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U/Pb zircon, strontium, and oxygen isotopic and geochronological study of the southernmost Sierra Nevada Batholith, California

Saleeby, Jason B. and Sams, David B. and Kistler, Ronald W. (1987) U/Pb zircon, strontium, and oxygen isotopic and geochronological study of the southernmost Sierra Nevada Batholith, California. Journal of Geophysical Research B, 92 (B10). pp. 10443-10466. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20140826-124506770

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Abstract

The southernmost Sierra Nevada offers a view into the deep levels of the Mesozoic batholithic belt which constitutes much of the range to the north, and represents one of the major tectonic features of western North America. The main crystalline rocks of the study area are (1) the intrusive suite of Bear Valley, a middle Cretaceous tonalite batholith complex with coeval gabbroic intrusives, and (2) the gneiss complex of the Tehachapi Mountains, which consists of Early Cretaceous orthogneiss and subordinate paragneiss, with local domains having granulite facies metamorphic assemblages. The orthogneisses are dominantly tonalitic in composition, with significant layers of granodioritic to granitic and lesser dioritic to gabbroic gneiss. Quartz-rich and psammitic metasedimentary rocks with subordinate marble constitute the main framework assemblage into which the plutonic rocks were emplaced. Field relations demonstrate assimilation of metasedimentary material into the orthogneiss and tonalite batholith magmas, and magma mixing between mafic, tonalitic, and granitic materials. Significant domains of both homogenization and inhomogenization are recognized isotopically within the mixed rocks. U/Pb zircon studies have resolved two major igneous suites and a third suite of postdeformational intrusives, all lying between 90 and 120 Ma. The first suite (gneiss complex of the Tehachapi Mountains) was emplaced at ∼115 Ma, and exhibits penetrative high-temperature deformation developed at or near solidus conditions. A number of discordance patterns, along with the physical properties of the zircon, suggest minor inheritance of Proterozoic zircon and limited open system behavior in response to a major 100 Ma plutonic event. The 100 ± 3 Ma intrusive suite of Bear Valley crosscuts the older suite, but also exhibits significant synplutonic deformation. Mainly concordant zircon ages indicate the igneous crystallization age, but some discordances occur due to inheritance or entrainment of Proterozoic zircon. The high-temperature deformation fabrics in these suites and within the metasedimentary framework rocks were crosscut by the granodiorite of Claraville (90 Ma) and pegmatite dikes (∼95 Ma). The granodiorite of Claraville shows strong inheritance of Proterozoic zircon and high initial ^(87)Sr/^(86)Sr and δ^(18)O. Zircon populations from paragneiss and quartzite samples are dominated by Proterozoic detrital grains. Strontium and oxygen isotopic data on the zircon geochronology sample suite suggest simple twocomponent mixing of mantle-derived gabbroic to tonalitic magmas with partial to complete melt products from the metasedimentary framework rocks. Sedimentary admixtures for some granitic rocks may be as high as 45%, but for the tonalitic batholithic complex are no higher than about 15%. Modeled values of 10–20% metasediment are typical for the orthogneisses. Initial ^(87)Sr/^(86)Sr correlates directly with δ^(18)O, and generally correlates inversely with Sr content. Some subtle complexities in the Sr and O isotopic data suggest the involvement of a third cryptic component. Such a component could be early Phanerozoic ensimatic accretionary terranes that were structurally beneath the observed metasedimentary sequence, or altered oceanic crust and sediments introduced into the mantle magma source area by subduction. One of the initial aims of this study was to seek out remnants of Proterozoic sialic crystalline rocks within the gneiss complex of the Tehachapi Mountains. No such remnants were found, and our studies strongly suggest that sialic components within this link of the Mesozoic batholithic belt were introduced into mantle-derived magraatic systems by anatexis of continent-derived sedimentary rocks.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/JB092iB10p10443DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/JB092iB10p10443/abstractPublisherArticle
Additional Information:© 1987 by the American Geophysical Union. Received September 12, 1986; revised April 22, 1987; accepted April 30, 1987. Paper number 6B6290. Field and zircon geochronological work was supported by NSF grants EAR 8018811, EAR 8218460, and EAR 8419731 awarded to Saleeby. Fieldwork by Sams was also supported by Geological Society of America Penrose grants. Special thanks to the Tejon Ranch Company for access to much of the study area. Discussions with D.C. Ross, John Sharry, L.T. Silver, A.L. Albee, and H.P. Taylor, Jr., have been very helpful. Reviews by G.L. Farmer, R.J. Fleck, J.M. Mattinson, and J. Wooden were of great assistance. California Institute of Technology Division of Geological and Planetary Sciences contribution 4467.
Funders:
Funding AgencyGrant Number
NSFEAR 8018811
NSFEAR 8218460
NSFEAR 8419731
Geological Society of America Penrose Bequest Research GrantsUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences4467
Issue or Number:B10
Record Number:CaltechAUTHORS:20140826-124506770
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140826-124506770
Official Citation:Saleeby, J. B., D. B. Sams, and R. W. Kistler (1987), U/Pb zircon, strontium, and oxygen isotopic and geochronological study of the southernmost Sierra Nevada Batholith, California, J. Geophys. Res., 92(B10), 10443–10466, doi:10.1029/JB092iB10p10443
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48919
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:26 Aug 2014 20:06
Last Modified:03 Oct 2019 07:08

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