A summary of critical relations in the central part of the Sierra Nevada batholith, California, U.S.A.
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U–Pb geochronologic studies demonstrate that steeply dipping, sheetlike tonalitic plutons along the western margin of the northern Coast Mountains batholith were emplaced between ~83 and ~57 (perhaps ~55) Ma. Less elongate tonalitic–granodioritic bodies in central portions of the batholith yield ages of 59–58 Ma, coeval with younger phases of the tonalitic sheets. Large granite–granodiorite bodies in central and eastern portions of the batholith were emplaced at 51–48 Ma. Trends in ages suggest that the tonalitic bodies generally become younger southeastward and that, at the latitude of Juneau, plutonism migrated northeastward across the batholith at ~0.9 km/Ma. Variations in the age, shape, location, and degree of fabric development among the various plutons indicate that Late Cretaceous – Paleocene tonalitic bodies were emplaced into a steeply dipping, dip-slip shear zone that was active along the western margin of the batholith. Postkinematic Eocene plutons were emplaced at shallow crustal levels. Inherited zircon components in these plutons range in age from mid-Paleozoic to Early Proterozoic and are coeval with detrital zircons in adjacent metasedimentary rocks. These old zircons, combined with evolved Nd isotopic signatures for most plutons, record assimilation of continental crustal or supracrustal rocks during the generation and (or) ascent of the plutons.
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New geological mapping in the centre of the Galway Granite at Camus, Co. Galway, reveals a major north—south thrust zone, the Furnace Thrust, typically dipping east at 35°, which thrust up westward deeper-crystallised granite, including two minor late intrusions, on top of a higher-level granite footwall. Al-in-hornblende geobarometry of the footwall and the hanging wall confirms the thrusting. At 2km east of the thrust, both the footwall and the hanging wall of the thrust sheet were later substantially further uplifted by the steeper Shannawona Fault. At 6km east of this fault, the granite contains post-400—395Ma, pre-370—378Ma thrusts that moved south-eastward, so a major block of the deep ∼400—395Ma Megacrystic Granite has been squeezed upward. This granite still farther east was later uplifted more by the steep Shannapheasteen Fault, which is connected with the late (?380Ma) central intrusion of the Shannapheasteen Granite, which pushed its roof upward. The uplift of the Central Block with its deeply crystallised Megacrystic Granite was therefore the result of thrusts and faults connected in a complex way with the coeval intrusive pressures of the late emplacement of the Shannapheasteen Granite and six other late granites. All seven late granites are confined to the Central Block and, having low densities, exerted protracted buoyancy uplift forces. This modifies the previous partly correct, but mechanically difficult, explanation for the origin of the Central Block of the Galway Batholith.
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Undeformed ash-flow tuffs for which a late Eocene age is herein established unconformably overlie eroded granitic rocks of the largely Cretaceous and Paleocene coastal batholith in the lower part of the Pacific slope of the Andes 60 km east of Lima, Peru. These relations (1) indicate rapid uplift of the coastal region, as well as areas farther inland, shortly after Cretaceous-Paleocene plutonism; (2) provide additional evidence for a pulse of Eocene deformation, igneous activity, and uplift contemporaneous with the change in plate movement reflected by the bend in the Hawaii-Emperor trace; (3) suggest that certain of the centered volcano-plutonic complexes of the coastal batholith may have remained active after uplift and erosion of older rocks of the batholith; and (4) demonstrate that rocks of the coastal region and the lower western slopes of the Andes were largely unaffected by middle Miocene tectonism.
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The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting and folding, and west-northwest stretching. Contraction ended shortly after emplacement, as indicated by high-temperature recrystallization in thrust-related mylonites of the pluton and by geochronological data, whereas west-northwest stretching continued for an unknown period of time. This is the best documented mid-Cretaceous contractional belt in the main part of the crystalline core. The shortening direction and timing are identical to that of southwest-vergent thrusts in the offset continuation of the core in British Columbia. The contractional belt provides a link between thrusting in the Northwest Cascades thrust system and deformation in the crystalline core.
