[ { "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:3kmwx-5yh25", "collection": "authors", "collection_id": "3kmwx-5yh25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121113-154436415", "type": "article", "title": "Assessment of (U-Th)/He thermochronometry: The low-temperature history of the San Jacinto mountains, California", "author": [ { "family_name": "Wolf", "given_name": "R. A.", "clpid": "Wolf-R-A" }, { "family_name": "Farley", "given_name": "K. A.", "orcid": "0000-0002-7846-7546", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "(U-Th)/He ages have been measured on igneous apatites from the San Jacinto mountains, a high region at the junction of the Peninsular and Transverse Ranges, to investigate the potential of this technique for thermochronometry of slowly cooled rocks. Helium ages from 79 to 17 Ma are younger than ages obtained by other dating techniques, including apatite fission-track counting, and are consistent with laboratory experiments that indicate this system has a uniquely low closure temperature. Helium ages are strongly correlated with elevation and record the latest low-temperature thermal evolution of the range. They suggest relative tectonic quiescence in the latest Cretaceous through mid-Tertiary and provide no evidence for rapid unroofing of the block during this period. Nor do they obviously require a large degree of uplift associated with convergence between the Transverse and Peninsular ranges in the last few million years. Helium ages document modest westward tilting of the block (\u223c7\u00b0) and a significant vertical component of motion on the block's bounding faults after helium retention began. This work suggests that apatite helium ages record low-temperature tectonic and thermal histories that are not apparent from other dating techniques.", "doi": "10.1130/0091-7613(1997)025<0065:AOUTHT>2.3.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1997-01", "series_number": "1", "volume": "25", "issue": "1", "pages": "65-68" }, { "id": "authors:3c4be-n8d38", "collection": "authors", "collection_id": "3c4be-n8d38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140716-113219787", "type": "article", "title": "Isotopic mapping in the Peninsular Ranges Batholith", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The 1973 study of regional variations in the Sr isotopic composition and correlated trace elements in the Mesozoic granitic rocks of the central Sierra Nevada by R.W. Kistler and Z.E. Peterman was a first order contribution to the geochemistry and petrogenesis of Cordilleran batholiths. It\nestablished standards for isotopic mapping and for thoughtful interpretations of isotopic systematics which have guided all subsequent related work.", "issn": "0016-7592", "publisher": "Geological Society of America", "publication": "Abstracts with Programs - Geological Society of America", "publication_date": "1997", "series_number": "6", "volume": "29", "issue": "6", "pages": "69-69" }, { "id": "authors:a2qze-vtt20", "collection": "authors", "collection_id": "a2qze-vtt20", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121120-104629253", "type": "article", "title": "Helium diffusion and low-temperature thermochronometry of apatite", "author": [ { "family_name": "Wolf", "given_name": "R. A.", "clpid": "Wolf-R-A" }, { "family_name": "Farley", "given_name": "K. A.", "orcid": "0000-0002-7846-7546", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "To investigate the potential of the (U-Th)/He system for low-temperature thermochronometry, we have studied helium diffusion and have measured helium ages on Durango fluorapatite and on apatites from a gabbro and two tonalites from the Peninsular Ranges Batholith. Diffusivity at moderate to very low temperatures (as low as 80\u00b0C) was measured to high analytical precision using long duration incremental outgassing experiments. All four apatites displayed remarkably similar helium diffusion behavior. Helium loss apparently occurs via volume diffusion from subgrain domains (<60 \u03bcm) which are nearly identical in size in all samples. At temperatures below 290\u00b0C, diffusivity obeys a highly linear Arrhenius relationship with an implied activation energy of about 36 kcal/mol. Above this temperature, diffusivity deviates from linearity toward lower activation energies. This transition does not arise from multiple diffusion domains, but rather from a reversible change in the physical mechanism of helium diffusion. For thermochronometric purposes the high-temperature diffusion behavior is largely irrelevant because essentially no helium is retained over geologic time at temperatures above 290\u00b0C. Using the results from the low-temperature regime, all samples yield helium closure temperatures in the range 75 \u00b1 7\u00b0C. This value is independent of chemical composition and grain size of the apatites, suggesting that a single closure temperature may apply to a wide range of samples. The (U-Th)/He ages of these apatites (17\u2013120 Ma) range from a small fraction to nearly 100% of the crystallization age of their host rocks, and are consistent with a low-temperature thermochronometric interpretation. These results strongly support previous suggestions that (U-Th)/He dating of apatite can provide high precision chronometry of very low temperature geological events.", "doi": "10.1016/S0016-7037(96)00192-5", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1996-11", "series_number": "21", "volume": "60", "issue": "21", "pages": "4231-4240" }, { "id": "authors:evb39-kn857", "collection": "authors", "collection_id": "evb39-kn857", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121120-143017682", "type": "article", "title": "The effects of long alpha-stopping distances on (U-Th)/He ages", "author": [ { "family_name": "Farley", "given_name": "K. A.", "orcid": "0000-0002-7846-7546", "clpid": "Farley-K-A" }, { "family_name": "Wolf", "given_name": "R. A.", "clpid": "Wolf-R-A" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "A mathematical framework for quantitative evaluation of alpha-stopping effects on (U-Th)/He ages has been developed. Alpha stopping ranges in the ^(238)U, ^(235)U, and ^(232)Th chains vary between \u223c10 and \u223c30 \u03bcm, depending on decay energy and density/composition of the stopping medium. In the case of U- and Th-rich accessory minerals (e.g. apatite, zircon, titanite), the dominant effect of long stopping distances is alpha ejection to adjacent minerals. For grains smaller than a few hundred microns in minimum dimension, ejection effects will cause measured helium ages to substantially underestimate true ages. For example, a sphere of 100 \u03bcm radius retains only \u223c82% of its alphas. For a homogeneous distribution of parent nuclides, the fraction of alphas ejected is \u223c 1/4 of the mean alpha range multiplied by the crystal surface to volume ratio, independent of geometry. Removal of the outer 20 \u03bcm of a crystal prior to dating eliminates the region which has experienced alpha loss, but may lead to erroneous ages when crystals are strongly zoned with respect to uranium and thorium. By careful characterization of four sieved apatite separates from a single sample, we show that it is possible to accurately correct (U-Th)/He ages for alpha ejection even when ejection exceeds 35% of total decays. Our results are useful for identifying the size and shape of grains which are best suited for (U-Th)/He dating and provide the basis for correcting ages when ejection effects are significant. This work underscores that meaningful (U-Th)/He ages require either large crystals, or correction of measured ages for alpha ejection.", "doi": "10.1016/S0016-7037(96)00193-7", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1996-11", "series_number": "21", "volume": "60", "issue": "21", "pages": "4223-4229" }, { "id": "authors:69wnk-0ee96", "collection": "authors", "collection_id": "69wnk-0ee96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130510-154654100", "type": "article", "title": "Evidence for possible horizontal faulting in southern California from earthquake mechanisms", "author": [ { "family_name": "Huang", "given_name": "Weishi", "clpid": "Huang-Weishi" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Kanamori", "given_name": "H.", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "abstract": "We find that 36 of the 505 fault-plane solutions (M \u2265 3.0, 1981\u20131990) in southern California have a nodal plane dipping no more than 30 \u00b0. With the assumption of the low-angle nodal planes being the fault planes, four cross sections are constructed to show the possible horizontal faults in the middle and upper crust. More than half of these low-angle faults are located within or adjacent to the Transverse Ranges. The focal depths vary from 1 km in the southern end of the Sierra Nevada and the southwestern Mojave Desert to 20 km in the Transverse Ranges. The slip directions are also diverse. In general, east-west extensional movements are dominant in the boundary between the southern Sierra Nevada extending to the San Emigdio Mountains and the western Mojave Desert, whereas north-south compressional movements are dominant in the Transverse Ranges. In the Peninsular Ranges and the Salton Trough, both the slip directions and focal depths vary. These features suggest that seismically active low-angle faults in southern California may exist at different depths and slip in various directions. Our data do not support the existence of a regional-scale seismically active detachment in southern California. Only in the western Transverse Ranges is there some suggestion of a large detachment surface at a depth of about 13 to 14 km.", "doi": "10.1130/0091-7613(1996)024<0123:EFPHFI>2.3.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1996-02", "series_number": "2", "volume": "24", "issue": "2", "pages": "123-126" }, { "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:kmg8k-y3r32", "collection": "authors", "collection_id": "kmg8k-y3r32", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140331-160851774", "type": "article", "title": "Tertiary metamorphic core complexes in Sonora, northwestern Mexico", "author": [ { "family_name": "Nourse", "given_name": "Jonathan A.", "clpid": "Nourse-J-A" }, { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Several ranges encompassing more than 35,000 km^2 of Sonora, Mexico, contain distinctly lineated and foliated granitic and metamorphic rocks that constitute the lower plates of metamorphic core complexes. Penetrative deformation is characterized by gently dipping mylonitic foliation across which northeast trending stretching lineation is everywhere developed. Prominent northwest trending fractures, dikes, and normal faults are orthogonal to the lineation. Most kinematic indicators in lower plate mylonitic rocks record top-to-the-southwest sense of shear. Upper plate stratigraphic sequences include Mesozoic supracrustal rocks, Tertiary volcanic and sedimentary rocks, and allochthonous Precambrian basement. Tilted blocks of upper plate strata generally overlie the mylonites along gently dipping detachment faults. Previously published U-Pb and K-Ar ages from lower plate granitic orthogneisses, upper plate volcanic sequences, and crosscutting dikes constrain the time of mylonitic deformation and detachment faulting in several of these areas to late Oligocene-early Miocene. Partitioning of extensional strain in Sonora was influenced by pre-Tertiary crustal structure. The belt of core complexes developed across two contrasting blocks of continental crust separated by the N60 degrees W striking Mojave-Sonora megashear. Portions of the southern Papago block (northeast of the megashear) consisting of Jurassic magmatic are rocks and Upper Jurassic-Cretaceous siliciclastic and carbonate strata resting upon a concealed, tectonically fragmented Precambrian basement were especially susceptible to crustal attenuation. Some core complexes of the southern Papago block occur within zones trending northwest that may coincide with Late Jurassic lineaments. In the Caborca block (southwest of the megashear), core complex-related rocks and structures have not been identified where surface exposures of Middle Proterozoic basement and overlying Upper Proterozoic-Paleozoic platform strata are common. However, extensional mylonitic fabrics are locally developed along the margins of a Tertiary two-mica granite batholith. Core complexes on both sides of the megashear appear to be preferentially developed where Tertiary granites have intruded regions of crust with basement disrupted by pre-Tertiary structures. Sonoran core complexes preserve an extensional tectonic history comparable with that described from core complexes farther north in the United States and Canadian Cordillera. The timing of mid crustal extension in Sonora (25-18 Ma) is contemporaneous with the timing of core complex development in Arizona, Nevada, and Utah. Extension occurred later in these areas than in the Pacific Northwest-British Columbia region but earlier than in the Mojave Desert-Death Valley region. Middle Tertiary mylonitic fabrics of similar style and orientation have not been recognized farther south in Mexico. The southern terminus of the mid-Tertiary Cordilleran core complex belt appears to be in Sonora.", "doi": "10.1029/93TC03324", "issn": "0278-7407", "publisher": "American Geophysical Union", "publication": "Tectonics", "publication_date": "1994-10", "series_number": "5", "volume": "13", "issue": "5", "pages": "1161-1182" }, { "id": "authors:00jtv-0w351", "collection": "authors", "collection_id": "00jtv-0w351", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130510-154746884", "type": "article", "title": "Emplacement and deformation history of the western margin\n of the Idaho batholith near McCall, Idaho: Influence of a major terrane boundary", "author": [ { "family_name": "Manduca", "given_name": "Cathryn A.", "clpid": "Manduca-C-A" }, { "family_name": "Kuntz", "given_name": "Mel A.", "clpid": "Kuntz-M-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Cretaceous plutons of the western margin of the Idaho batholith were emplaced along and to the west of the major terrane boundary separating middle Proterozoic and Paleozoic continental rocks from mostly Mesozoic accreted oceanic-arc terranes of the Blue Mountain Province. This boundary is marked by a change in the lithology of pendants and inclusions within the batholith. Plutons form two newly named complexes of igneous and metamorphosed igneous rocks. The Hazard Creek Complex, emplaced west of the boundary between the oceanic arc and the continental margin, consists primarily of a series of variably deformed and metamorphosed quartz diorite to trondhjemite plutons. The Little Goose Creek Complex, which intruded the boundary between the oceanic arc and the continental margin, is primarily porphyritic granodiorite to granite orthogneiss. A preliminary U-Pb age of 111 Ma for this porphyritic orthogneiss is a minimum age for the formation of the oceanic-arc-continent boundary.