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GEOREF RECORD

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

Jason B. Saleeby, Edward E. Geary, Scott R. Paterson and Othmar T. Tobisch
Isotopic systematics of Pb/U (zircon) and (super 40) Ar/ (super 39) Ar (biotite-hornblende) from rocks of the central Foothills Terrane, Sierra Nevada, California
Geological Society of America Bulletin (November 1989) 101 (11): 1481-1492

Abstract

Pb/U zircon and (super 40) Ar/ (super 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 approximately 150 and approximately 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 (super 40) Ar/ (super 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 (super 40) Ar/ (super 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 (super 40) Ar/ (super 39) Ar metamorphic wall-rock biotite and hornblende age data constrain regional ductile deformation in the study area to have occurred between approximately 150 and approximately 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.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 101
Serial Issue: 11
Title: Isotopic systematics of Pb/U (zircon) and (super 40) Ar/ (super 39) Ar (biotite-hornblende) from rocks of the central Foothills Terrane, Sierra Nevada, California
Affiliation: Calif. Inst. Technol., Div. Geol. and Planet. Sci., Pasadena, CA, United States
Pages: 1481-1492
Published: 198911
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 47
Accession Number: 1989-074837
Categories: GeochronologyIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N37°19'60" - N37°40'00", W120°30'00" - W120°00'00"
Secondary Affiliation: San Jose State Univ., USA, United StatesUniv. Calif., USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1989
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