctively deformed rocks appear to crudely define a north-trending belt. Rocks outside of this general zone are composed of sedimentary, volcanic, and volcaniclastic rocks of Precambrian and Mesozoic age which locally have been strongly folded and metamorphosed to greenschist or higher facies. However, postdeformational pegmatites and intrusive rocks indicate pre-Tertiary minimum ages for related episodes of deformation and metamorphism.", "doi": "10.1130/mem153-p269", "isbn": "9780813711539", "publisher": "Geological Society of America", "place_of_publication": "Boulder, CO", "publication_date": "1980-01", "pages": "269-283" }, { "id": "authors:7zk2d-jg766", "collection": "authors", "collection_id": "7zk2d-jg766", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221114-215136326", "type": "book_section", "title": "Problems of pre-Mesozoic continental evolution", "book_title": "Continental tectonics", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "By virtue of its remarkable ability to explain currently observed dynamic processes of ocean basins and continental margins, and to account for much of the geological record of the last 200 million years (m.y.), the plate-tectonics model is a rational starting point in interpreting the earlier evolutionary history of the earth. The model's numerous predictions facilitate continued testing and upgrading of its own validity. Since early Mesozoic time, modern continental margins have developed with distinctive physical and chemical characteristics that can serve as bases for comparative studies of older margins, which have been incorporated within the continents in the past. The recent progress of geological studies in North America and the diversity of its geological endowments make the United States a particularly appropriate region for many of these essential investigations.", "isbn": "978-0-309-02928-5", "publisher": "National Academy of Sciences", "place_of_publication": "Washington, D.C.", "publication_date": "1980", "pages": "26-29" }, { "id": "authors:hfr9g-tve61", "collection": "authors", "collection_id": "hfr9g-tve61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220801-222836655", "type": "book_section", "title": "Profile of rare earth element characteristics across the Peninsular Ranges Batholith near the international border, southern California, U.S.A., and Baja California, Mexico", "author": [ { "family_name": "Gromet", "given_name": "L. Peter", "clpid": "Gromet-L-Peter" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Abbott", "given_name": "Patrick L.", "clpid": "Abbott-Patrick-L" }, { "family_name": "Todd", "given_name": "Victoria R.", "clpid": "Todd-Victoria-R" } ], "abstract": "This brief report summarizes REE abundances and fractionations in a number of rocks in a profile across the Peninsular Ranges batholith, in the region east of San Diego, California, and Tijuana, B.C., Mexico. \n\nThe data are from part of a more extensive investigation of the REE geochemistry in the northern 600 km of the batholith. (Gromet and Silver, 1977; Gromet, 1979; Gromet and Silver, 1979, and in preparation). Other contributions in this guidebook report systematic variations in the geochemistry, petrology and history of the batholith, as revealed in transverse traverses. Consequently, emphasis is placed on examining the extent to which the well-defined REE geochemical characteristics can be related to other major characteristics of the batholithic complex.", "publisher": "San Diego State University", "publication_date": "1979-11" }, { "id": "authors:tsfbj-78z66", "collection": "authors", "collection_id": "tsfbj-78z66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-175848999", "type": "book_section", "title": "Some petrological, geochemical and geochronological observations of the Peninsular Ranges Batholith near the international border of the U.S.A. and Mexico", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P., Jr.", "clpid": "Taylor-H-P-Jr" }, { "family_name": "Chappell", "given_name": "Bruce", "clpid": "Chappell-Bruce" } ], "contributor": [ { "family_name": "Abbot", "given_name": "Patrick L.", "clpid": "Abbot-Patrick-L" }, { "family_name": "Todd", "given_name": "Victoria R.", "clpid": "Todd-Victoria-R" } ], "abstract": "The Peninsular Ranges batholith of southern California, U.S.A., and Baja California, Mexico, is a major segment of the great chain of late Mesozoic