\nThe plutonic rocks were deformed both during and after emplacement in response to east-west compressive stresses. Cretaceous deformation was localized along the boundary between the accreted terranes and the continental margin and is interpreted to have occurred after the formation of this boundary. The major deformation of the Hazard Creek Complex occurred during its emplacement. The dominant fabric in the Little Goose Creek Complex is due to subsolidus ductile deformation. The localization of two deformation events along the pre-existing boundary between the accreted terranes and the continental margin suggests that a terrane boundary may form a long-lasting, crustal flaw.", "doi": "10.1130/0016-7606(1993)105<0749:EADHOT>2.3.CO;2", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "1993-06", "series_number": "6", "volume": "105", "issue": "6", "pages": "749-765" }, { "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:h6w3a-vcr68", "collection": "authors", "collection_id": "h6w3a-vcr68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140115-111655716", "type": "article", "title": "Aspects of the crustal structure of the western Mojave Desert, California, from seismic reflection and gravity data", "author": [ { "family_name": "Li", "given_name": "Yong-Gang", "clpid": "Li-Y-G" }, { "family_name": "Henyey", "given_name": "Thomas L.", "clpid": "Henyey-T-L" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Seismic and gravity data taken along line 1 of the 1982 Consortium for Continental Reflection Profiling (COCORP) Mojave Desert Survey (N-S profile, \u223c30 km long) have been used to characterize the upper crust north of the San Andreas fault in the western Mojave block of southern California. Consortium for Continental Reflection Profiling seismic reflection data were reprocessed to emphasize the upper 5 seconds (two-way travel time). The resultant common depth point (CDP) sections provided starting models for generating a refined geologic cross-section using a combination of ray tracing (forward modeling) and gravity interpretation. The forward modeling was used to validate the existence of faults and constrain their dips. The gravity data were used to refine the overall model, particularly in poor data areas on the CDP sections. Gravity data, taken along three nearby profiles parallel to primary line of section, were also used to determine the structural trend. Results from the first two seconds indicate the presence of a series of ENE striking reverse faults beneath the late Tertiary and Quaternary sedimentary cover of the western Mojave. The faults dip northward and offset the sediment-basement interface. The largest such feature has an apparent throw of \u223c1.8 km and exhibits a subtle scarp at the Earth's surface suggesting Holocene displacement. The orientation of these faults, although not an instantaneous representation of the present-day stress field, is consistent with NNW compression across the western Mojave block and WNW striking San Andreas fault, as determined from nearby focal mechanisms and in situ stress measurements. The faults also appear to be closing small sedimentary basins in the Mojave block, which may have formed during an earlier extensional phase, similar to what is happening on a much larger scale in the Los Angeles basin to the south of the San Andreas fault. Reflections between 2 and 5 s, coupled with the local geology and gravity modeling, are consistent with the presence of the Pelona/Rand schist in the subsurface beneath the western Mojave. The upper surface of the schist (i.e., Vincent/Rand thrust equivalent) rises southward toward the San Andreas fault where it is displaced vertically (up to the south) at least 5 km along the E-W trending Hitchbrook fault, such that the schist crops out between the Hitchbrook and subparallel San Andreas to the south. The same structure may exist beneath the Tehachapi mountains, with the roles of the Hitchbrook and San Andreas faults played by the north and south branches of the Garlock fault, respectively. The rising or arching of the basement toward the San Andreas fault (and toward the Garlock) is not only reflected in the geology and topography local to these faults in many places but is also generally observed on seismic reflection profiles in the vicinity of these faults in the western Mojave. Furthermore, the arching is also consistent with a strong component of fault normal compression.", "doi": "10.1029/91JB02119", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1992-06-10", "series_number": "B6", "volume": "97", "issue": "B6", "pages": "8805-8816" }, { "id": "authors:gh2yj-p3h43", "collection": "authors", "collection_id": "gh2yj-p3h43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140312-075614994", "type": "article", "title": "Geochemical Logging in the Cajon Pass Drill Hole and Its Application to a New, Oxide, Igneous Rock Classification Scheme", "author": [ { "family_name": "Pratson", "given_name": "Elizabeth Lewis", "clpid": "Pratson-E-L" }, { "family_name": "Anderson", "given_name": "Roger N.", "clpid": "Anderson-R-N" }, { "family_name": "Dove", "given_name": "Roy E.", "clpid": "Dove-R-E" }, { "family_name": "Lyle", "given_name": "Mitchell", "clpid": "Lyle-M" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" }, { "family_name": "Chappell", "given_name": "Bruce W.", "clpid": "Chappell-B-W" } ], "abstract": "A new elemental oxide classification scheme for crystalline rocks is developed and applied to geochemical well logs from the Cajon Pass drill hole. This classification scheme takes advantage of measurements of elements taken by a geochemical logging tool string. It uses K_2O versus SiO_2/Al_2O_3 to distinguish between granites, granodiorites, tonalites, syenites, monzonites, diorites, and gabbros. Oxide measurements from cores are used to calibrate the elemental abundances determined from the well logs. From these logs, a detailed lithologic column of the core is generated. The lithologic column derived from the well log classification scheme is compared with a lithologic column constructed from core samples and well cuttings. In the upper 1295 m of the well, agreement between the two columns is good. Discrepancies occur from 1295 to 2073 m and are believed to be caused by the occurrence of rock types not distinguished by the classification scheme and/or the occurrence of secondary minerals. Despite these discrepancies, the well log-based classification scheme helps to distinguish changes in rock type and shows potential as an aid to the construction of lithologic columns in boreholes of crystalline rocks.", "doi": "10.1029/91JB02643", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1992-04-10", "series_number": "B4", "volume": "97", "issue": "B4", "pages": "5167-5180" }, { "id": "authors:z3mdd-jt753", "collection": "authors", "collection_id": "z3mdd-jt753", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140416-095344675", "type": "article", "title": "^(87)Sr/^(86)Sr and ^(18)O/^(16)O isotopic systematics and geochemistry of granitoid plutons across a steeply-dipping boundary between contrasting lithospheric blocks in western 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": "A spatially abrupt geochemical boundary is preserved within four plutonic complexes along the western margin of the Cretaceous Idaho Batholith near McCall, Idaho. These intrusives ranging in composition from tonalite to granite were emplaced across a regional boundary between accreted oceanic-arc terranes and the continental margin, and their isotopic, major-element, and trace-element geochemistry provide detailed information about this change in crustal characteristics at depth, indicating that the boundary is nearly vertical and extends deep into the lithosphere. The Hazard Creek complex, emplaced west of the transition in wall-rock lithology, has initial ^(87)Sr/^(86)Sr (Ri) less than 0.7045 and \u03b4^(18)O greater than 7.5, indicating little or no continental crust in its source region; however, elevated \u03b4^(18)O requires some incorporation of rocks formed or altered at the earth's surface. A large shift in Ri and \u03b4^(18)O is observed across the 5\u20138 km wide Little Goose Creek complex, which was emplaced across the wall-rock boundary. This is interpreted as mixing between: (1) a basaltic or andesitic magma with low K_2O and high Na_2O, Al_2O_3, and Sr, similar to that forming the Hazard Creek complex; and (2) materials similar to Precambrian sedimentary sedimentary rocks with low Sr, high \u03b4^(18)O (+15) and high Ri (0.83 at 100 Ma). The Payette River complex, emplaced east of the wall-rock boundary, exhibits at least one additional component with low \u03b4^(18)O (+6), moderate R_i (0.708) and mafic composition. This component is inferred to be old basaltic material in the lower crust or upper mantle similar to that inferred to be a minor part of the Peninsular Ranges Batholith in SE California (Silver et al. 1979; Hill et al. 1986). The easternmost complex in the Idaho transect is made up of granites that may contain a component of granitic cratonal basement. The entire west-to-east geochemical transition from oceanic-arc magmas to cratonal magmas takes place over a lateral distance of less than 20 km. Although the zone of transitional protolith dominated by metasedimentary rocks is unusually narrow and may have been in part tectonically removed, the striking geochemical similarities between this traverse and several other transects across much broader areas of Nevada and California suggest that the craton itself was not rifted apart, but that juxtaposition of the accreted oceanic-arc terranes occurred along the preexisting craton margin. The data confirm that the isotopic geochemistry of granitoid plutons can be used as a probe of deep lithospheric character, and that major lateral variations in the lithosphere on the order of one to two kilometers in width can be recognized in favorable circumstances.", "doi": "10.1007/BF00283324", "issn": "0010-7999", "publisher": "Springer", "publication": "Contributions to Mineralogy and Petrology", "publication_date": "1992-01", "series_number": "3", "volume": "109", "issue": "3", "pages": "355-372" }, { "id": "authors:n2460-8sp45", "collection": "authors", "collection_id": "n2460-8sp45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130514-103113195", "type": "article", "title": "The metamictization of zircon: Radiation dose-dependent structural characteristics", "author": [ { "family_name": "Woodhead", "given_name": "James A.", "clpid": "Woodhead-J-A" }, { "family_name": "Rossman", "given_name": "George R.", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "A suite of gem zircon samples from Sri Lanka has been studied using infrared (IR) spectroscopy, X-ray diffraction, and chemical analysis. The degree of metamictization of the zircon, as indicated by unit-cell parameters, increases systematically with U-Th content\nup to the point of total metamictization. The appearance of IR spectra also varies as a function of metamictization; band widths increase and intensities decrease with increasing U-Th contents. Persistence of bands related to Si-O bonds and disappearance of bands related to Zr-O bonds indicates that the structure of metamict zircon consists of distorted and disoriented isolated silica tetrahedra with few if any undisplaced Zr cations. All spectroscopic\nindicators of crystalline order show that total metamictization is reached at an accumulated radiation dosage of ~4.5 x 10^(15) alpha decay events per mg. Hydrous components enter the structure only after total metamictization, but the amounts are not correlated with U-Th content. In all cases OH was the only hydrous species detected.", "issn": "0003-004X", "publisher": "Mineralogical Society of America", "publication": "American Mineralogist", "publication_date": "1991-02", "series_number": "1-2", "volume": "76", "issue": "1-2", "pages": "74-82" }, { "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:c1ydn-s8052", "collection": "authors", "collection_id": "c1ydn-s8052", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140311-155520484", "type": "article", "title": "San Jacinto Intrusive Complex: 2. Geochemistry", "author": [ { "family_name": "Hill", "given_name": "R. I.", "clpid": "Hill-R-I" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "Rocks from three large (>100^2 km) tonalitic intrusions exposed in the San Jacinto Mountains of southern California show a restricted compositional range of between 63 and 68 wt % SiO_2 for all but volumetrically minor felsic differentiates (with Si0_2\u224870 wt %). All rocks with less than 65.5 wt % SiO_2 show linear element-element covariation. Felsic differentiates have characteristics (higher SiO_2, K_2O, Rb, Ba, U; higher and variable rare earth elements) consistent with derivation by in situ fractionation; rocks with between 65.5 and 70 wt % SiO_2 have intermediate characteristics and are interpreted as derived from liquids formed by mixing \"primitive\" liquids with fractionated liquids within an intermittently recharged, continuously solidifying magma chamber. Mafic inclusions extend the compositional trends of the mafic tonalites to 55 wt % SiO_2. The chemical variations of both inclusions and more mafic tonalites are interpreted as resulting from processes acting before injection of their parental liquids into the observed crustal magma chambers. Effects of chamber processes are minor for all but the most felsic rocks. The major effect of recharge is to buffer the thermal and chemical properties of liquids within the magma chambers, yielding large volumes of relatively homogeneous tonalite. For those elements where the bulk distribution coefficient is between about 0.5 and 2, concurrent recharge and solidification produces rocks that closely approximate the composition of the added liquids. Estimated Rayleigh numbers for these liquids are high (>10^(10)), implying convection throughout much of the solidification history of each chamber. Existence of trace element variations within analyzed rocks imply that convection was not totally efficient at homogenizing the various batches of liquid added to each chamber.", "doi": "10.1029/JB093iB09p10349", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1988-09-10", "series_number": "B9", "volume": "93", "issue": "B9", "pages": "10349-10372" }, { "id": "authors:gjm0g-2vn50", "collection": "authors", "collection_id": "gjm0g-2vn50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131031-103755851", "type": "article", "title": "San Jacinto Intrusive Complex: 3. Constraints on crustal magma chamber processes from strontium isotope heterogeneity", "author": [ { "family_name": "Hill", "given_name": "R. I.", "clpid": "Hill-R-I" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "Strontium isotope data from three large plutons interpreted as derived from dynamic magma chambers (Hill, this issue; Hill et al., this issue) show the existence of pronounced isotopic heterogeneity within each unit. Ranges of calculated initial ^(87)Sr/^(86)Sr are unit I, 0.7060\u20130.7076; unit II, 0.7060\u20130.7074; unit III, 0.7058\u20130.7073. A limited sample of mafic inclusions and dyke rocks, interpreted as samples of liquid added to the various chambers during inflation, have initial ^(87)Sr/^(86)Sr of 0.7068\u20130.7084. These variations are regular at the kilometer scale within each pluton and show no identified correlation with any other observed geochemical or petrological parameter. Slightly older small intrusions that span the compositional range olivine gabbro to granite show a systematic increase in initial ^(87)Sr/^(86)Sr from 0.7057 in the southwest to 0.7077 in the northeast, expressing the pattern previously reported for the northern 600 km of the Peninsular Ranges batholith. The Sr isotope data indicate that melt production, aggregation, transport, and crystallization processes were far from capable of completely homogenizing initial variations in initial ^(87)Sr/^(86)Sr within the liquids from which these rocks crystallized. Whole chamber convection is apparently ruled out by these data; more complex patterns, including double-diffusively induced horizontal stratification, are permitted.", "doi": "10.1029/JB093iB09p10373", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research B", "publication_date": "1988-09-10", "series_number": "B9", "volume": "93", "issue": "B9", "pages": "10373-10388" }, { "id": "authors:czwqp-8wz13", "collection": "authors", "collection_id": "czwqp-8wz13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140311-153804093", "type": "article", "title": "Petrological and geochemical investigations at the Cajon Pass Deep Drillhole", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" }, { "family_name": "Chappell", "given_name": "Bruce W.", "clpid": "Chappell-B-W" } ], "abstract": "Chemical analyses of cores from the Cajon Pass Deep Drillhole confirm vertical lithologic diversity of the basement rocks. They are metaluminous and calcalkaline; weak major element correlations with wide-ranging SiO_2 suggest they are not a simple cogenetic suite. Quartz contents correlate with the thermal gradient profile, supporting conduction as the principal thermal transport mechanism. Abundances of heat producing elements are variable and somewhat lower than average crustal values. Cross-calibration with other measures of Th, U and K are underway. Ages of surface granitoids and core 17 are late Cretaceous; other plutonic rocks appear older but late Mesozoic. Initial lead isotopic signatures of the plutonic rocks change dramatically with depth in the hole.", "doi": "10.1029/GL015i009p00961", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "961-964" }, { "id": "authors:pyrsh-8pt24", "collection": "authors", "collection_id": "pyrsh-8pt24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140311-151633689", "type": "article", "title": "The Cajon Pass Scientific Drilling Experiment: Overview of phase 1", "author": [ { "family_name": "Zoback", "given_name": "Mark D.", "orcid": "0000-0002-8851-2099", "clpid": "Zoback-M-D" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Henyey", "given_name": "Thomas", "clpid": "Henyey-T-L" }, { "family_name": "Thatcher", "given_name": "Wayne", "clpid": "Thatcher-W" } ], "abstract": "The Cajon Pass Scientific Drilling Project is a broad, interdisciplinary experiment involving over two dozen principal scientists. Phase I of drilling, coring and downhole experimentation began Dec. 8, 1986 and ended April 2, 1987 with the hole at a depth of 2115 m, 82 m of core recovered and a wide range of downhole experiments successfully completed. In this paper we briefly outline the scientific motivation for the project and provide an overview of the scientific program. We also indicate some of the varied research areas in the earth sciences where data obtained in this experiment will provide unique and important insight into active in situ processes, regional geologic structure, and rock and fluid composition and origin.", "doi": "10.1029/GL015i009p00933", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "933-936" }, { "id": "authors:w1rtz-52398", "collection": "authors", "collection_id": "w1rtz-52398", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-095829427", "type": "article", "title": "Geologic setting and lithologic column of the Cajon Pass Deep Drillhole", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" } ], "abstract": "The Cajon Pass Deep Drillhole penetrates a late Tertiary basin developed on crystalline basement in the SW Mojave Desert, 4 