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The southern boundary of the high level, discordant, Devonian Strathbogie batholith in central Victoria includes two near-linear sections that strike east–west, and one north–south. Field mapping has delineated the 100 km southern boundary with 2200 waypoints taken where granite and hornfels are within 10 m of one another. There is 790 m of topographic relief along the southern boundary and, where the mapping is overlain on contours, there are intervals that reflect a steep-dipping contact and others that reflect near-horizontal contacts. Of the latter, some reflect the granite roof and others the floor. Complementary evidence from mineralogic and textural data indicates a strong correlation between the interpreted roof of the granite and the abundance of tourmaline, aplite and pegmatite. When combined, the roof and floor intervals indicate a batholith thickness up to 350 m; nowhere along the southern boundary can a thickness of 1 km be demonstrated. Along the southern boundary, at least, the batholith shape is a thin, tabular and extensive composite granite sheet analogous to a pizza rather than a pipe. The roof of the granite is nearly horizontal in both east–west and north–south sections, and the plateaux today are close to the batholith roof. On regional and local scales, granite emplacement was determined by pre-existing anisotropies, such as master joint sets, across which the propagation of magma-filled fractures (granite sheets) was arrested. The emplacement records a fine balance between magma pressure, and the interplay of lower confining (overburden) pressures and pre-existing anisotropies that also facilitated roof uplift. The opportunistic magmas used the slightest variations of those parameters. This interpretation of the Strathbogie batholith matches examples in the Himalaya and Chilean Andes but differs markedly from the portrayal of very large batholiths beneath Cu–Au porphyry systems.KEY POINTSThe boundary of the Strathbogie batholith can be mapped in moderately outcropping terrain to an accuracy of 10 m or better.Steep intervals of the boundary are interspersed with near-horizontal intervals that delineate the granite floor and roof along the 100 km of the southern boundary.The batholith, at least near its southern boundary, comprises near-horizontal sheets of <500 m aggregate thickness.The boundary determined by geophysics is adequate for regional studies but has been misleading in three-dimensional interpretations.
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Research Article| June 01, 2001 Forearc-basin sedimentary response to rapid Late Cretaceous batholith emplacement in the Peninsular Ranges of southern and Baja California David L. Kimbrough; David L. Kimbrough 1Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA Search for other works by this author on: GSW Google Scholar Douglas P. Smith; Douglas P. Smith 2Earth Systems Science & Policy Institute, California State University Monterey Bay, Seaside, California 93955-8001, USA Search for other works by this author on: GSW Google Scholar J. Brian Mahoney; J. Brian Mahoney 3 Department of Geology, University of Wisconsin, Eau Claire, Wisconsin 54702, USA Search for other works by this author on: GSW Google Scholar Thomas E. Moore; Thomas E. Moore 4U.S. Geological Survey, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Marty Grove; Marty Grove 5Department of Earth & Space Sciences, University of California, Los Angeles, California 90095, USA Search for other works by this author on: GSW Google Scholar R. Gordon Gastil; R. Gordon Gastil 8Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA Search for other works by this author on: GSW Google Scholar Amabel Ortega-Rivera; Amabel Ortega-Rivera 6Instituto de Geologia, Campus Universidad Nacional Autónoma de México–Juriquilla, Querétaro 76000, Mexico Search for other works by this author on: GSW Google Scholar C. Mark Fanning C. Mark Fanning 7Australian National University, Canberra, ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information David L. Kimbrough 1Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA Douglas P. Smith 2Earth Systems Science & Policy Institute, California State University Monterey Bay, Seaside, California 93955-8001, USA J. Brian Mahoney 3 Department of Geology, University of Wisconsin, Eau Claire, Wisconsin 54702, USA Thomas E. Moore 4U.S. Geological Survey, Menlo Park, California 94025, USA Marty Grove 5Department of Earth & Space Sciences, University of California, Los Angeles, California 90095, USA R. Gordon Gastil 8Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA Amabel Ortega-Rivera 6Instituto de Geologia, Campus Universidad Nacional Autónoma de México–Juriquilla, Querétaro 76000, Mexico C. Mark Fanning 7Australian National University, Canberra, ACT 2601, Australia Publisher: Geological Society of America Received: 18 Sep 2000 Revision Received: 22 Jan 2001 Accepted: 12 Feb 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2001) 29 (6): 491–494. https://doi.org/10.1130/0091-7613(2001)029<0491:FBSRTR>2.0.CO;2 Article history Received: 18 Sep 2000 Revision Received: 22 Jan 2001 Accepted: 12 Feb 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David L. Kimbrough, Douglas P. Smith, J. Brian Mahoney, Thomas E. Moore, Marty Grove, R. Gordon Gastil, Amabel Ortega-Rivera, C. Mark Fanning; Forearc-basin sedimentary response to rapid Late Cretaceous batholith emplacement in the Peninsular Ranges of southern and Baja California. Geology 2001;; 29 (6): 491–494. doi: https://doi.org/10.1130/0091-7613(2001)029<0491:FBSRTR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The eastern Peninsular Ranges batholith is dominated by voluminous La Posta–type tonalite-granodiorite intrusions that compose half of the magmatic arc at present erosion level. Zircon U-Pb and hornblende 40Ar/39Ar results from these intrusions indicate that they were emplaced in a remarkably narrow interval (99–92 Ma) that closely followed cessation of west-directed compression of the arc system. Emplacement of the La Posta suite coincided with a major pulse of coarse-grained sediment into the adjacent forearc basin in early Cenomanian to middle Turonian time. Paleontologic control, and plutonic age and detrital zircon U-Pb data demonstrate the virtual absence of a time lag between magma emplacement and sedimentary response. The tight linkage between magmatism, arc exhumation, and sediment delivery to the forearc indicates that development of major erosional topography in the arc was driven by thermal and mechanical effects associated with large-volume batholith emplacement. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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