batholiths found on continental margins around the Pacific basin. The structural, petrological and geochemical character of this batholith seems to reflect the details of its particular tectonic setting on the southwestern margin of North America. The evolution of the batholith in time and space is inferred to have been controlled by the nature and rates of convergent interactions which occurred between the America plate to the east and unidentified oceanic plates to the west (possibly, but not necessarily, including the Kula and Farallon plates). A long episode of subduction with intermittent transform faulting in the Cenozoic has removed direct evidence for the age, relative motion and dimensions of these plates. The magmatic arc represented by the Peninsular Ranges batholith and its associated volcanic superstructure can provide much useful information about the nature of regional plate tectonics during the late Mesozoic. Field, petrological, geochemical and geochronological studies by a number of workers have revealed remarkable regularities in the architecture of the batholith which now provide significant constraints on interpretations of the plate interactions. More directly, these regularities provide valuable guides to the nature of the petrological processes and source regions from which the batholith was derived. In this article, observations made in a transverse 70 km strip of the batholith, 130 km long ENE, along the international border near San Diego, California, and Tijuana, Baja California (Figure 1) are organized to illustrate the nature of the transverse asymmetry of the batholith as it has been emerging from continuing field and laboratory studies. Although the data density for many parameters in this traverse region is less than optimal, the patterns are consistent with much larger bodies of observations from the entire northern 600 km of the batholith, except perhaps for the San Jacinto block, which exhibits some unique features. The latter terrane, which lies between the San Jacinto and San Andreas faults in the NE portion of the batholith, is therefore excluded from the following discussion.", "publisher": "San Diego State University", "publication_date": "1979-11" }, { "id": "authors:nw04d-k3133", "collection": "authors", "collection_id": "nw04d-k3133", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220720-154525923", "type": "book_section", "title": "Geologic analysis of ASTP photographs of parts of Southern California", "author": [ { "family_name": "Powell", "given_name": "R. E.", "clpid": "Powell-R-E" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "El-Baz", "given_name": "Farouk", "clpid": "El-Baz-Farouk" }, { "family_name": "Warner", "given_name": "Delia M.", "clpid": "Warner-Delia-M" } ], "abstract": "On July 16, 1975, the crew of the Apollo-Soyuz Test Project obtained a series of remarkably clear color stereoscopic photographs of the central Transverse Ranges and the Los Angeles Basin in southern California. These photographs are used to identify and interpret known geologic features of the Transverse Ranges, and to search for previously unrecognized features. High-altitude aerial photographs provide useful supplements to the orbital photographs. Major well-known high-angle faults of the region (the San Andreas, San Gabriel, and San Jacinto faults) are clearly visible; low-angle faults, even if active, are less apparent. The sharpness of the visual definition of a fault zone, therefore, should not be used as an exclusive criterion for recency of activity. Conversely, pronounced topographic expression may be developed by preferential erosion along inactive fault zones. Vegetation can produce severe masking of originally strong lithologic contrasts. Within and bounding the San Gabriel Mountains, current and recent fault breakage indicate a complex interplay of strike-slip and thrust fault movement. A previously unrecognized pattern of east-northeast-trending lineaments and the lobate character of the mountain front offer new perspectives to possible tectonic interpretations of this mountain range. They suggest the possibility that fault movement may represent a series of shingled slabs moving either in independent or in grouped increments, in response to compressive components across the Pacific/North America plate boundary.", "publisher": "National Aeronautics and Space