km from the San Andreas fault. Cores, continuous cuttings and geophysical logs from phase I show great diversity in rock types, structure, and alteration. The hole encountered Cajon formation arkoses; granodiorite/tonalite; unusual megacrystic granite and augen gneiss; granitic and pelitic gneisses with quartzite; quartzofeldspathic orthogneiss cut by sheets of hornblende gabbro; and interlayered mafic and quartzofeldspathic orthogneisses with rare calcsilicate intervals. Foliation and compositional layering have low dips throughout the column and layered gneisses contain 10-cm-scale recumbent folds. Faults and alteration zones bound several rock units with low apparent dips. Basement cores are typically cut by steep fractures, <1 mm wide, that contain zeolites\u00b1calcite or chlorite-epidote. Fractures and faults decrease in abundance with depth.", "doi": "10.1029/GL015i009p00941", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "941-944" }, { "id": "authors:3axg6-bw088", "collection": "authors", "collection_id": "3axg6-bw088", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140310-152425705", "type": "article", "title": "Lithologic column of the \"Arkoma\" Drillhole and its relation to the Cajon Pass Deep Drillhole", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" } ], "abstract": "The 1795 m \"Arkoma\" Federal 1-26 well, 48.5 m from the Cajon Pass Deep Drillhole (CPDDH), provides additional lithologic and structural data pertinent to that project. Basement surface was encountered 158 m deeper than in the CPDDH. Rock units correlate well between the holes; the offset persists to 1128 m. Below this depth both lithologic unit thicknesses and fault zones correlate between holes on subhorizontal projections. A combination of previously unrecognized high-angle and low-angle faults of several ages are required to explain the structures. Blind low angle faults may be regionally important.", "doi": "10.1029/GL015i009p00945", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "945-948" }, { "id": "authors:tz794-62f72", "collection": "authors", "collection_id": "tz794-62f72", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130513-093549509", "type": "article", "title": "Implications of zeolites and their zonation in the Cajon Pass Deep Drillhole", "author": [ { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Zeolites occur in all cores and most cuttings samples of plutonic and gneissic rock from the Cajon Pass Deep Drillhole. Laumontite or stilbite replace plagioclase and fill fractures <1 mm to several cms in width. Zeolitic alteration is most intense in faulted and fractured zones. Zeolite species are zoned vertically. Laumontite occurs to a depth of 1885 m, stilbite from 1885 m to 2080 m and laumontite again to at least 2524 m. The transition from stilbite to laumontite at 2080 m fits both extrapolated equilibria and the CPDDH P-T gradient but laumontite occurrences above 1885 m are metastable apparently reflecting rapid uplift. Radioactive accessory minerals from the wall rock surrounded by zeolites in some fractures exhibit red-brown haloes. Halo intensity correlates to mineral radioactivity and may allow dating of mineraliztion. Observation in the CPDDH suggest a potential role for zeolites in determining chemical and physical properties such as pore water composition, seismic velocity, and gravity contrasts in faults of the San Andreas system.", "doi": "10.1029/GL015i009p00973", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "973-976" }, { "id": "authors:ejt6s-2d544", "collection": "authors", "collection_id": "ejt6s-2d544", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130621-145700946", "type": "article", "title": "Elemental and mineralogical analyses using geochemical logs from the Cajon Pass Scientific Drillhole, California, and their preliminary comparison with core analyses", "author": [ { "family_name": "Anderson", "given_name": "Roger N.", "clpid": "Anderson-R-N" }, { "family_name": "Dove", "given_name": "Roy E.", "clpid": "Dove-R-E" }, { "family_name": "Broglia", "given_name": "Cristina", "clpid": "Broglia-C" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "James", "given_name": "Eric W.", "clpid": "James-E-W" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" } ], "abstract": "Estimates of elemental and mineralogical abundances from geochemical logs are compared to preliminary chemical and modal analyses from cores in the Cajon Pass Scientific Drillhole. Accuracies of log-computed weight percent oxide and mineralogy determinations range from 10 to 30%.", "doi": "10.1029/GL015i009p00969", "issn": "0094-8276", "publisher": "American Geophysical Union", "publication": "Geophysical Research Letters", "publication_date": "1988-08", "series_number": "9", "volume": "15", "issue": "9", "pages": "969-972" }, { "id": "authors:6jfyr-5hp53", "collection": "authors", "collection_id": "6jfyr-5hp53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-945022900", "type": "article", "title": "The Peninsular Ranges Batholith: an insight into the evolution of the Cordilleran batholiths of southwestern North America", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-Bruce-W" } ], "abstract": "The Peninsular Ranges Batholith of southern and Baja California is the largest segment of a Cretaceous magmatic arc that was once continuous from northern California to southern Baja California. In this batholith, the emplacement of igneous rocks took place during a single sequence of magmatic activity, unlike many of the other components of the Cordilleran batholiths which formed during successive separate magmatic episodes. Detailed radiometric dating has shown that it is a composite of two batholiths. A western batholith, which was more heterogeneous in composition, formed as a static magmatic arc between 140 and 105 Ma and was intrusive in part into related volcanic rocks. The eastern batholith formed as a laterally transgressing arc which moved away from those older rocks between 105 and 80 Ma, intruding metasedimentary rocks. Rocks of the batholith range from undersaturated gabbros through to felsic granites, but tonalite is the most abundant rock throughout. Perhaps better than elsewhere in the Cordillera, the batholith shows beautifully developed asymmetries in chemical and isotopic properties. The main gradients in chemical composition from W to E are found among the trace elements, with Ba, Sr, Nb and the light rare earth elements increasing by more than a factor of two, and P, Rb, Pb, Th, Zn and Ga showing smaller increases. Mg and the transition metals decrease strongly towards the E, with Sc, V and Cu falling to less than half of their value in the most westerly rocks. Oxygen becomes very systematically more enriched in \u00b9\u2078O from W to E and the Sr, Nd and Pb isotopic systems change progressively from mantle values in the W to a more evolved character on the eastern side of the batholith. In detail the petrogenesis of the Peninsular Ranges Batholith is not completely understood, but many general aspects of the origin are clear. The exposed rocks, particularly in the western batholith, closely resemble those of present day island arcs, although the most typical and average tonalitic composition is distinctly more felsic than the mean quartz diorite or mafic andesite composition of arcs. Chemical and isotopic properties of the western part of the batholith indicate that it formed as the root of a primitive island arc on oceanic lithosphere at a convergent plate margin. Further E, the plutonic rocks appear to have been derived by partial melting from deeper sources of broadly basaltic composition at subcrustal levels. The compositional systematics of the batholith do not reflect a simple mixing of various end-members but are a reflection of the differing character of the source regions laterally and vertically away from the pre-Cretaceous continental margin.", "doi": "10.1017/s0263593300014152", "issn": "1755-6910", "publisher": "Cambridge University Press", "publication": "Earth and Environmental Science Transactions of the Royal Society of Edinburgh", "publication_date": "1988", "series_number": "2-3", "volume": "79", "issue": "2-3", "pages": "105-121" }, { "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:v0358-9jz10", "collection": "authors", "collection_id": "v0358-9jz10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130508-152220795", "type": "article", "title": "Comment and Reply on \"Late Triassic paleogeography of the southern Cordillera:\n The problem of a source for voluminous volcanic detritus in the Chinle Formation\n of the Colorado Plateau region\"", "author": [ { "family_name": "Stewart", "given_name": "John H.", "clpid": "Stewart-J-H" }, { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Haxel", "given_name": "Gordon B.", "clpid": "Haxel-G-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Wright", "given_name": "James E.", "clpid": "Wright-J-E" } ], "abstract": "On page 569 of our article (Stewart et al., 1986) we emphasized the\ncritical dependence of our ideas upon the validity of the isotopic and\npaleontologic geochronology, and on the calibration between the two\nmethods. Wyman also emphasizes this same point but introduces other\ninformation\u2014namely, isotopic dates on uranium ores in the Chinle Formation.\nHe indicates, citing the work of Miller and Kulp (1963), that the\naverage date for uranium ores in the Chinle Formation in the Cameron\narea, Arizona, is 175 Ma and in Lisbon Valley, Utah, is 150 Ma. These\naverages, however, seem meaningless because they incorporate individual\ndates that range from 101 to 218 Ma at Cameron, and from 95 to 207 Ma at Lisbon Valley. In any case, recent data (not cited by Wyman) gives a\nconcordant U-Pb age of 206 \u00b11 Ma for uranium ores from the Chinle\nFormation in Lisbon Valley (Ludwig et al., 1986).", "doi": "10.1130/0091-7613(1987)15<578a:CAROLT>2.0.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1987-06", "series_number": "6", "volume": "15", "issue": "6", "pages": "578-579" }, { "id": "authors:3zv2f-kzy68", "collection": "authors", "collection_id": "3zv2f-kzy68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140415-090105736", "type": "article", "title": "REE Variations Across the Peninsular Ranges Batholith: Implications for Batholithic Petrogenesis and Crustal Growth in Magmatic Arcs", "author": [ { "family_name": "Gromet", "given_name": "L. Peter", "clpid": "Gromet-L-Peter" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Rare earth element (REE) patterns of plutonic rocks across the Cretaceous Peninsular Ranges batholith vary systematically west to east, transverse to its long axis and structural trends and generally parallel to asymmetries in petrologic, geochronologic and isotopic properties. The batholith can be divided into three distinct parallel longitudinal regions, each defined by distinct REE pattern types. An abrupt transition occurs between rocks with slightly fractionated REE patterns in the western (coastal) region and rocks with middle to heavy REE fractionated and depleted patterns in the central region. Further to the east a second transition to strongly light REE enriched rocks occurs. The slopes of the REE patterns within each of these regions are largely independent of rock type. The first REE transition is closely coupled to regional discontinuities in other parameters: elimination of negative Eu anomalies, an increase in Sr content, and a marked restriction in petrologic diversity. This transition occurs over a range of initial ^(87)Sr/^(86)Sr ratios and \u03b4^(18)O values, but approximately correlates to a major shift in the emplacement style of the batholith from a stationary arc to a rapidly eastward-migrating (cratonward) arc. \n\nThe sense of the regionally consistent REE trends cannot be explained by crystallization, assimilation, combined crystallization-assimilation, or mixing processes. The consequences of assimilation and high-level differentiation are not observed generally, despite the sensitivity of the REE to these processes. Geochemical and petrological features argue that the partial melting of mafic source rocks in which plagioclase-rich (gabbroic) residual assemblages abruptly gave way laterally and downward to garnet-bearing (eclogitic) residual assemblages produced all the changes associated with the first REE transition. The change in residual assemblages from gabbroic to eclogitic was superimposed on source regions already zoned in light REE abundances, \u2078\u2077Sr/\u2078\u2076Sr and \u00b9\u2078O. Temperature and pressure constraints on the source regions place them in a subcrustal location. The calcic nature of the batholith and the dominance of tonalite and low-K\u2082O granodiorite in all its regions argue that the source materials are broadly basaltic in composition. Experimental studies are consistent with the generation of the abundant tonalitic magmas by the partial melting of basalt under both low and high pressure conditions. Arc basalts such as those commonly erupted in modern island arcs and continental margins are inferred to have provided much of the source material and the heat. Additional high-\u00b9\u2078O components are needed in the more easterly source regions. These materials must be distributed so as to contribute equally to the range of magmas that occur in a given local region, and must preserve the calcic nature of batholithic sources. Altered basalts of ancient oceanic crust and possibly their associated metasediments, previously incorporated into the lithosphere beneath the continental margin during earlier cycles of subduction, most readily satisfy these constraints. \n\nThe REE geochemistry of the central and eastern regions of the batholith differs from that of oceanic island arcs in the presence of strongly heavy REE depleted and fractionated magmas. A model is proposed in which arc basalts accumulate beneath a crustal layer. Melting of accumulated material at low pressure produces magmas of the western region. Where thickening of the basaltic underplate is sufficient to form eclogitic assemblages, eclogite-derived magmas of the central and eastern region are produced. The abrupt transition to eclogite-derived magmas that suggests a process driven by a density instability is responsible for their origin. \n\nThe Peninsular Ranges batholith appears to be representative of a major differentiation process in which mantle-derived basalt is remelted, contributing its more sialic fractions to the continental crust and leaving its mafic to ultramafic residues in the mantle. This process preserves the sialic character of the continental crust and may play a significant role in its growth and evolution. The batholith and the processes that produced it may be a more appropriate basis than immature oceanic island arcs on which to construct models of continental growth and evolution.", "doi": "10.1093/petrology/28.1.75", "issn": "0022-3530", "publisher": "Oxford University Press", "publication": "Journal of Petrology", "publication_date": "1987-02", "series_number": "1", "volume": "28", "issue": "1", "pages": "75-125" }, { "id": "authors:2pw20-7w698", "collection": "authors", "collection_id": "2pw20-7w698", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130708-154037504", "type": "article", "title": "Comment and Reply on \"S-type granites and their probable absence in southwestern North America\"", "author": [ { "family_name": "White", "given_name": "A. J. R.", "clpid": "White-A-J-R" }, { "family_name": "Clemens", "given_name": "J. D.", "clpid": "Clemens-J-D" }, { "family_name": "Holloway", "given_name": "J. R.", "clpid": "Holloway-J-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" }, { "family_name": "Wall", "given_name": "V. J.", "clpid": "Wall-V-J" } ], "abstract": "The problem of muscovite in granites is also raised by Dickson.\nMuscovite is common in felsic S-type granites, as stated by Chappell and\nWhite (1974), but how much is primary and how much is secondary are\ndebatable. We currently think that very little is primary (above the solidus).\nWe are not arguing that muscovite (whether primary or secondary),\ngarnet, and andalusite are not found in S-types; we are arguing that these\nminerals may also be found in some I-types. Dickson is quite correct in\nsaying that replacement of cordierite by micas results from hydration,\nwhich may also affect the alkali/aluminum ratio of the rock. However,\nhe is not necessarily correct in his assertion that water must be introduced\ninto the system; it may be magmatic water released from the\nmagma near the solidus during cooling and crystallization. More systematic\ngoechemical and isotopic work is required on petrographically well-documented\ngranite suites before this question is resolved.", "doi": "10.1130/0091-7613(1986)14<895:CAROSG>2.0.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1986-10", "series_number": "10", "volume": "14", "issue": "10", "pages": "895-895" }, { "id": "authors:hevf7-hjt27", "collection": "authors", "collection_id": "hevf7-hjt27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130513-090131521", "type": "article", "title": "Comment and Reply on \"S-type granites and their probable absence in southwestern North America\"", "author": [ { "family_name": "White", "given_name": "A. J. R.", "clpid": "White-A-J-R" }, { "family_name": "Clemens", "given_name": "J. D.", "clpid": "Clemens-J-D" }, { "family_name": "Holloway", "given_name": "J. R.", "clpid": "Holloway-J-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" }, { "family_name": "Wall", "given_name": "V. J.", "clpid": "Wall-V-J" } ], "abstract": "Miller's Comment highlights the necessity of clarifying the use of the\nterm S-type granite. We here make some further points.", "doi": "10.1130/0091-7613(1986)14<805:CAROSG>2.0.