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Structural history of continental volcanic arc rocks, eastern Sierra Nevada, California: A case for extensional tectonics

Tobisch, Othmar T. and Saleeby, Jason B. and Fiske, Richard S. (1986) Structural history of continental volcanic arc rocks, eastern Sierra Nevada, California: A case for extensional tectonics. Tectonics, 5 (1). pp. 65-94. ISSN 0278-7407. doi:10.1029/TC005i001p00065.

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Mesozoic metavolcanic rocks forming part of the continental volcanic arc along the eastern Sierra Nevada near Mt. Goddard and in the Ritter Range show a complex history related to extensional tectonics. The rocks comprise a thick section of tuffs, breccias, lava flows, sills, and ash-flow tuffs deposited in a subaerial to subaqueous environment, with some subvolcanic sill-like plutons. Pb/U ages of the rocks in the Mt, Goddard area range from ca. 130–160 Ma, while rocks in the Ritter Range have a somewhat wider age range as reported previously. Repetition of the section occurs by faulting, and with the exception of parts of the mid-Cretaceous Minarets Caldera, all the volcanic rocks show a regional slaty cleavage which was subsequently crenulated and/or folded locally. The first cleavage has well-developed stretching lineations, and does not appear to have been associated with significant folding. Finite strain measurements show considerable variation both in magnitude and symmetry. The Mt. Goddard rocks, however, tend to show slightly higher overall strain magnitude and greater constrictional component than the Ritter Range for rocks of comparable age. Calculations based on the strain data suggest the Mt. Goddard section has been thinned by about 50% normal to bedding, much as that documented previously for rocks in the Ritter Range. Deformation within this part of the continental arc was originally thought to have formed by regional compression during the late Jurassic (Nevadan) orogeny. However, our study indicates that (1) parts of the deformed volcanic section are younger than late Jurassic, (2) Nevadan-age breaks in deposition are not present, (3) large-scale folds expected during a regional compression event are not common, and (4) the beds were tilted to a high dip prior to internal deformation. An extensional model is proposed in which beds were rotated to high tilts early in the deformation as a result of listric normal faulting. This normal faulting is thought to have occurred above a regional tumescence related to voluminous magmatism at depth, with preservation of the steeply tilted Goddard and Ritter sections being facilitated by their downward transport along the margins of rising plutons. Flattening and steeply plunging constrictional fabrics superimposed on the tilted sections are related to strain induced by high-level inflation of magma chambers and downward return flow of the keellike pendants. The main tectonic fabric shown by the continental volcanic arc rocks in the eastern Sierra Nevada is largely of Cretaceous age, rather than Jurassic (Nevadan) as originally supposed. In addition, the deformation, both rotation of beds and subsequent tectonite fabric, appears to be genetically related to the dynamic evolution of the magmatic arc, and not the result of an externally imposed tectonic event.

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Additional Information:© 1986 by the American Geophysical Union. Received May 8, 1985; revised October 7, 1985; accepted October 8, 1985. Paper number 5T0776. Field and laboratory work has been supported in part by the U.S. Geological Survey, the Fluid Research Fund of the Smithsonian Institution, a Faculty Research Grant from the University of California, Santa Cruz, and N.S.F. grant EAR 8206478 awarded to Tobisch. Geochronological work was supported by N.S.F. grants EAR 8018811 and EAR 8218460 awarded to Saleeby. Patience and expertise in hand purification and sorting of zircon fractions by Cherilyn Saleeby was essential for this study. We are grateful to T. W. Stern of the U.S. Geological Survey for his important contributions in age dating of the Ritter Range rocks, the complete report of which will be published elsewhere. Jack Collender, Steve Davis, arid Joe Frey generously contributed their time and effort to the mapping, data collecting and its analysis from part of the area as shown in Plate 1, inset. We thank Marty Morrison for running electronprobe analyses on andalusite and plagioclase in one specimen. Reviews by Paul Bateman, Frank Dodge, Phil Gans, Ben Page and Rich Schweickert helped clarify our writing, for which we are grateful.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Smithsonian Institution Fluid Research FundUNSPECIFIED
University of California, Santa Cruz, Faculty Research GrantUNSPECIFIED
NSFEAR 8206478
NSFEAR 8018811
NSFEAR 8218460
Issue or Number:1
Record Number:CaltechAUTHORS:20140827-145836050
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Official Citation:Tobisch, O. T., J. B. Saleeby, and R. S. Fiske (1986), Structural history of continental volcanic arc rocks, eastern Sierra Nevada, California: A case for extensional tectonics, Tectonics, 5(1), 65–94, doi:10.1029/TC005i001p00065.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49007
Deposited By: Ruth Sustaita
Deposited On:27 Aug 2014 22:27
Last Modified:10 Nov 2021 18:38

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