Administration", "publication_date": "1979" }, { "id": "authors:yy21f-hz079", "collection": "authors", "collection_id": "yy21f-hz079", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220728-150030088", "type": "book_section", "title": "Precambrian Formations and Precambrian History in Cochise County, Southeastern Arizona", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Callender", "given_name": "J. F.", "clpid": "Callender-J-F" }, { "family_name": "Wilt", "given_name": "J. C.", "clpid": "Wilt-J-C" }, { "family_name": "Clemons", "given_name": "R. E.", "clpid": "Clemons-R-E" }, { "family_name": "James", "given_name": "H. L.", "clpid": "James-H-L" } ], "abstract": "Precambrian rocks of southeastern Arizona typically are\nexposed in isolated masses in a number of the tectonically\ncomplex ranges of the southern Basin and Range province.\nPreservation of original sedimentary and igneous textures and\nstructures is commonly excellent, but the combination of extended\nPrecambrian histories, discontinuous exposure and\nvariable overlay of Mesozoic and Cenozoic deformation, magmatism\nand metamorphism provides major challenges for\nregional Precambrian correlations and historical interpretations.\nFor all of the problems, however, the early work of F.\nL. Ransome (1903, 1904, 1915, 1919, 1923, and elsewhere)\nand N. L. Darton (1924, 1925) successfully established a basic\nPrecambrian stratigraphic framework for this region which\nsubsequent studies have refined but not replaced.", "publisher": "New Mexico Geological Society", "publication_date": "1978-11" }, { "id": "authors:e9yqh-mjz45", "collection": "authors", "collection_id": "e9yqh-mjz45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-154007495", "type": "book_section", "title": "Oxygen isotope relationships in plutonic igneous rocks of the Peninsular Ranges Batholith, southern and Baja California", "author": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P-Jr" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Zartman", "given_name": "R. E.", "clpid": "Zartman-R-E" } ], "abstract": "Whole-rock \u03b4\u00b9\u2078O values have been determined for 155 samples from approximately 140 plutons 1n the northern 600 km of the Peninsular Ranges batholith (fig. 1). Analyses of tonalites, granodiorites, gabbros and a few quartz monzonites are represented in crude proportion to the abundance of these rocks in the batholith. \n\nHost samples have been studied also for U-Pb zircon geochronology (Banks and Silver, 1968; Silver and others, 1968); K-Rb-Sr isotope and trace element systematics (Early and Silver, 1973); and rare earth element distributions (Gromet and Silver, 1977). All of these parameters display striking geographic regularities and profound transverse asymmetries related to the NNW-trending plutonic arc (Silver and others, 1975; Silver and Early, 1977).", "publisher": "U. S. Geological Survey", "publication_date": "1978-08" }, { "id": "authors:3psve-5yp18", "collection": "authors", "collection_id": "3psve-5yp18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220711-195641295", "type": "book_section", "title": "Nuclear Energy Resources", "book_title": "The Impact of the Geosciences on Critical Energy Resources", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Burk", "given_name": "Creighton A.", "clpid": "Burk-Creighton-A" }, { "family_name": "Drake", "given_name": "Charles L.", "clpid": "Drake-Charles-L" } ], "abstract": "The interactions of the geological sciences with nuclear\nenergy power development have been continuous since the first\nuranium fuel supplies were sought but they have recently intensified at an even faster pace than the growth of this remarkable energy source.", "isbn": "9780429047718", "publisher": "Routledge", "place_of_publication": "New York, NY", "publication_date": "1978-02-13", "pages": "69-84" }, { "id": "authors:h1jgr-pdc29", "collection": "authors", "collection_id": "h1jgr-pdc29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221018-200459160", "type": "book_section", "title": "Geological Features of Southwestern North America", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Anderson", "given_name": "T. H.", "clpid": "Anderson-T-H" }, { "family_name": "Conway", "given_name": "C. M.", "clpid": "Conway-C-M" }, { "family_name": "Murray", "given_name": "J. D.", "clpid": "Murray-J-D" }, { "family_name": "Powell", "given_name": "R. E.", "clpid": "Powell-R-E" } ], "abstract": "The