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1986-09", "series_number": "9", "volume": "14", "issue": "9", "pages": "805-806" }, { "id": "authors:79zj7-bbr66", "collection": "authors", "collection_id": "79zj7-bbr66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130508-152950143", "type": "article", "title": "Late Triassic paleogeography of the southern Cordillera: The problem of a source for voluminous volcanic detritus in the Chinle Formation of the Colorado Plateau region", "author": [ { "family_name": "Stewart", "given_name": "John H.", "clpid": "Stewart-J-H" }, { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Haxel", "given_name": "Gordon B.", "clpid": "Haxel-G-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Wright", "given_name": "James E.", "clpid": "Wright-J-E" } ], "abstract": "The Upper Triassic Chinle Formation of the Colorado Plateau contains voluminous volcanic detritus evidently derived from a source to the south. Volcanic rocks exposed in southern Arizona and northern Sonora have been assumed to represent this source terrane, but U-Pb isotopic geochronology and regional stratigraphic correlations indicate that these volcanic rocks are distinctly younger than the Chinle, and thus not a source for the volcanic detritus in the Chinle. Igneous rocks of known or possible Late Triassic age in Nevada, California, or northeastern Mexico are possible sources, but a clearly defined source terrane for the volcanic detritus in the Chinle has not been identified. Tectonic removal of the source terrane by rifting or strike-slip offset, though not proven, is a possibility.", "doi": "10.1130/0091-7613(1986)14<567:LTPOTS>2.0.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1986-07", "series_number": "7", "volume": "14", "issue": "7", "pages": "567-570" }, { "id": "authors:dtg07-0bp21", "collection": "authors", "collection_id": "dtg07-0bp21", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130808-083358812", "type": "article", "title": "S-type granites and their probable absence in southwestern North America", "author": [ { "family_name": "White", "given_name": "A. J. R.", "clpid": "White-A-J-R" }, { "family_name": "Clemens", "given_name": "J. D.", "clpid": "Clemens-J-D" }, { "family_name": "Holloway", "given_name": "J. R.", "clpid": "Holloway-J-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" }, { "family_name": "Wall", "given_name": "V. J.", "clpid": "Wall-V-J" } ], "abstract": "Criteria that have been (and still are) used to characterize S-type granites of the Lachlan Fold Belt (LFB) of southeastern Australia are reviewed, and comparisons are made with various peraluminous granites of southwestern North America, some of which have been classified as S-types on the basis of insufficient data. \n\nVirtually all of the vast volume of S-type granites in the LFB are near-surface, batholithic granites that are commonly associated with S-type volcanics and are not associated with regional metamorphic rocks and migmatites. They are strongly peraluminous, as shown by the presence of cordierite. Granites with primary muscovite are rare. All are low in Na, Ca, and Sr as a result of chemical weathering during formation of the sedimentary sources. Peraluminous granites of various ages in southwestern North America are distinctly different. They rarely contain cordierite (a mineral characteristic of LFB S-types), but some are highly evolved such that Fe-Mn-rich garnet has crystallized. They are dominantly two-mica granites, indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the LFB. Cordierite-bearing volcanics (S-types) have not been reported. Sodium is generally high in the peraluminous granites of southwestern North America. Some of these rocks have trondhjemitic affinities; the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks. Locally, some peraluminous rocks (marginal to metaluminous types) may owe their compositions to high-level contamination of I-types; these are not S-type rocks. No compelling evidence has been presented that any of the peraluminous granites of southwestern North America are S-types.", "doi": "10.1130/0091-7613(1986)14<115:SGATPA>2.0.CO;2", "issn": "0091-7613", "publisher": "Geological Society of America", "publication": "Geology", "publication_date": "1986-02", "series_number": "2", "volume": "14", "issue": "2", "pages": "115-118" }, { "id": "authors:3y964-9s806", "collection": "authors", "collection_id": "3y964-9s806", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151022-132313827", "type": "article", "title": "The border connection; geological correlations and contrasts between Arizona and Sonora", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The same tectonostratigraphic evolution characterizes a broad belt of rocks centered along the border between Arizona and Sonora. Differences are evident in areas tens of kilometers north and south of the border region. No counterpart of the stable Colorado Plateau north of the border belt exists in Sonora. Terranes, south of the border belt, are separated by faults or less obvious discontinuities in structural, stratigraphic and isotopic patterns. Directions of movement on postulated faults are hotly debated. Locally, where terrane borders are strongly obscured by subsequent tectonism, volcanism, intrusion and/or sedimentation, they are almost mystical or mythical. Tests of the hypothesis that some of the terranes record hundreds of kilometers of left-lateral offset have been undertaken. Although the results are not\nprobative, they are very supportive.", "issn": "0066-7412", "publisher": "Arizona Geological Society", "publication": "Arizona Geological Society Digest", "publication_date": "1986", "volume": "16", "pages": "72-73" }, { "id": "authors:b9jqz-pma80", "collection": "authors", "collection_id": "b9jqz-pma80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131120-102544794", "type": "article", "title": "Coupled Sr-O isotope variations as an indicator of source heterogeneity for the Northern Peninsular Ranges batholith", "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" } ], "abstract": "Primary \u03b4^(18)O values for tonalitic rocks from the San Jacinto Intrusive Complex range from +9.0 to +10.6; initial ^(87)Sr/^(86)Sr for the same samples varies from 0.7058 to 0.7076. Rocks with low \u03b4^(18)O tend to have higher initial ^(87)Sr/^(86)Sr. The majority of samples have a limited range of \u03b4^(18)O values (+10.0\u2013+10.4) that is anticorrelated with colour index; this variation is compatible with crystallization of rocks with varying mineral abundances from an homogeneous (for oxygen) reservoir. More mafic rocks show a large range of \u03b4^(18)O values, reflecting original variations in source material compositions. The combined Sr-O isotope data demonstrate that three or more distinct components were involved in the genesis of these rocks; these three components are also seen in batholithic rocks from the Mojave Block and Sierra Nevada to the north. These data are interpreted as indicating a 0\u201335% (oxygen atom basis) contribution to the San Jacinto rocks from an old continental lithosphere source.", "doi": "10.1007/BF00572164", "issn": "0010-7999", "publisher": "Springer", "publication": "Contributions to Mineralogy and Petrology", "publication_date": "1986", "series_number": "3", "volume": "92", "issue": "3", "pages": "351-361" }, { "id": "authors:9s5r3-4mt78", "collection": "authors", "collection_id": "9s5r3-4mt78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140311-101114151", "type": "article", "title": "Solidification and recharge of SiO_2-rich plutonic magma chambers", "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": "Chappell", "given_name": "B. W.", "clpid": "Chappell-B-W" }, { "family_name": "Taylor", "given_name": "H. P., Jr.", "clpid": "Taylor-H-P-Jr" } ], "abstract": "There exists substantial variation in initial strontium isotopic composition in rocks from three otherwise homogeneous tonalite plutons. We interpret disrupted dykes as conduits through which heterogeneous liquids were added periodically to the inflating magma chambers. Recharge buffered the physicochemical but not the strontium isotope properties of the crystallizing liquids.", "doi": "10.1038/313643a0", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "1985-02-21", "series_number": "6004", "volume": "313", "issue": "6004", "pages": "643-646" }, { "id": "authors:80k1g-3g949", "collection": "authors", "collection_id": "80k1g-3g949", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131113-090618069", "type": "article", "title": "Rare earth element distributions among minerals in a granodiorite and their petrogenetic implications", "author": [ { "family_name": "Gromet", "given_name": "L. Peter", "clpid": "Gromet-L-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "A study of the distribution of lanthanide rare earths in a granodiorite from the eastern Peninsular Ranges batholith, southern California, reveals that a large fraction of the REE in this rock resides in the accessory phases sphene and allanite. The minerals plagioclase, alkali feldspar, biotite, epidote and apatite each contribute approximately 1% or less of each REE to the whole rock, with the exception of Eu for which plagioclase contributes 7%. Sphene and allanite together contain 80% to 95% of each REE. Each of these phases is zoned in REE concentration with substantial decreases from core to margin. Textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma. REE zoning trends in sphene and allanite, and unexpectedly low REE concentrations in largely later crystallizing minerals such as feldspar, indicate that the precipitation of sphene and allanite significantly reduced REE concentrations in residual melts. These results illustrate the potential that sphene and allanite have for controlling the behavior of REE in granitic magmas.\n\nAvailable information collectively suggest that the sampled granodiorite existed as a complete melt, that the REE contained in the assemblage of phases were derived by direct crystallization from the melt, and that the melt behaved essentially as a closed system once crystallization of the phases now present began. Close correspondences between the major and trace element chemistries of the granodiorite and phenocryst-poor lavas from similar tectonic settings support these conclusions. The REE pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism. The high liquidus temperature of a granodiorite melt (~ 1000\u00b0C) indicates the importance of mantle-derived components within the sources of batholithic magmas in the Peninsular Ranges.", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1983-05", "series_number": "5", "volume": "47", "issue": "5", "pages": "925-939" }, { "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: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: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:1n67p-4mg26", "collection": "authors", "collection_id": "1n67p-4mg26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-110115541", "type": "article", "title": "An overview of Precambrian rocks in Sonora", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The oldest stratified rocks recognized in NW Sonora (and in Mexico) are deformed muscovite-quartz schists, quartzites, and biotite-quartzofeldspathic gneisses near Caborca, which are cut by calcalkaline intrusives ranging from 1,710 to 1,750 m.y. in age. Southwest of Caborca, upper amphibolite facies layered quattzofeldspathic and amphibolitic gneisses were apparently deformed and metamorphosed at about 1,660 \u00b1 15 m.y. ago, concealing original lithologies and ages. In northeastern Sonora, a younger belt of eugeosynolinal strata, about 1,680 \u00b1 20 m. y. old was tightly\nfolded and metamorphosed to greenschist facies about 1,650 m.y. ago. Numerous granitic plutons intruded into the older Precambrian crust about 1,410 to 1,440 m.y. ago. These major intrusive masses are not known to have been accompanied by regional sedimentation or deformation. Rare, small plutons of micrographic granite added to the Precambrian crystalline complexes about 1,100 m.y. ago, are the youngest Precambrian igneous rocks recognized. They limit the age of a thick miogeoclinal sequence of unmetamorphosed quartzose sandstones, carbonates with numerous stromatolite horizons, and shales which rest nonconformably on them. The sequence is overlain without unconformity by a fossiliferous Lower Cambrian section. The northwestern and northeastern Precambrian suits appear to be separated by a Jurassic magmatic arc and a postulated shear structure of large lateral displacement. Both suites correlate northward into related belts in the SW United States. To the east they are concealed by Phanerozoic cover. Abrupt\ntermination of Precambrian exposures south and west suggests major younger tectonic features which we suspect played important but undefined roles in the apparent absence of Precambrian basement under much of northern and west-central Mexico.", "issn": "0185-0962", "publisher": "Universidad Nacional Aut\u00f3noma de Mexico", "publication": "Revista Mexicana de Ciencias Geol\u00f3gicas", "publication_date": "1981", "series_number": "2", "volume": "5", "issue": "2", "pages": "131-139" }, { "id": "authors:3vq2g-9xd29", "collection": "authors", "collection_id": "3vq2g-9xd29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170728-143702956", "type": "monograph", "title": "Uranium in granites from the Southwestern United States: actinide parent-daughter systems, sites and mobilization. First year report", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Williams", "given_name": "I. S.", "clpid": "Williams-I-S" }, { "family_name": "Woodhead", "given_name": "J. A.", "clpid": "Woodhead-J-A" } ], "abstract": "Some of the principal findings of the study on the Lawler Peak Granite are: the granite is dated precisely by this work at 1411 \u00b1 3 m.y., confirming its synchroneity with a great regional terrane of granites. Uranium is presently 8-10 times crustal abundance and thorium 2-3 times in this granite. Uranium is found to be enriched in at least eight, possibly ten, primary igneous mineral species over the whole-rock values. Individual mineral species show distinct levels in, and characteristics ranges of, uranium concentration. It appears that in a uraniferous granite such as this, conventional accuracy mineral suites probably cannot account for most of the uranium in the rock, and more rare, high U-concentration phases also are present and are significant uranium hosts. It appears that at least two different geological episodes have contributed to the disturbance of the U-Th-Pb isotope systems. Studies of various sites for transient dispersal of uranium, thorium, and radiogenic lead isotopes indicate a non-uniform dispersal of these components. It appears that the bulk rock has lost at least 24 percent of its original uranium endowment, accepting limited or no radiogenic lead or thorium migration from the sample.", "publisher": "Caltech Library", "publication_date": "1980-10" }, { "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: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: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:0azx9-sxr15", "collection": "authors", "collection_id": "0azx9-sxr15", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220725-222050953", "type": "monograph", "title": "Testimony before the Congressional Committee on Science and Technology. Subcommittee On Energy Research And Production", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Any analysis of the problems of uranium supply and demand for the United States nuclear power industry must take cognizance of the recent national trauma over the nuclear reactor accident in Three Mile Island, Pennsylvania. National policy decisions on nuclear power will be made with this incident prominently in the foreground. It is essential that a balanced view of all aspects of the availability of energy supplies be maintained during these considerations. \n\nNuclear energy can provide an important supply of electricity for which the true costs must include uncertainties and risks of several kinds. It is clear, also, that no other major source of energy is without some form of significant risk and considerable uncertainty about the timeliness of availability, cost to the immediate environment, and ultimate cost to society. In this discussion, no special advocacy for an enlarged role for nuclear power is intended. It is based upon what I believe to be a reasonable, pragmatic utilization of the present large investments in nuclear energy power systems with all appropriate care in the face of a growing world energy shortage. \n\nPerceptions of the requirements of natural uranium for the United States nuclear power industry have undergone significant modification in the last few years. The Department of Energy has continued to reduce its projections of installed nuclear generating capacity from year to year, as shown in Table 1.", "publisher": "Caltech Library", "publication_date": "1979-05-31" }, { "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:6eh48-b5e75", "collection": "authors", "collection_id": "6eh48-b5e75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131112-134631506", "type": "article", "title": "Lead-isotope inhomogeneity in Precambrian igneous K-feldspars", "author": [ { "family_name": "Ludwig", "given_name": "Kenneth R.", "clpid": "Ludwig-K-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Stepwise Pb-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognized. One has a \"normal\" isotopic composition, with relative abundances of ^(206)Pb, ^(207)Pb and ^(208)Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure ^(206)Pb, derived from long-term migration and accumulation of radioactive daughter(s) of ^(238)U. This \"pure ^(206)pb\" lead occupies different sites from the \"normal\" radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150\u00b0C.