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Isotopic systematics of Pb/U (zircon) and ^(40)Ar/^(39)Ar (biotite-hornblende) from rocks of the central Foothills terrane, Sierra Nevada, California

Saleeby, Jason B. and Geary, Edward E. and Paterson, Scott R. and Tobisch, Othmar T. (1989) Isotopic systematics of Pb/U (zircon) and ^(40)Ar/^(39)Ar (biotite-hornblende) from rocks of the central Foothills terrane, Sierra Nevada, California. Geological Society of America Bulletin, 101 (11). pp. 1481-1492. ISSN 0016-7606. http://resolver.caltech.edu/CaltechAUTHORS:20140825-102310759

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Abstract

Pb/U zircon and ^(40)Ar/^(39)Ar biotite-horn-blende studies in conjunction with detailed structural and textural studies clarify the age and structural relations of a unique cluster of plutons in the central Sierra Nevada western metamorphic belt. The plutons range from gabbro to tonalite/trondhjemite and include the Guadalupe Igneous Complex. Magmatic emplacement ages for the plutons are for the most part between ∼150 and ∼145 m.y., as recorded in both the zircon and hornblende isotopic systems. Additional ages of 138 and 123 m.y. were determined on small plutons having key structural settings. In general, the Pb/U and ^(40)Ar/^(39)Ar isotopic systems are well behaved. Second-order complications are locally present in the Pb/U systems, owing to the entrainment of older zircon from wall rocks, and in ^(40)Ar/^(39)Ar systems, owing to minor compositional differences in mica and amphibole phases. The age data and structural relations of the plutons in conjunction with ^(40)Ar/^(39)Ar metamorphic wall-rock biotite and hornblende age data constrain regional ductile deformation in the study area to have occurred between ∼150 and ∼125 Ma. Such deformation was accompanied by upper greenschist- to lower amphibolite-facies metamorphism and is at least in part closely related to pluton emplacement. Such deformation and metamorphism has in the past been attributed to the Late Jurassic Nevadan orogeny. This study shows clearly, however, that ductile deformation and metamorphism in the study area are post-Nevadan if modern concepts of the Nevadan orogeny are strictly adopted.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1130/0016-7606(1989)101<1481:ISOPUZ>2.3.CO;2DOIArticle
http://gsabulletin.gsapubs.org/content/101/11/1481PublisherArticle
http://bulletin.geoscienceworld.org/content/101/11/1481PublisherArticle
Alternate Title:Isotopic systematics of Pb/U (zircon) and 40Ar/39Ar (biotite-hornblende) from rocks of the central Foothills terrane, Sierra Nevada, California
Additional Information:© 1989 Geological Society of America. Manuscript received by the Society August 22, 1988; Revised manuscript received February 28, 1989; Manuscript accepted March 6, 1989. This research was supported by National Science Foundation (NSF) Grants EAR84-07788 and AEO84-15114 and the Weingart Foundation to Saleeby and NSF Grants EAR83-18212 and EAR86-07017 to Tobisch. We thank T. M. Harrison and M. Heizler for permission to use the argon isotope facilities at the State University of New York at Albany and for their helpful comments on the manuscript. We also thank Mike Wolf for his assistance in the collecting and mineral separation of the Guadalupe Igneous Complex, and Cherilyn Saleeby for patience and expertise in hand sorting of zircon. Reviews from J. M. Mattinson, R. A. Schweickert, and W. D. Sharp were helpful.
Funders:
Funding AgencyGrant Number
NSFEAR84-07788
NSFAEO84-15114
Weingart FoundationUNSPECIFIED
NSFEAR83-18212
NSFEAR86-07017
Record Number:CaltechAUTHORS:20140825-102310759
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140825-102310759
Official Citation:JASON B. SALEEBY, EDWARD E. GEARY, SCOTT R. PATERSON, and OTHMAR T. TOBISCH Isotopic systematics of Pb/U (zircon) and 40Ar/39Ar (biotite-hornblende) from rocks of the central Foothills terrane, Sierra Nevada, California Geological Society of America Bulletin, November, 1989, v. 101, p. 1481-1492, doi:10.1130/0016-7606(1989)101<1481:ISOPUZ>2.3.CO;2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48843
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Aug 2014 19:19
Last Modified:25 Aug 2014 19:19

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