SKYLAB 4 crewmen conducted visual observations of seven designated geological target areas and\nother targets of opportunity in parts of southwestern\nUnited States and northwestern Mexico. The experiments\nwere designed to determine how effectively\ngeologic features could be observed from orbit and what\nresearch information could be obtained from the observations\nwhen supported by ground studies. For the\nlimited preparation they received, the crewmen demonstrated\nexceptional observational ability and produced\noutstanding photographic studies. They also formulated\ncogent opinions on how to improve future observational\nand photo documentation techniques.\nSignificant research contributions to ongoing field investigations\nwere obtained from the photographs and\nobservations. These contributions were integrated into\nother aspects of the ground investigations to (1) identify\nand evaluate zones of major faulting in southeastern\nCalifornia, Baja California, and northwestern\nSonora; (2) develop a new key to the regional stratigraphy\nof the prebatholithic rocks of northern Baja\nCalifornia; (3) discover the most southwesterly known\noccurrence of Precambrian crystalline rocks in North\nAmerica; (4) discover a previously unmapped section\nof Mesozoic (?) volcanic rocks in southeastern California;\nand (5) contribute important overview perspectives\nto many regional geologic problems.\nThe experimental data and the demonstrated crew\ncapabilities justify planning future geology visual observation\nexperiments for manned Earth-orbiting programs\nsuch as the Space Shuttle. Both professional\nscientist-observers and astronaut-observers can make\ncontributions if properly prepared and equipped. The\nexperiments should be closely coordinated with active\nsurface research investigations. The emphasis should be\non selecting important problems and objectives and integrating\norbital observations and ground studies, not\non prospecting for isolated spectacular discoveries.", "publisher": "National Aeronautics and Space Administration", "publication_date": "1977-01-01" }, { "id": "authors:e91hg-a3y78", "collection": "authors", "collection_id": "e91hg-a3y78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220801-163545710", "type": "book_section", "title": "Yavapai Series; a greenstone belt", "author": [ { "family_name": "Anderson", "given_name": "C. A.", "clpid": "Anderson-C-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Wilt", "given_name": "J. C.", "clpid": "Wilt-Jan-Carol" }, { "family_name": "Jenney", "given_name": "J. P.", "clpid": "Jenney-Judith-P" } ], "abstract": "The Yavapai Series in the Prescott-Jerome area consists of two groups of volcanic and volcaniclastic rocks totalling about 40,000 feet in thickness. It is defined as a time-stratigraphic term, and Pb-U dating of zircons places the time interval from l,775 \u00b1 10 m. y. to 1,820+ m. y. Several plutons intrude the Yavapai Series, and two have Pb-U dates of 1,760 \u00b1 15 m. y. and the third pluton has an apparent age of 1 ,770 \u00b1 15 m. y. The folded and low-grade metamorphosed volcanic rocks of the Yavapai Series resemble many of the older Precambrian greenstone belts, occurring characteristically as scattered remnants in silicic cratons. Some geologists suggest that the linear pattern of these belts indicates their formation at continental-oceanic boundaries (island arcs). Other geologists suggest that downwarping and spreading of thin (or thick) sialic crusts are responsible for the location and development of the belts. There is general agreement that the mafic volcanics are the accumulation of oceanic basalts.", "publisher": "Arizona Geological Society", "publication_date": "1976-03" }, { "id": "authors:9vmat-bvb91", "collection": "authors", "collection_id": "9vmat-bvb91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151029-075342154", "type": "book_section", "title": "Structure and Petrology of the San Gabriel Anorthosite-Syenite Body, California", "author": [ { "family_name": "Carter", "given_name": "Bruce", "clpid": "Carter-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Sait\u014d", "given_name": "Tsunemasa", "clpid": "Sait\u014d-T" }, { "family_name": "Burckle", "given_name": "Lloyd Henry", "clpid": "Burckle-L-H" } ], "abstract": "The San Gabriel anorthosite \"massif\" is part of a large layered intrusive originally \u2265 