\nThe usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks.", "doi": "10.1016/0016-7037(77)90251-4", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1977-10", "series_number": "10", "volume": "41", "issue": "10", "pages": "1457-1471" }, { "id": "authors:eetxt-05z27", "collection": "authors", "collection_id": "eetxt-05z27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220718-988950100", "type": "article", "title": "U-Pb isotope ages of granitic plutons near Cananea, Sonora", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-Thomas-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The Cananea \"granite\" crops out in the Cananea mining district, which includes some of the most important known copper deposits in Mexico. The area is in northern Sonora, approximately 100 km southeast of the twin cities of Nogales, Arizona-Sonera, on the international border.By means of isotopic analyses of U-Pb systems in cogenetic suites of zircon from two different phases of the pluton, its interpreted age has been firmly established at 1,440 + or - 15 m.y. Cananea granite, actually a quartz monzonite, is lithologically characteristic of a major Precambrian suite of anorogenic, consanguineous plutons of porphyritic granodiorite to granite. Constituents of this previously recognized series, which crop out throughout the southwestern U. S. and into northern Mexico, consistently yield zircon radiometric ages within the interval 1,425-1,475 m.y.Major younger intrusions in and nearby the Cananea district include Cuitaca granodiorite and Chivato monzodiorite. These bodies yield apparent zircon ages of 64 + or - 3 and 69 + or - 1 m.y., respectively. Although more precise geochronologic relationships between young plutons, the adjacent layered sequence, and cross-cutting, brecciated, quartz porphyry plugs are needed, correlation exists between major plutonism and mineralization.The Precambrian age of the Cananea granite precludes its chronological association with the younger mineralized plugs and should be taken into account in future planning of exploration.", "doi": "10.2113/gsecongeo.72.5.827", "issn": "1554-0774", "publisher": "Society of Economic Geologists", "publication": "Economic Geology", "publication_date": "1977-08-01", "series_number": "5", "volume": "72", "issue": "5", "pages": "827-836" }, { "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:15yne-hpn18", "collection": "authors", "collection_id": "15yne-hpn18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130515-071510683", "type": "article", "title": "Rubidium-Strontium Fractionation Domains in the Peninsular Ranges Batholith and Their Implications for Magmatic Arc Evolution", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Early", "given_name": "Thomas O.", "clpid": "Early-T-O" } ], "abstract": "The northern 600 km of this Cretaceous batholith,\ncomprised of hundreds of diverse plutons, appears to\nconsist of 12-15 domains. Each domain is a region\nwhere rocks of all types (within our limited sampling)\nshow a regular linear covariation of Rb and Sr concentrations. This regularity displays different concentration levels and a different slope and is accompanied by a distinct set of isotopic systematics in each domain. The domains do not disrupt the remarkable zonation of initial Sr ratios in the batholith (Early and Silver, 1973). No independent field or petrographic recognition of the Rb-Sr characterized entities has been mode. Very similar rocks occur in adjacent domains. Domains are equant or elongate NNW, up to 200 km long and 30 km\nwide, parallel to regional tectonic grain. Each domain\nis interpreted as a region of magmas sampled or differentiated from a mantle source reservoir possessing characteristic trace element levels and Sr isotopic properties. An apparent age of reservoir formation and isolation prior to fractionation and crustal emplacement and on apparent initial Sr ratio at the time of reservoir isolation can be derived for each domain. There is no strong correlation between reservoir apparent ages and initial ratios. Mixing systems involving older granitic crust with primitive mantle seem precluded. We identify\nsimilar domains characterized by R-Sr systematics in\nother batholithic and volcanic complexes. We infer these domains to be fundamental loci of chemistry and energy from which magmatic arcs are constructed.", "issn": "0002-8606", "publisher": "American Geophysical Union", "publication": "Transactions - American Geophysical Union", "publication_date": "1977", "series_number": "6", "volume": "58", "issue": "6", "pages": "532" }, { "id": "authors:05feg-cw329", "collection": "authors", "collection_id": "05feg-cw329", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130514-135353772", "type": "article", "title": "Geographic Variation of Rare Earth Fractionations in Plutonic Rocks Across the Peninsular Ranges Batholith, Southern California", "author": [ { "family_name": "Gromet", "given_name": "L. Peter", "clpid": "Gromet-L-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Rare earth element patterns of plutonic rocks (chondrite-\nnormolized) across the Peninsular Ranges batholith vary systematically west to east, transverse to the long axis and structural trends and parallel to known asymmetries\nin petrologic, geochronologic, and Sr isotopic properties. The abundant tonolites in the western region are characterized by slight light REE enrichment relative to heavy REE. Eastward, patterns become more highly\nfractionated, showing light REE enrichment and heavy\nREE depletion. The slope of patterns at any geographic\nlocation are largely independent of rock type. However,\nlocally, certain silica- saturated and undersaturated\ngabbros may show divergent trends. The relative fractionation among the middle and heavy REE indicates\ndifferentiation processes involving the observed major\nphases such as hornblende and plagioclase are not important\nin producing the basic geographic trends. They may\nbe reflected in more local lithologic variations. The\npronounced geographic zonation in REE character correlates\nstrongly with Sr concentration, suggesting a common\nmechanism for their origin. The systematic nature of\nthese fractionations, their correlation with previously\nreported Sr isotopic data, and their lock of correlation\nwith lithology, argues against significant upper-crustal\ncontamination with old cratonic components. These features appear to originate in heterogeneous deep-seated sources whose sampling has been selectively activated at a convergent plate boundary.", "issn": "0002-8606", "publisher": "American Geophysical Union", "publication": "Transactions - American Geophysical Union", "publication_date": "1977", "series_number": "6", "volume": "58", "issue": "6", "pages": "532" }, { "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:w68n8-75565", "collection": "authors", "collection_id": "w68n8-75565", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130515-142928635", "type": "article", "title": "Thorium-Uranium fractionation as an indicator of petrogenetic processes", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "A mean Th/U ratio, ~4, seems to characterize most\nterrestrial, lunar, and meteoritic igneous materials and\nmajor patterns of lead isotopic evolution develop principally in systems with Th/U about 3.7-4.0. Some\nimportant crustal igneous subsystems show systematic\ndeviations from these values. Such fractionation generally\nis attributed to the geochemical behavior of the large\nlithophile actinide ions in various enriched minor phases.\nThis probably is true in highly differentiated series with\nhigher Th and U levels (>8 and 2 ppm). A different\nfractionation mechanism may be more important in some\nlower concentration systems. Isotope dilution mass spectrometric studies of U and Th in diverse igneous feldspar separates reveal significant U and Th partitioning into them with drastic fractionation of Th/U (values 0.2- 3.0). Alkali feldspars in granitic rocks display partition coefficients (feldspar/total rock) of about 0.005-0.02 for U\nand 0.001-0.004 for Th; Th/U~0.5-3.0. In plagioclase\nin gabbros, tonalites, and granodiorites with lower Th and\nU, the coefficients appear larger (U~0.1-0.4, Th~0.04-0.2) but Th/U appears lower (Th/U~0.2-2.0) than in K-feldspar. Limited data suggests some pyraxenes and other major minerals may also fractionate Th/U to lower ratios. Differences in ionic radius and uranium oxidation states may contribute to the undefined fractionation mechanism.\nProcesses of primary differentiation (fractional\ncrystallization, partial melting) involving gabbroic systems\nseem to reflect this fractionation. Oceanic tholeiites, end\nmassive gabbroic complexes display generally low Th/U\nvalues. Their lead isotopes reflect reservoirs with more\nnormal Th/U ratios. This suggests limits on the number of\nfractionation cycles, mantle mixing, and/or reservoir dimensions for primary basaltic systems. Th and U and their\nassociated lead isotope systems can be used with lanthanide\nR.E.E. to assist in developmet of petrogenetic models.", "issn": "0002-8606", "publisher": "American Geophysical Union", "publication": "Transactions - American Geophysical Union", "publication_date": "1976", "series_number": "4", "volume": "57", "issue": "4", "pages": "351" }, { "id": "authors:05681-g7165", "collection": "authors", "collection_id": "05681-g7165", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220718-375642500", "type": "monograph", "title": "Plumbotectonics IIA, Precambrian massive sulfide deposits", "author": [ { "family_name": "Stacey", "given_name": "J. S.", "clpid": "Stacey-J-S" }, { "family_name": "Doe", "given_name": "B. R.", "clpid": "Doe-B-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Zartman", "given_name": "R. E.", "clpid": "Zartman-R-E" } ], "abstract": "Professor Tugarinov has long recognized the importance of common lead in rocks and ore deposits as an age indicator. The paper he authored with L. K. Gavrilova and V. P. Bedrinov in 1963, and the work of Cantanzaro and Gast (1960), are two of the most extensive studies of the evolution of lead isotopes in feldspars. Such studies are very important to our understanding of crustal evolution because of our ability to calibrate feldspar ages by other means. The pioneer paper by Stanton and Russell (1959) opened the way for dating certain deposits submarine volcanic exhalative massive sulfide deposits in the orogene. It is now generally accepted that these deposits formed during volcanism or shortly thereafter (Hutchinson, 1973). Therefore their lead isotope evolution may be correlated with time by dating the enclosing rocks. Over the last eight years, investigators have gradually realized that lead isotopic analyses, coupled with geochronologic studies, may yield much additional information about ore deposits and their origins. \n\nThis paper evaluates the lead isotopic characteristics of Precambrian massive sulfide deposits of all types. The treatment here will be similar to that used by Doe and Zartman (1976) in their \"plumbotectonics\" model for Phanerozoic deposits of this type. The submarine volcanic exhalative ores were chosen for emphasis because they are the type class for \"conformable\" or \"stratiform\" leads used in lead isotope model theory. We suggest that any deviation from a strictly average isotopic composition for a given age of deposit can often be explained by differences in the tectonic settings in which the ores were formed. This paper is a \"state-of-knowledge\" discussion of that thesis.", "doi": "10.3133/ofr76476", "publisher": "U.S. Geological Survey", "publication_date": "1976" }, { "id": "authors:fyxbe-3m314", "collection": "authors", "collection_id": "fyxbe-3m314", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151027-140622202", "type": "monograph", "title": "Skylab-4 visual observations project: Geological features of southwestern North America", "author": [ { "family_name": "Silver", "given_name": "Leon 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" } ], "contributor": [ { "family_name": "Carr", "given_name": "G. P.", "clpid": "Carr-Gerald-P" }, { "family_name": "Gibson", "given_name": "E. G.", "clpid": "Gibson-Edward-G" }, { "family_name": "Pogue", "given_name": "W. R.", "clpid": "Pogue-William-R" } ], "abstract": "Visual observations conducted by Skylab-4 crewmen on seven designated geological target areas and other targets of opportunity in parts of southwestern United States and northwestern Mexico were described. The experiments were designed to learn how effectively geologic features could be observed from orbit and what research information could be obtained from the observations when supported by ground studies. For the limited preparation they received, the crewmen demonstrated exceptional observational ability and produced outstanding photographic studies. They also formulated cogent opinions on how to improve future observational and photo-documentation techniques. From the photographs and other observations, it was possible to obtain significant research contributions to on-going field investigations. These contributions were integrated into other aspects of the ground investigations to the following topics: major faults, regional stratigraphy, occurrence of Precambrian crystalline rocks, mapping of Mesozoic volcanic rocks, regional geology.", "publisher": "California Institute of Technology", "publication_date": "1975-11-01" }, { "id": "authors:1te6q-7mn23", "collection": "authors", "collection_id": "1te6q-7mn23", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-103915490", "type": "article", "title": "Potassic Granophyre Associated with Precambrian Diabase, Sierra Ancha, Central Arizona", "author": [ { "family_name": "Smith", "given_name": "Douglas", "clpid": "Smith-D" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Lenses of granitic and syenitic granophyre unusually rich in potassium crop out at and near the roof of a Precambrian sill complex of olivine diabase intruded into the Apache Group. The lenses locally are 45 m thick; the diabase is 210 to 240 m thick in the same area. Granophyre contains 7 to 11 wt percent K2O, whereas intruded rocks of the Dripping Spring Quartzite contain 9 to 14 wt percent K_2O. The sedimentary rocks were enriched in potassium before emplacement of diabase, probably during diagenesis while saturated with saline water. \n\nThe granophyre apparently was mostly liquid when emplaced. Chemical data, together with arguments based on mineralogy, textures, and field relations, indicate that most of the granophyre was derived from Dripping Spring Quartzite. The granophyre, however, contains more Na, Ca, and P and less K than the sedimentary rocks. Rocks representing a differentiated fraction of diabase magma are concentrated below the granophyre at the roof of the complex. The unusual crystallization profile may reflect an influx of water from the overlying sedimentary rocks into the magma. The influx of water may have been responsible for the extensive interaction between magma and country rock. Country rock fused during the interaction appears to have migrated to local structural highs. \n\nBecause the evidence that the granophyre formed largely from country-rock material is unusually clearcut, this granophyre may serve as a petrogenic model for some other silica-rich igneous rocks associated with intrusions of basaltic magma.", "doi": "10.1130/0016-7606(1975)86<503:PGAWPD>2.0.CO;2", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "1975-04", "series_number": "4", "volume": "86", "issue": "4", "pages": "503-513" }, { "id": "authors:6g885-w8469", "collection": "authors", "collection_id": "6g885-w8469", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150729-094139122", "type": "article", "title": "Apollo 16 Exploration of Descartes: A Geologic Summary", "author": [ { "family_name": "Ulrich", "given_name": "G. E.", "clpid": "Ulrich-G-E" }, { "family_name": "Rennilson", "given_name": "J. J.", "clpid": "Rennilson-J-J" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "literal": "Apollo Field Geology Investigation Team" } ], "abstract": "The Cayley Plains at the Apollo 16 landing site consist of crudely stratified breccias to a depth of at least 200 meters, overlain by a regolith 10 to 15 meters thick. Samples, photographs, and observations by the astronauts indicate that most of the rocks are impact breccias derived from an anorthosite-gabbro complex. The least brecciated members of the suite include coarse-grained anorthosite and finer-grained, more mafic rocks, some with igneous and some with metamorphic textures. Much of the traverse area is covered by ejecta from North Ray and South Ray craters, but the abundance of rock fragments increases to the south toward the younger South Ray crater. The Descartes highlands, a distinct morphologic entity, differ from the adjacent Cayley formation more in physiographic expression than in lithologic character.", "doi": "10.1126/science.179.4068.62", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1973-01-05", "series_number": "4068", "volume": "179", "issue": "4068", "pages": "62-69" }, { "id": "authors:0dcf9-5pc21", "collection": "authors", "collection_id": "0dcf9-5pc21", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141111-135550881", "type": "article", "title": "A crustal-upper-mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock Dike", "author": [ { "family_name": "McGetchin", "given_name": "Thomas R.", "clpid": "McGetchin-T-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "On the basis of the size, the abundance, and the petrographic character of xenoliths in the Moses Rock dike, a model for the vertical stratigraphy of crystalline rocks beneath the dike is proposed extending from near the surface to a depth of about 200 km. Sedimentary clasts, whose original position in the undisturbed vent walls is known but which are now within the intrusive breccia of the Moses Rock dike, show a decrease in size with distance of upward transport from their original position in the vent walls. This inverse relationship between fragment size and known depth of origin provides an empirical basis for a reconstructed model for the distribution of rocks on the basis of the particle size of fragments in the intrusive breccia. Metabasalt, granite, and granite gneiss are abundant in the upper part of the crust along the dike walls; diorite, gabbro, and amphibole schists of basic composition constitute intermediate layers, and garnet-bearing metagabbro (basic granulite gneiss) and serpentine schist are present in the lower crust. The crustal rock suite is predominantly metavolcanic and metaplutonic and basic in composition. Dense ultramafic rocks, possibly derived from the mantle, constitute about 0.3% of the breccia filling the dike and include jadeite-rich clinopyroxenite, eclogite, spinel-websterite, spinel-lherzolite, and garnet-lherzolite. The M discontinuity appraently occurs within a petrologically complex region and may coincide with phase and compositional transitions, which include hydration. A compositional transition within the upper mantle between spinel- and garnet-peridotite (lherzolite) is inferred. The variety and the abundance of ultramafic and dense types, together with the complexity of their textures, suggest that the mantle may be as complicated as the crust in composition and history.", "doi": "10.1029/JB077i035p07022", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1972-12-10", "series_number": "35", "volume": "77", "issue": "35", "pages": "7022-7037" }, { "id": "authors:vfe2y-2jg42", "collection": "authors", "collection_id": "vfe2y-2jg42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-282315900", "type": "article", "title": "Geologic Setting and Petrology of Apollo 15 Anorthosite (15415)", "author": [ { "family_name": "Wilshire", "given_name": "H. G.", "clpid": "Wilshire-H-G" }, { "family_name": "Schaber", "given_name": "G. G.", "clpid": "Schaber-G-G" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Phinney", "given_name": "W. C.", "clpid": "Phinney-W-C" }, { "family_name": "Jackson", "given_name": "E. D.", "clpid": "Jackson-E-D" } ], "abstract": "Apollo 15 sample number 15415, popularly called the \"Genesis Rock,\" is coarse-grained anorthosite composed largely of calcic plagioclase with small amounts of three pyroxene phases. The rock was found as a clast in a piece of friable soil breccia on the lip of Spur crater, a small young crater on the lower slopes of the Apennine Mountains. The mode of occurrence of sample 15415 indicates that it has undergone at least two, and possibly three or more, fragmentation events. These events are reflected in the texture of the rock by shattered and granulated minerals. An earlier thermal metamorphic event is represented by irregular bands of coarsely recrystallized plagioclase and minor pyroxene that cross larger plagioclase grains. Preliminary observations of textural relations of the large plagioclase grains are consistent either with accumulation of plagioclase followed by overgrowth of cumulus grains and post-cumulus crystallization of minor interstitial pyroxene, or with metamorphic recrystallization that eradicated original textures. Any of the events in the complex history of this rock may have affected apparent radiometric ages. Comparative abundance of similar, though smaller, pieces of anorthositic rock in the area and dominance of originally coarse-grained gabbroic-anorthositic clasts in breccia at Spur crater suggest that sample 15415 is the least-deformed member of a suite of similar rocks that were ejected from beneath the regolith at Spur crater.", "doi": "10.1130/0016-7606(1972)83[1083:gsapoa]2.0.co;2", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "1972-04", "series_number": "4", "volume": "83", "issue": "4", "pages": "1083-1092" }, { "id": "authors:qsg92-ppk63", "collection": "authors", "collection_id": "qsg92-ppk63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150729-123808643", "type": "article", "title": "Geologic Setting of the Apollo 15 Samples", "author": [ { "family_name": "Swann", "given_name": "G. A.", "clpid": "Swann-G-A" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Rennilson", "given_name": "J. J.", "clpid": "Rennilson-J-J" }, { "literal": "Apollo Lunar Geology Investigation Team" } ], "abstract": "The samples and photographs returned from the Apollo 15 site show that Hadley Delta is largely underlain by breccias whose clasts are mainly fragments of coarse-grained feldspathic rocks and nonmare-type basalt. Conspicuous sets of lineaments, visible in surface and orbital photographs of Mount Hadley and Hadley Delta, may represent systematic layering or fracture sets. The mare surface, with regolith about 5 meters thick, is underlain by two major basalt types, at least one of which has extensive lateral continuity and is exposed in the upper wall of Hadley Rille. Gradual erosional recession of the edges and filing of the interior of the rille by talus have contributed to the present cross sectional profile.", "doi": "10.1126/science.175.4020.407", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1972-01-28", "series_number": "4020", "volume": "175", "issue": "4020", "pages": "407-415" }, { "id": "authors:qcpez-8x441", "collection": "authors", "collection_id": "qcpez-8x441", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151111-080003517", "type": "article", "title": "The Apollo 15 Lunar Samples: A Preliminary Description", "author": [ { "family_name": "Gast", "given_name": "P. W.", "clpid": "Gast-PW" }, { "family_name": "Phinney", "given_name": "W. C.", "clpid": "Phinney-W-C" }, { "family_name": "Duke", "given_name": "M. B.", "clpid": "Duke-M-B" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "Samples returned from the Apollo 15 site consist of mare basalts and breccias with a variety of premare igneous rocks. The mare basalts are from at least two different lava flows. The bulk chemical compositions and textures of these rocks confirm the previous conclusion that the lunar maria consist of a series of extrusive volcanic rocks that are rich in iron and poor in sodium. The breccias contain abundant clasts of anorthositic fragments along with clasts of basaltic rocks much richer in plagioclase than the mare basalts. These two rock types also occur as common components in soil samples from this site. The rocks and soils from both the front and mare region exhibit a variety of shock characteristics that can best be ascribed to ray material from the craters Aristillus or Autolycus.", "doi": "10.1126/science.175.4020.363", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1972-01-28", "series_number": "4020", "volume": "175", "issue": "4020", "pages": "363-375" }, { "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:9vte8-rvy24", "collection": "authors", "collection_id": "9vte8-rvy24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151022-084358082", "type": "article", "title": "Observaciones geochronologicas sobre los complejos cristalinos de Sonora y Oaxaca, Mexico", "author": [ { "family_name": "Anderson", "given_name": "Thomas H.", "clpid": "Anderson-T-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "C\u00f3rdoba", "given_name": "Diego A.", "clpid": "C\u00f3rdoba-D-A" }, { "family_name": "Pearson", "given_name": "Mar\u00eda", "clpid": "Pearson-M" }, { "family_name": "Baenteli", "given_name": "Geraldine", "clpid": "Baenteli-G" } ], "abstract": "Reconnaissance geologic mapping and careful study of lead-uranium isotope relationships in zircons from crystalline rocks have resulted in the identification of Precambrian basement from the Mexico-U. S. border, southeast to the known localities near Caborca and from there to Rt. 15 north of Hermosillo. Recent studies have corroborated the presence of Precambrian in Oaxaca. No Precambrian has been identified between Sonora and Oaxaca, but almost no work has been done in these intervening areas.", "issn": "0188-2686", "publisher": "Sociedad Geol\u00f3gica Mexicana", "publication": "Memoria - Sociedad Geologica Mexicana", "publication_date": "1972", "pages": "115-122" }, { "id": "authors:wz2xg-99x69", "collection": "authors", "collection_id": "wz2xg-99x69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140812-151015768", "type": "article", "title": "Preliminary seismological and geological studies of the San Fernando, California, earthquake of February 9 1971", "author": [ { "family_name": "Abrams", "given_name": "M.", "clpid": "Abrams-M" }, { "family_name": "Allen", "given_name": "C.", "clpid": "Allen-C-R" }, { "family_name": "Anderson", "given_name": "D.", "clpid": "Anderson-D-L" }, { "family_name": "Berkey", "given_name": "N.", "clpid": "Berkey-N" }, { "family_name": "Carey", "given_name": "D.", "clpid": "Carey-D" }, { "family_name": "Carter", "given_name": "B.", "clpid": "Carter-B" }, { "family_name": "Davies", "given_name": "G.", "clpid": "Davies-G" }, { "family_name": "Engen", "given_name": "G.", "clpid": "Engen-G-R" }, { "family_name": "Foley", "given_name": "M.", "clpid": "Foley-M-G" }, { "family_name": "Hanks", "given_name": "T.", "clpid": "Hanks-T-C" }, { "family_name": "Helmberger", "given_name": "D.", "clpid": "Helmberger-D-V" }, { "family_name": "Hileman", "given_name": "J.", "clpid": "Hileman-J-A" }, { "family_name": "Jordan", "given_name": "T.", "clpid": "Jordan-T" }, { "family_name": "Jungels", "given_name": "P.", "clpid": "Jungels-P" }, { "family_name": "Kamb", "given_name": "B.", "clpid": "Kamb-B" }, { "family_name": "Liu", "given_name": "H.", "clpid": "Liu-H" }, { "family_name": "Minster", "given_name": "B.", "clpid": "Minster-B" }, { "family_name": "Nordquist", "given_name": "J.", "clpid": "Nordquist-J-M" }, { "family_name": "Penrose", "given_name": "B.", "clpid": "Penrose-B" }, { "family_name": "Silver", "given_name": "L.", "clpid": "Silver-L-T" }, { "family_name": "Smith", "given_name": "R.", "clpid": "Smith-R" }, { "family_name": "Thatcher", "given_name": "W.", "clpid": "Thatcher-W" }, { "family_name": "Thomsen", "given_name": "L.", "clpid": "Thomsen-L" }, { "family_name": "Whitcomb", "given_name": "J.", "clpid": "Whitcomb-J-H" }, { "family_name": "Wood", "given_name": "S.", "clpid": "Wood-S" }, { "literal": "Caltech Division of Geological and Planetary Sciences" } ], "abstract": "The San Fernando earthquake was the largest earthquake to occur in the metropolitan Los\nAngeles area in more than 50 years. It has tentatively been assigned a magnitude, M_L of 6.6, a focal\ndepth of 13.0 km, and an epicentral location about 12 km east of Newhall, California, at 34\u00b024.0'N,\n118\u00b023.7'W (Figure 1), but these figures undoubtedly will be modified as further data become available.\nAlthough the focal depth is not as well defined as the epicenter, it is consistent with other\nobservations suggesting thrusting on a fault plane dipping north about 45 \u00b0 and breaking the surface\nin the Sylmar-San Fernando area (Figure 1). It should be emphasized that the hypocenter of\nthe main shock represents only the point of initial rupture. Breaking, presumably, then propagated\nsouthward and upward from this point, so that the main geological and engineering effects\nwere observed farther south where the fault was shallower and the displacement greater. The location\nof the main shock is based on readings from permanent stations of the Caltech network, as\nwell as the U. S. Geological Survey station at Point Mugu (SBLG) and the California Department\nof Water Resources stations at Pyramid (PYR) and Cedar Springs (CSP). Portable Caltech seismographs\nwere installed in the epicentral area as early as 3 hr following the main shock, and,\nwithin a few days, there were at least 30 portable units in the region operated by various groups\nand agencies.", "issn": "0037-1106", "publisher": "Seismological Society of America", "publication": "Bulletin of the Seismological Society of America", "publication_date": "1971-04", "series_number": "2", "volume": "61", "issue": "2", "pages": "491-495" }, { "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:8rj4j-a4385", "collection": "authors", "collection_id": "8rj4j-a4385", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220728-152248486", "type": "monograph", "title": "Revision of Precambrian stratigraphy in the Prescott-Jerome area, Yavapai County, Arizona", "author": [ { "family_name": "Anderson", "given_name": "C. A.", "clpid": "Anderson-Charles-Alfred" }, { "family_name": "Blacet", "given_name": "P. M.", "clpid": "Blacet-P-M" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Stern", "given_name": "T. W.", "clpid": "Stern-T-W" } ], "abstract": "The metamorphosed volcanic, volcaniclastic, and sedimentary rocks that predate the oldest plutonic rocks in the Prescott-Jerome area (1,770\u00b110 m.y.) are placed in the Yavapai Series, a provincial time-stratigraphic term denned as the 'time interval from 1,770\u00b110 to 1,820+m.y. Two rock-stratigraphic groups are recognized; the Ash Creek Group is1 separated from the Big Bug Group by a major fault and a large pluton of quartz diorite. Isotopic dating now indicates that the Ash Creek Group is older. The name Big Bug Group replaces the term Alder Group, used in earlier publications on the Prescott-Jerome area. \n\nWithin the Big Bug Group the Indian Hills' Volcanics and Green Gulch Volcanites have been shown to be the same formation, and the latter term is retained. Where first described the Chaparral Volcanics was bounded by faults, but subsequent mapping has demonstrated that it occupies the upper part of the Spud Mountain Volcanics; so the term Chaparral Volcanics is abandoned. The Texas Gulch Formation is removed from the Yavapai Series because it is separated from the rocks of the Big Bug Group by a period of plutonism, represented by the Brady Butte Granodiorite, and subsequent erosion.", "doi": "10.3133/b1324C", "publisher": "United States Geological Survey", "publication_date": "1971" }, { "id": "authors:4hmq6-xbm38", "collection": "authors", "collection_id": "4hmq6-xbm38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151022-112739977", "type": "article", "title": "Compositional relations in minerals from kimberlite and related rocks in the Moses Rock dike, San Juan County, Utah", "author": [ { "family_name": "McGetchin", "given_name": "Thomas R.", "clpid": "McGetchin-T-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The Moses Rock dike, a well-exposed, kimberlite-bearing breccia intrusion, crops out in gently dipping beds of the Permian Cutler Formation, in eastern Monument Valley, Utah. \n\nPetrographic, bulk chemical, and electron microprobe analyses of kimberlite and its constituent minerals reveal this highly serpentinized microbreccia contains a primary mineral assemblage consisting of olivine (Mg/Mg+ Fe), 87 to 93), orthopyroxene and clinopyroxene (falling into two compositional ranges after correction for Na-pyroxene molecules-one with Al_2O_3 between 0.5 and 1 percent another, 2 to 5 percent), spinel, chrome-rich pyrope garnet, ilmenite-geikielite, titanoclinohumite and one or more micas. Diamonds are not known. \n\nWe conclude (1) mineral grains in kimberlite are unlike associated dense rock fragments, except rare lherzolite: (2) kimberlite was emplaced as discrete angular mineral clasts, not a silicate melt; (3) P-T assignments based on clinopyroxenes compositions suggest derivation over a depth range in the upper mantle extending to 150 km or more, at temperatures near or below the experimentally determined garnet-lherzolite solidus: (4) the