10 km in thickness, part of which covers about 250 km^2 in the western San Gabriel Mountains between the San Gabriel and San Andreas fault zones 30 km north of Los Angeles. Although not subjected to post-emplacement regional metamorphism, the Precambian anorthosite is intruded by granitic rocks of Permo-Triassic and late Cretaceous ages, and is deformed by broad folds of at least two ages (Permo-Triassic (?) and mid-Cenozoic), which have produced several km of structural relief within the body. Complex Cenozoic faulting (normal and strike-slip) of several ages has strongly deformed the anorthosite, which is tectonically floored by a thick zone of mylonitized gneiss along which important post-late Cretaceous (?) thrust movement probably occurred, and at least the western part of which is underlain by a major thrust fault, as shown by the distribution of the main shock and aftershocks of the February 9, 1971 San Fernando earthquake.\nAbundant textural and structural evidence suggests that bottom crystal accumulation has produced the classic anorthosite-gabbro-syenite differentiation suite (andesine anorthosite-leuconorite-norite-jotunite-mangerite-syenite-quartz syenite) making up this body. All the rocks of this suite appear to be relatively iron-enriched; extensive deuteric uralitization of pyroxene in all but the last intruded rocks suggests that the magma probably was also relatively water-rich. In the lower part of the intrusion, extensive \"annealing\" recrystallization, especially of anorthosite, has strongly modified the original fabric of the rock. Some rocks near the top of the body (jotunite and syenite) contain small amounts of pigeonite, both in the cores of strongly zoned pigeonite-augite crystals and as uninverted remnants in hypersthene inverted from original pigeonite, suggesting a relatively shallow depth of crystallization.", "publisher": "Micropaleontology Press", "publication_date": "1972" }, { "id": "authors:zcaep-kx305", "collection": "authors", "collection_id": "zcaep-kx305", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-174058981", "type": "book_section", "title": "Pattern of faulting and nature of fault movement in the San Fernando earthquake", "author": [ { "family_name": "Kamb", "given_name": "Barclay", "clpid": "Kamb-B" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Abrams", "given_name": "M. J.", "clpid": "Abrams-M-J" }, { "family_name": "Carter", "given_name": "B. A.", "clpid": "Carter-Bruce-Alan" }, { "family_name": "Jordan", "given_name": "T. H.", "clpid": "Jordan-T-H" }, { "family_name": "Minster", "given_name": "J. B.", "clpid": "Minster-J-B" } ], "abstract": "In an effort to understand the mechanism of the February 9, 1971, San Fernando earthquake in relation to seismic observations and regional geology, we have gathered information on the occurrence and amount of ground displacement by surface faulting. Most of the field data were obtained within the first 4 days after the earthquake, because we wished to describe the fault features as much as possible in their pristine state. Systematic observations were made only in the area generally east of Sylmar and Olive View Hospital, that is, in the eastern part of the area strongly affected by the earthquake, where manifestations of surface faulting were particularly well developed. While our description of faulting is therefore limited to this area and while there doubtless are fault features that we have missed in the area studied, our results are presented here as a contribution to the general body of knowledge about the earthquake.", "publisher": "United States Geological Survey", "publication_date": "1971" }, { "id": "authors:x0ck5-13m60", "collection": "authors", "collection_id": "x0ck5-13m60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221027-152102923", "type": "book_section", "title": "Uranium-thorium-lead isotopes in some Tranquillity Base samples and their implications for lunar history", "book_title": "Proceedings of the Apollo 11 Lunar Science Conference", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "CT-Th-Pb isotopic studies of four rocks, a breccia, and lunar fines yield: (1) U (ppm) in 4 rocks average 0\u00b753; breccia, 0\u00b766; fines, 0\u00b755. (2) Th (ppm) in rocks average 1\u00b790; breccia, 2\u00b702; fines, 2\u00b717. (3) Pb (ppm) in rocks average 1-11; breccia, 1\u00b786; fines, 1\u00b746. (4) Th/U for