kimberlite was derived by physical disaggregation of both Al-poor and Al-rich pyroxene bearing peridotite in the mantle (garnet- and spinel-lherzolite, respectively); (5) titanoclinohumite is present in both assemblages and may be an important mineralogical site for volatiles in the upper mantle: (6) dense rock fragments (except lherzolite) are unrelated to the kimberlite and are chunks of the vent wall from the crust and possibly the upper mantle sampled during the eruption.", "issn": "0003-004X", "publisher": "Mineralogical Society of America", "publication": "American Mineralogist", "publication_date": "1970-09", "series_number": "9-10", "volume": "55", "issue": "9-10", "pages": "1738-1771" }, { "id": "authors:cekvw-jgn98", "collection": "authors", "collection_id": "cekvw-jgn98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150217-155839306", "type": "article", "title": "Uranium-Thorium-Lead Isotope Relations in Lunar Materials", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The lead isotopic compositions and uranium, thorium, and lead concentrations have been measured on six samples of material from the Sea of Tranquillity. The leads are moderately to very radiogenic; the initial lead concentrations are very low; the uranium and thorium levels are 0.26 to 0.88 and 0.87 to 3.35 parts per million, respectively. The Th/U ratios cluster about a 3.6 value. Apparent ages calculated for four rocks are 4.1 to 4.2 x 10^9 years. Dust and breccia yield apparent ages of 4.60 to 4.63 x 10^9 years. The uranium-lead ages are concordant, or nearly so, in all cases. The lunar surface is an ancient region with an extended record of events in the early history of the solar system. The discrepancy between the rock ages and dust ages poses a fundamental question about rock genesis on the moon.", "doi": "10.1126/science.167.3918.468", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1970-01-30", "series_number": "3918", "volume": "167", "issue": "3918", "pages": "468-471" }, { "id": "authors:b1x6x-rk259", "collection": "authors", "collection_id": "b1x6x-rk259", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141111-141125063", "type": "article", "title": "Titanoclinohumite: A possible mineralogical site for water in the upper mantle", "author": [ { "family_name": "McGetchin", "given_name": "T. R.", "clpid": "McGetchin-T-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Chodos", "given_name": "A. A.", "clpid": "Chodos-A-A" } ], "abstract": "Titanium-rich clinohumite and layered structure minerals are observed in kimberlite and as inclusions in pyropic garnets from the Moses Rock dike, a kimberlite-bearing breccia dike in San Juan County, Utah. Associated clinopyroxenes observed as inclusions within similar pyropes and also in kimberlite are estimated to have equilibrated at depths ranging from about 50 to 150 km at modest temperatures, generally less than 1000\u00b0C. The presence of titanoclinohumite, a high-density hydrous phase, is of considerable interest as a possible site for volatiles in the earth's upper mantle. The dehydration of hydrous phases such as titanoclinohumite within the upper mantle (1) may provide water as a free phase, (2) could be important in the genesis of kimberlite and alkali-basalt magma, and (3) may be one means of producing a low-velocity zone in the upper mantle.", "doi": "10.1029/JB075i002p00255", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1970-01-10", "series_number": "2", "volume": "75", "issue": "2", "pages": "255-259" }, { "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:5zrsj-j9v13", "collection": "authors", "collection_id": "5zrsj-j9v13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151029-074635750", "type": "article", "title": "Pre-Cretaceous basement rocks and their bearing on large-scale displacements in the San Andreas fault system", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Investigations of the history of the pre-Cretaceous crystalline rocks of the Transverse Ranges have indicated a complex history from Permo-Triassic times back to 1700 million years or more. Some of the major historical elements are known to be shared with much larger regions in the southwest; others appear unique to the area, at this time. The close juxtaposition to each other and to the San Andreas fault zone of diverse plutonic and metamorphic rocks of widely different ages provides important possibilities for contributing to the nature and history of displacement on the zone. The most effective evaluation will be possible when the crystalline rocks close to the San Andreas fault can be correctly placed into the regional \"basement\" patterns and history. Unfortunately, the necessary field and laboratory investigations are proceeding very slowly.", "issn": "0081-4350", "publisher": "Stanford University", "publication": "Stanford University Publications. Geological Sciences", "publication_date": "1968", "volume": "11", "pages": "279-280" }, { "id": "authors:y7e10-1z039", "collection": "authors", "collection_id": "y7e10-1z039", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151022-082640004", "type": "article", "title": "A geochronologic investigation of the anorthosite complex, Adirondack mountains, New York", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Cogenetic uranium-lead isotope systems in zircons have been analyzed for five rock samples from the anorthositic domes of the Adirondack highlands and compared with data from a cogenetic suite in a charnockitic gneiss from the Ticonderoga dome in the eastern Adirondacks. Textural and structural arguments applied to the zircons and rocks from the anorthosite suite indicate that some of the zircon are metamorphic and reveal that conditions producing granulite facies metamorphism exited in different parts of the anorthosite complex at discretely different times during the interval from 1020 to 1100 m.y. ago. The Ticonderoga gneiss sample yields an interpreted zircon age of 1130 \u00b1 10 m.y. Zircon characteristics argue this to be the age of magmatic crystallization of the host rock. Extensive studies have confirmed this age as the prevailing age in many large bodies of charnockite (or syenite) gneiss which are peripheral to the anorthosite domes. Petrological arguments\nof persistent spatial association and compositional gradation between the anort11osite and a suite ranging from norite to mangerite, syenite, quartz syenite and granite, imply that all of these rock are comagmatic; this leads to\nthe conclusion that the age of the anorthosite itself is 1130 m.y. No evidence has been found for any older ages in any of the Adirondack orthogneisses to support the hypothesis of a pre-\"Grenville\" basement. The mounting evidence for almost precise age contemporaneity between the Adirondack anorthosite-syenite complex and the Duluth anorthositic gabbro-granophyre complex should provoke a close comparative petrologic and structural scrutiny of these two great stratiform masses.", "issn": "0548-8265", "publisher": "New York State Museum", "publication": "Memoir - New York State Museum and Science Service", "publication_date": "1968", "pages": "233-251" }, { "id": "authors:10802-4h432", "collection": "authors", "collection_id": "10802-4h432", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-104842616", "type": "article", "title": "Petrology of eucrites, howardites and mesosiderites", "author": [ { "family_name": "Duke", "given_name": "Michael B.", "clpid": "Duke-M-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The eucrite and howardite calcium-rich achondrites and many mesosiderites are considered as a coherent meteorite assemblage, their silicates consisting essentially of calciumpoor monoclinic and orthorhombic pyroxenes and calcium-rich plagioclase feldspar. The achondrites can be grouped according to their brecciated structure as follows: eucrites\u2014unbrecciated and monomict brecciated achondrites; howardites\u2014polymict brecciated achondrites. Many mesosiderites contain brecciated structures; they are distinguished from the achondrites by their large metallic fraction. The structure and composition of rock fragments in the breccias indicate a complicated sequence of events including magmatic differentiation, brecciation, recrystallization and refragmentation, and ejection from the parent body. Detailed mineralogical and chemical data suggest that the magmatic differentiation proceeded primarily by the separation of pyroxene from an ultrabasic parent material that had a much lower alkali content than ordinary chondrites. Magmatic crystallization took place in environments ranging from extrusive to deep-seated intrusive. Polymict breccias contain fragments with a wide variety of magmatic and recrystallization textures, which suggests that the breccias were formed either in very large or repeated fragmentation events. Monomict breccias contain fragments with a small range of similar magmatic textures, which suggests that these breccias were formed by small or single events. Petrographic evidence suggests that many of the breccias are impact breccias. Either in their original magmatic crystallization sites or in the sites of breccia accumulation, most of these meteorites apparently had a near-surface location prior to ejection from the parent body.\n\nEvidence obtained from eucrites, howardites and mesosiderites forms an important part of our understanding of the early evolution of the surface regions of their parent body. Chemical and oxidation conditions were different from those presently found in the Earth's crust and upper mantle, but the necessary conditions may have been present in the early history of the Earth. A lunar origin for eucrites, howardites and mesosiderites is proposed, but an asteroidal origin can not be presently excluded.", "doi": "10.1016/0016-7037(67)90112-3", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1967-10", "series_number": "10", "volume": "31", "issue": "10", "pages": "1637-1665" }, { "id": "authors:c2w0n-9c540", "collection": "authors", "collection_id": "c2w0n-9c540", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-101038760", "type": "article", "title": "Uranium and Lead Isotopic Stability in a Metamict Zircon under Experimental Hydrothermal Conditions", "author": [ { "family_name": "Pidgeon", "given_name": "R. T.", "clpid": "Pidgeon-R-T" }, { "family_name": "O'Neil", "given_name": "J. R.", "clpid": "O'Neil-J-R" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" } ], "abstract": "Disturbance of the uranium-lead isotopic system in a metamict Ceylon zircon has been produced in a 2 molal NaCI solution at 500\u00b0C and 1000 bars fluid pressure. Loss of radiogenic lead to the extent of 61 percent in 13 days was the most significant effect. The experimental results support the episodic rather than continuous lead-loss interpretation of natural zircon systems utilized in geochronology.", "doi": "10.1126/science.154.3756.1538", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1966-12-23", "series_number": "3756", "volume": "154", "issue": "3756", "pages": "1538-1540" }, { "id": "authors:vy92p-fjb78", "collection": "authors", "collection_id": "vy92p-fjb78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141111-142013966", "type": "article", "title": "Evaluation of the decay constant of uranium 235 from lead isotope ratios", "author": [ { "family_name": "Banks", "given_name": "Philip O.", "clpid": "Banks-P-O" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The decay constant of U^(235) has been evaluated from the radiogenic Pb^(207)/Pb^(206) ratios of several cogenetic fractions of zircon and uranothorite, analyzed by conventional mass spectrometric methods. Variation of the Pb^(206)/U^(238) apparent ages among the mineral fractions demonstrates that some form of isotopic disturbance has occurred during their geologic history. Arguments are presented to show that the method of calculating \u03bb_(235) is relatively insensitive to such disturbance because of the young geologic age of the samples and the probability that zircon and uranothorite experience isotopic disturbance by partial loss of Pb. Inaccuracy in the calculated value is further reduced by deducing, from geologic and isotopic considerations, the most likely limits to the apparent ages to which the Pb^(207)/Pb^(206) ratios should correspond. Although the uncertainties in the method do not permit a unique derivation of the decay constant, the results suggest that the currently accepted value is probably accurate to within 1%, relative to the accepted values for the decay constant of U^(238) and the isotopic composition of natural U.", "doi": "10.1029/JZ071i016p04037", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1966-08-15", "series_number": "16", "volume": "71", "issue": "16", "pages": "4037-4046" }, { "id": "authors:tnknb-gqj76", "collection": "authors", "collection_id": "tnknb-gqj76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151021-100249965", "type": "article", "title": "Oxygen isotope studies of minerals in stony meteorites", "author": [ { "family_name": "Taylor", "given_name": "Hugh P., Jr.", "clpid": "Taylor-H-P-Jr" }, { "family_name": "Duke", "given_name": "Michael B.", "clpid": "Duke-M-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "abstract": "Oxygen isotope analyses demonstrate the following sequence (as in terrestrial igneous rocks) of increasing O^(18) content for coexisting minerals of stony meteorites: olivine, pyroxene, plagioclase, free silica. Except for the carbonaceous chondrites, the O^(18)/O^(16) ratio of a given mineral is quite uniform in each meteorite class. Differences exist between classes of meteorites, however, as well as between certain meteorites and terrestrial igneous rocks. For example, the O^(18)/O^(16) ratios of meteoritic pyroxenes vary from \u03b4 = \u22120.5 per mil to \u03b4 = + 8.6 per mil (relative to SMOW), whereas pyroxenes in 8 terrestrial igneous rocks have \u03b4-values which range only from + 5.5 to +6.6. The oxygen isotope data suggest a separation of the stony meteorites into three groups, as follows:\n1.\nI. Basaltic achondrites, hypersthene achondrites, and mesosiderites\u2014with pyroxene \u03b4-values of 3.7 to 4.4.\n2.\nII. Hypersthene-olivine chondrites, bronzite-olivine chondrites, enstatite chondrites, enstatite achondrites, and nakhlites\u2014with pyroxene \u03b4-values of 5.3 to 6.3.\n3.\nIII. Types I, II and III carbonaceous chondrites, and ureilites\u2014with highly variable olivine and pyroxene \u03b4-values.\nIt is suggested that the meteorites within each of these three groups are genetically related to one another, but that the three groups may themselves be only distantly related or unrelated. The chondrites have O^(18)/O^(16) ratios similar to their terrestrial analogs, the ultramafic rocks. However, whereas terrestrial basaltic rocks are 1 to 2 per mil richer in O^(18) than ultramafic rocks, the basaltic meteorites are 0.5 to 1.5 per mil lower than chondrites; thus there are serious restrictions placed on any postulated derivation of the basaltic meteorites from chondrites. In addition, the carbonaceous chondrites cannot be simply normal chondrites which have suffered a low-temperature alteration. The olivine in carbonaceous meteorites is lower in O^(18)/O^(16) and isotopically much more variable than chondrite olivine, implying that it is derived from a distinctly different source material.", "doi": "10.1016/0016-7037(65)90043-8", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1965-05", "series_number": "5", "volume": "29", "issue": "5", "pages": "489-512" }, { "id": "authors:qk6v9-zrr53", "collection": "authors", "collection_id": "qk6v9-zrr53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140801-125831579", "type": "article", "title": "Re-examination of isotopic relationships in Colorado Front Range uranium ores", "author": [ { "family_name": "Banks", "given_name": "P. O.", "clpid": "Banks-P-O" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "Some new isotopic analyses of Front Range pitchblende samples and comparisons with published data indicate a complex history of isotopic disturbance in these ores. Relationships in the U^(238)-Pb^(206) and U^(235)-Pb^(207) systems indicate extensive and protracted mobilizations of parents and daughters, and particularly intermediate daughters, in both isotopic series. These relationships preclude a simple, much less unique interpretation of the absolute age of the uranium mineralization in the Front Range. Considering the lack of close definition in the stratigraphic age assignment for this mineralization, it is suggested that the common use of the inferred age in the construction of geologic time scales is not justified.", "doi": "10.1130/0016-7606(1964)75[469:ROIRIC]2.0.CO;2", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "1964-05", "series_number": "5", "volume": "75", "issue": "5", "pages": "469-476" }, { "id": "authors:8ra4s-jzn62", "collection": "authors", "collection_id": "8ra4s-jzn62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220801-90018200", "type": "monograph", "title": "Geology and ore deposits of the Dragoon quadrangle, Cochise County, Arizona", "author": [ { "family_name": "Cooper", "given_name": "John R.", "clpid": "Cooper-John-Roberts" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "The area described in this report is in Cochise County in southeastern Arizona and comprises a little more than 250 square miles in the northwestern part of the county. The mining district known as Johnson Camp is near the center of the area, and the village of Dragoon on the Southern Pacific Railroad is near the southeastern corner. \n\nThe area is in the Mexican Highland section of the Basin and Range province and straddles the divide between the San Pedro valley on the west and the Sulphur Spring valley on the east. \n\nThe Little Dragoon Mountains in the south-central part of the area constitute the principal topographic feature. In the eastern part are the north tip of the Dragoon Mountains, the Gunnison Hills, the Steele Hills, and the south tip of the Winchester Mountains. In the west-central part are the Johnny Lyon Hills, from which a ridge extends northward and joins the Galiuro Mountains north of the area described. \n\nThe rock formations of the area range in age from Precambrian to Recent. The oldest rocks are moderately metamorphosed graywackcs, slates, and lava flows that make up the Pinal schist of early Precambrian age. Also early Precambrian are rhyolite porphyry intrusive sheets and stocks, a large granodiorite mass in the Johnny Lyon Hills, and granite exposed at the south end of the Winchester Mountains. The Tungsten King granite and associated aplite on the west side of the Little Dragoon Mountains, and granite exposed at the north end of the Dragoon Mountains are also referred to the early Precambrian but could be younger. \n\nUpper Precambrian rocks, generally unmetamorphosed, include the Scanlan conglomerate, Pioneer shale, Barnes conglomerate, and Dripping Spring quartzite which are part of the Apache group; extensive diabase sills of Precambrian age were intruded into these rocks.", "doi": "10.3133/pp416", "publisher": "United States Geological Survey", "publication_date": "1964" }, { "id": "authors:jj2yy-qvx96", "collection": "authors", "collection_id": "jj2yy-qvx96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190924-083419112", "type": "article", "title": "Lower Cretaceous Pre-Batholithic Rocks of Northern Baja California, Mexico", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Stehli", "given_name": "F. G.", "clpid": "Stehli-F-G" }, { "family_name": "Allen", "given_name": "C. R.", "clpid": "Allen-C-R" } ], "abstract": "Cretaceous fossils have been found at scattered localities in the pre-batholithic metamorphic rocks of northern Baja California by investigators during the past half-century. The resulting information has been inadequate, however, for the explanation of regional stratigraphic and structural relations, particularly those correlations between the less metamorphosed coastal sections and the more deformed rocks of the mountainous interior.", "issn": "0149-1423", "publisher": "American Association of Petroleum Geologists", "publication": "AAPG Bulletin", "publication_date": "1963-12", "series_number": "12", "volume": "47", "issue": "12", "pages": "2054-2059" }, { "id": "authors:c1y57-3g587", "collection": "authors", "collection_id": "c1y57-3g587", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151022-075922766", "type": "article", "title": "Uranium-Lead Isotopic Variations in Zircons \u2013 A Case Study", "author": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Deutsch", "given_name": "Sarah", "clpid": "Deutsch-S" } ], "abstract": "Zircons in a single 250-pound block of Precambrian Johnny Lyon granodiorite from the Dragoon Quadrangle in Cochise County, Arizona, have been concentrated with special attention to yield and nature of impurities. Morphology, zoning, color, inclusions, size distribution, radioactivity, refractive indexes, cell dimensions, and other properties have been compared with the isotopic properties in the U-Pb system (and to a less precise degree in the Th-Pb system). It has been observed: (1) Uranothorite impurities, while less than 1 per cent in abundance, contribute much more than 50 per cent of the activity in conventionally prepared concentrates. The presence of uranothorite drastically affects the apparent ages in the zirons. (2) The uranothorite can be satisfactorily removed by an appropriate acid-washing procedure. (3) The uranothorite-free zircon concentrates are not homogeneous and show systematic variations in radioactivity and various isotopic properties as a function of average crystal size. (4) Individual zircons show internal variation in radioactivity and may differ in specific activity from other individuals by as much as an order of magnitude. (5) It is possible to strip outer layers experimentally from an aggregate of zircons to determine variations in composite internal isotopic properties. (6) The family of uranium-lead systems distinguished in the inhomogeneous zircon suite may be utilized to establish patterns of isotopic ratio variations that yield much more useful geochronological information than any single system. (7) All systems in this rock appear to have formed 1,655 million years ago and to have been profoundly disturbed by an event 90 million years ago. There is no evidence of any type of disturbance other than this simple episodic pattern. (8) While the mechanism of disturbance is not directly established, it is evident that radioactivity and radiation damage strongly influence susceptibility of the systems to disturbance. (9) It is possible to offer reasonable explanations for some of the puzzling discrepancies between uranium-lead and thorium-lead ages determined on a single mineral concentrate. (10) Recognition of the existence of families of uranium-lead systems among the variable members of a single mineral species, or in associated mineral species, in a single typical granitic rock provides a powerful tool for investigation of the processes and conditions that have influenced the age-dating systems. (11) The systematic variations in U and Th provide interesting information on the role of some trace elements and accessory minerals in the crystallization history of the rock. (12) The Johnny Lyon granodiorite is the oldest igneous rock dated in Arizona thus far and places a minimum age of 1,655 \u00b1 20 million years on the orogeny called Mazatzal Revolution.", "issn": "0022-1376", "publisher": "University of Chicago Press", "publication": "Journal of Geology", "publication_date": "1963-11", "series_number": "6", "volume": "71", "issue": "6", "pages": "721-758" }, { "id": "authors:j6sfj-z3g54", "collection": "authors", "collection_id": "j6sfj-z3g54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170822-102946036", "type": "article", "title": "Precambrian Age Determinations in the Western San Gabriel Mountains, California", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "McKinney", "given_name": "C. R.", "clpid": "McKinney-C-R" }, { "family_name": "Deutsch", "given_name": "S.", "clpid": "Deutsch-S" }, { "family_name": "Bolinger", "given_name": "J.", "clpid": "Bolinger-J" } ], "abstract": "Isotopic age determinations (U-Th-Pb) on zircons from pegmatite and granophyre dikes in the western San Gabriel Mountains have yielded concordant ages of about 1,200 million years. From structural and petrological relations, this is both a minimum and a probable age for the San Gabriel Mountains anorthosite complex. It is also a minimum age for the Mendenhall gneiss, a retrograded \"charnockitic\" granulite which has been intruded by the anorthosite complex. Several zircon fractions from the gneiss yield consistent but moderately discordant apparent ages as follows: Pb^(206)/U^(238) = 1.295m.y., Pb^(207)/U^(235) = 1.355m.y., Pb^(207)/Pb^(206) = 1.440m.y.\n The Pb^(207)/Pb^(206) age is considered minimal for the zircon and, considering genetic uncertainties, a possible minimum age for the parental rock of the gneiss. These age determinations provide the first compelling evidence of Precambrian rocks on the west coast of North America. Their intimate involvement in the great fault systems of southern California complicates our understanding of the history of this part of the continental crust. It is indicated that a significant point on the Pacific margin of the continent originated more than 1,200 million years ago and has persisted without destructive modification to the present.", "doi": "10.1086/626893", "issn": "0022-1376", "publisher": "University of Chicago Press", "publication": "Journal of Geology", "publication_date": "1963-03", "series_number": "2", "volume": "71", "issue": "2", "pages": "196-214" }, { "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:tdn6g-6y385", "collection": "authors", "collection_id": "tdn6g-6y385", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131211-090759937", "type": "article", "title": "A study of the ages of the Precambrian of Texas", "author": [ { "family_name": "Wasserburg", "given_name": "G. J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Wetherill", "given_name": "G. W.", "clpid": "Wetherill-G-W" }, { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Flawn", "given_name": "P. T.", "clpid": "Flawn-P-T" } ], "abstract": "Age determinations using the Sr^(87)-Rb^(87), Ar^(40)-K^(40), and Pb-U methods were made on samples of muscovite, biotite, amphibole, microcline, and zircon from igneous and metamorphic rocks from the Franklin Mountains, Hueco Mountains, Pump Station Hills, and Carrizo and Van Horn Mountains. In addition ages were determined on a number of basement cores from Texas and New Mexico. The results show that a belt of rocks of varied lithology extending from El Paso to east of the Llano uplift are all of the same age. The general age by the strontium and argon methods is 1000 to 1090 m.y.; and by the lead-uranium method on zircons it is 1150 to 1200 m.y. This event is in the same time band as the 'Grenville' orogeny in Canada and the northeastern United States and possibly should be considered part of the general 'Grenville' episode. All the data now available indicate that the orogenic event at about 1000 to 1200 m.y. is the most widespread and pervasive episode of Precambrian orogeny on the North American continent for which adequate evidence has been presented. At least one and probably two older periods of igneous activity and metamorphism occurring at 1250 and 1400 m.y. are found in the northern regions of the Texas Precambrian basement. No evidence was found for any igneous event between the early Paleozoic and the 1000-m.y. episode.", "doi": "10.1029/JZ067i010p04021", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research", "publication_date": "1962-09", "series_number": "10", "volume": "67", "issue": "10", "pages": "4021-4047" }, { "id": "authors:hcnwr-41p64", "collection": "authors", "collection_id": "hcnwr-41p64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220718-524934900", "type": "article", "title": "Uranium-Lead Method On Zircons", "author": [ { "family_name": "Silver", "given_name": "L. T.", "clpid": "Silver-L-T" }, { "family_name": "Deutsch", "given_name": "Sarah", "clpid": "Deutsch-Sarah" } ], "abstract": "In this paper I report some data obtained by a study of zircons from a single block of granite approximately 1.5 cu. ft. in volume. The purpose of this investigation was to better our understanding of geological, mineralogical, and physical-chemical controls on the behavior of U-Pb equilibria in these systems. Along with such parameters as zircon grain size, zoning, and morphology, my associates and I hoped to couple the study with a fair understanding of the geologic history of this particular granitic mass; this understanding is based upon a five-year field-mapping and laboratory-investigation of the area in which the mass is found.", "doi": "10.1111/j.1749-6632.1961.tb35460.x", "issn": "0077-8923", "publisher": "New York Academy of Sciences", "publication": "Annals of the New York Academy of Sciences", "publication_date": "1961-04", "series_number": "2", "volume": "91", "issue": "2", "pages": "279-283" }, { "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:mr3we-re792", "collection": "authors", "collection_id": "mr3we-re792", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140801-124917356", "type": "article", "title": "Agua Blanca fault -- a major transverse structure of northern Baja California, Mexico", "author": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stehli", "given_name": "Francis G.", "clpid": "Stehli-F-G" } ], "abstract": "Agua Blanca fault is a major right-handed strike-slip fault at least 80 miles in length that cuts transversely across the peninsula of Baja California about 70 miles south of the international border. Its trend is anomalous in being more nearly parallel to the Transverse Ranges of southern California than to the San Andres fault system that elsewhere dominates the tectonic grain of the peninsula. Geographic features delineating the fault trace are, from east to west: Paso San Mat\u00edas, Valle de La Trinidad, Ca\u00f1on de Dolores, Valle de Agua Blanca, Valle de Santo Tom\u00e1s, Bah\u00eda Soledad (south branch of fault), Punta Banda (north branch). Farther west, both branches of the fault control submarine topography, and possibly the fault system is continuous with the northwest-trending San Clemente fault off the southern California coast.\n\nPhysiographic expression of the Agua Blanca fault is remarkably similar to that of the San Andreas. Typical features are Recent scarps, offset streams, shutterridges, fault sags and saddles, side-hill ridges, and fault-controlled valleys. Most of these features are particularly well exhibited in Valle de Agua Blanca, which is designated as the type locality.\n\nRocks cut by the fault are mainly Cretaceous plutonic rocks of the southern California batholith and Lower Cretaceous (Albian) metavolcanic rocks. Along the Pacific Coast, the fault cuts Upper Cretaceous (Maestrichtian) post-batholithic sedimentary rocks that are otherwise surprisingly little deformed as compared to rocks of similar age in most of California.\n\nAgua Blanca fault shows a history of right-lateral displacement throughout its length: Recent stream offsets occur from Valle de La Trinidad nearly to the Pacific Ocean; distinctive Quaternary(?) fan gravels in Valle de Agua Blanca are offset laterally 3 miles from their most likely source area across the fault; in the same area, a fault slice of distinctive antiperthitic granodiorite is best explained by 7 miles of lateral displacement, and a nearby slice of quartz diorite may indicate displacement as great as 14 miles. In general, evidence of both Recent activity and amount of total displacement appear to increase westward. The fault coincides in gross aspect with a broad east-west zone of seismic activity in a region elsewhere characterized by relative quiescence, but no large historical earthquakes can be positively correlated with this fault.\n\nDespite its orientation athwart the regional tectonic grain, Agua Blanca fault does not appear to represent a deep-seated structural feature analogous to those of the Transverse Ranges. Instead, it is probably one of several paths by which the San Andreas fault tends to break around the \"knot\" caused by the great bend of the San Andreas in southern California.", "doi": "10.1130/0016-7606(1960)71[467:ABFMTS]2.0.CO;2", "issn": "0016-7606", "publisher": "Geological Society of America", "publication": "Geological Society of America Bulletin", "publication_date": "1960-04", "series_number": "4", "volume": "71", "issue": "4", "pages": "467-482" }, { "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:swdkn-nbz96", "collection": "authors", "collection_id": "swdkn-nbz96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220812-144834119", "type": "article", "title": "A joint-free sample splitter", "author": [ { "family_name": "McKinney", "given_name": "Charles R.", "clpid": "McKinney-Charles-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "abstract": "A sample splitter based on the Jones riffle design has been devised which incorporates certain features not found in other splitters heretofore available. The splitter was folded from one piece of sheet metal and as such has neither cracks or joints to hold up material nor joining metal such as solder to contaminate the sample. It is possible to form the splitter from such materials as plastic and paper or to line metal chutes with these materials. Several sizes of 16-chute splitters have been made in this laboratory; the smallest being made from 0.015 inch thick pure aluminum, each chute opening being \u00bd inch long and \u215b inch wide. This is a microsplitter comparable to the Otto microsplitter in size. The largest splitter was made from 1/32 inch thick pure aluminum, each chute opening being 3 inches long and \u00bd inch wide. An isometric view of a folded 45-degree splitter is shown in Fig. 1. The term \"45-degree\" refers to the angle between the chute bottom and the horizontal. While 45 degrees is greater than the angle of repose, some hang-up is still experienced and cleaning is required. A 60 degree slope should be much better.", "issn": "0003-004X", "publisher": "Mineralogical Society of America", "publication": "American Mineralogist", "publication_date": "1956-06", "series_number": "5-6", "volume": "41", "issue": "5-6", "pages": "521-523" }, { "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" } ]