rocks is 3\u00b76; breccia, 3\u00b705; fines, 3\u00b79. U\u00b2\u00b3\u2078/Pb\u00b2\u2070\u2074 ranges from 65 to 912, and implies extreme Pb\u00b2\u2070\u2074 depletion on the moon compared to earth and meteorites. All leads are very radiogenic, 75 per cent to more than 95 per cent, and well-defined radiogenic daughter-parent relations exist. Apparent Pb\u00b2\u2070\u2077 /Pb\u00b2\u2070\u2076 ages for all four rocks range from 4\u00b713-4\u00b722 billion years and Pb-U ages are nearly concordant. \n\nU-Th-Pb systematics in the breccia and fines yield nearly concordant apparent \"ages\" at 4\u00b760-4\u00b763 billion years. These ages have no real time significance but indicate the presence of old radiogenic lead components in the composite debris. Acid leaching studies have demonstrated that the leads in the fines and breccia are mixtures of extraordinarily heterogeneous components having Pb\u00b2\u2070\u2077 /Pb\u00b2\u2070\u2076\nratios which vary by more than 50 per cent. Two ancient components, tentatively identified, are (1) old radiogenic rock leads with associated parents and (2) old parentless radiogenic leads. Model calculations which remove lead isotope components of Tranquillity Base volcanic age from the regolith, indicate an excess of radiogenic lead with a composite Pb\u00b2\u2070\u2077 /Pb\u00b2\u2070\u2076 ratio of l \u00b796 \u00b1 0\u00b7 14. This yields an apparent age of 4\u00b795 \u00b1 0\u00b7 10 billion years which would be a minimum age for the oldest debris in the regolith and, presumably, for the moon. Volatile transfer is believed responsible for the parentless leads and is suggested as a major lunar geological process.", "isbn": "9780080163925", "publisher": "Pergamon Press", "place_of_publication": "New York, NY", "publication_date": "1970-01", "pages": "1533-1574" }, { "id": "authors:2xca1-c7734", "collection": "authors", "collection_id": "2xca1-c7734", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-182658551", "type": "book_section", "title": "The relation between radioactivity and discordance in zircons", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "The use of U-Th-Pb isotope systems in zircons has been practiced for a number of years, since Tilton and Patterson first made it possible to work with microquantities of these elements with considerable precision and accuracy. I have been interested in the geochemistry of the U-Pb and Th-Pb systems, and as one phase of this interest I have been looking at the behavior of zircons in rock systems.", "publisher": "National Academy of Sciences", "publication_date": "1963" }, { "id": "authors:89md7-6t050", "collection": "authors", "collection_id": "89md7-6t050", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-152130010", "type": "book_section", "title": "The use of cogenetic uranium-lead isotope systems in zircons in geochronology", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Among the more common natural radioactivity relationships investigated in geochronology the paired uranium-lead isotope systems have always been of interest for the multiple isotopic information yielded in a single study. Even in the earliest investigations of Nier (1939) it was apparent, however, that disagreement between the apparent ages calculated from the Pb\u00b2\u2070\u2076/U\u00b2\u00b3\u2078 and Pb\u00b2\u2070\u2077/U\u00b2\u00b3\u2075 ratios was a common phenomenon. It has been definitely established that, in general, errors in analytical techniques or in the accepted values of the decay constants U\u00b2\u00b3\u2078 and U\u00b2\u00b3\u2075 of U and U are not the sources of the more serious discrepancies. It is clear that this type of age discordance is a reflection of natural disturbances of the isotopic systems during their geologic history.", "publisher": "International Atomic Energy Agency", "publication_date": "1962-11" }, { "id": "authors:18bng-7a610", "collection": "authors", "collection_id": "18bng-7a610", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220804-173708865", "type": "book_section", "title": "Geology of northwestern Baja California, Field Trip no. 5", "author": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Allison", "given_name": "Edwin C.", "clpid": "Allison-Edwin-C" }, { "family_name": "Roberts", "given_name": "Ellis R.", "clpid": "Roberts-Ellis-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Thomas", "given_name": "Blakemore E.", "clpid": "Thomas-Blakemore-E" } ], "abstract": "This trip will offer an opportunity to examine the coastal segment of the Peninsular Range Province in an area of Baja California where the stratigraphic and tectonic history of the province is far clearer than in the more highly deformed areas north of the international border. Three major rock units characterize this province: (1) pre-batholithic eugeosynclinal accumulations of volcanic and sedimentary rocks, in part metamorphosed; (2) plutonic rocks of the batholith of southern and Baja California (the Peninsular batholith); and (3) Post-batholithic sedimentary and volcanic rocks of Upper Cretaceous and Cenozoic age. In general, the high \"backbone\" of Baja California is underlain by massive batholithic rocks, whereas the foothills between the high ranges and the Pacific coast are underlain by pre-batholithic volcanic, sedimentary and metamorphic rocks. The pre-batholithic rocks have been intruded by plutons that decrease in size and abundance toward the west. Relatively unmetamorphosed prebatholithic rocks and batholithic rocks are truncated and overlain by Upper Cretaceous and Cenozoic rocks in a thin strip along the Pacific coast. Inasmuch as this trip is limited primarily to the coastal area, the batholithic rocks will be examined only in some of these smaller plutons, but the pre- and post-batholithic rocks exposed in this coastal strip are among the most revealing that are present anywhere within the Peninsular Range province.", "publisher": "San Diego State College", "publication_date": "1961-03" }, { "id": "authors:5kkdj-80r97", "collection": "authors", "collection_id": "5kkdj-80r97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-150838031", "type": "book_section", "title": "An experimental investigation of discordant isotopic ages in zircons", "author": [ { "family_name": "Deutsch", "given_name": "S.", "clpid": "Deutsch-S" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "Tilton et al. (1957) have shown the basis for interest in dating zircons and also some of the difficulties of the method. Discordance in the three ages Pb\u00b2\u2070\u2077/Pb\u00b2\u2070\u2076, Pb\u00b2\u2070\u2077/U\u00b2\u00b3\u2075, Pb\u00b2\u2070\u2078/U\u00b2\u00b3\u2078 obtained does not always receive a satisfactory geological explanation.", "publisher": "Comitato Nazionale per l'Energia Nucleare", "publication_date": "1960" }, { "id": "authors:b9rqm-aen69", "collection": "authors", "collection_id": "b9rqm-aen69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-094312456", "type": "book_section", "title": "The possibilities of obtaining long-range supplies of uranium, thorium, and other substances from igneous rocks", "author": [ { "family_name": "Brown", "given_name": "Harrison", "clpid": "Brown-Harrison" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "contributor": [ { "family_name": "Page", "given_name": "Lincoln R.", "clpid": "Page-L-R" }, { "family_name": "Stocking", "given_name": "Hobart E.", "clpid": "Stocking-H-E" }, { "family_name": "Smith", "given_name": "Harriet B.", "clpid": "Smith-H-B" } ], "abstract": "Most uranium and thorium which have been produced in the world thus far have been obtained from ores of relatively high grade. Such deposits are not very extensive and are found infrequently. When the high-grade deposits of these substances approach exhaustion, it may be that material containing these elements in low concentrations will be the ultimate source. An average granite contains about 4 ppm uranium and 12 ppm thorium. If all the uranium and thorium in 1 ton of average granite could be extracted and utilized by means of nuclear breeding, the energy output would be equivalent to that obtained by burning 50 tons of coal. Means are now available for relatively easy extraction of about one quarter of the uranium and thorium from average granite, with an energy profit per ton of rock processed equivalent to that obtained by burning 10 tons of coal. \n\nResults also indicate that a variety of both major and minor substances of industrial importance can be obtained as byproducts of uranium and thorium production from igneous rocks. The techniques required for extracting uranium and thorium from igneous rocks are wen within the realm of present mineral-dressing and industrial-chemical experience.", "publisher": "Caltech Library", "publication_date": "1956" } ]