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Composite Devonian island-arc batholith in the northern Sierra Nevada, California

Hanson, Richard E. and Saleeby, Jason and Schweickert, Richard A. (1988) Composite Devonian island-arc batholith in the northern Sierra Nevada, California. Geological Society of America Bulletin, 100 (3). pp. 446-457. ISSN 0016-7606. http://resolver.caltech.edu/CaltechAUTHORS:20140825-140529013

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Abstract

The Bowman Lake batholith intrudes the pre-Upper Devonian Shoo Fly Complex in the northern Sierra Nevada. The eastern margin of the batholith extends to within 1.5 km of the base of a thick sequence of Paleozoic island-arc rocks that rests unconformably on the Shoo Fly Complex. Hypabyssal silicic intrusions associated with the batholith penetrate the Upper Devonian Sierra Buttes Formation, the lowest volcanic unit of the arc sequence, but do not extend to higher stratigraphic levels. The intrusions in the Sierra Buttes Formation possess marginal peperites and show other evidence of their injection into wet, unconsolidated sediments. On the basis of these field relations, the batholith is interpreted to represent a subvolcanic magma chamber emplaced concurrently with deposition of Sierra Buttes arc rocks. The batholith is composite and consists of trondhjemite, granodiorite, biotite granite, and hornblende tonalite, formed from discrete batches of magma injected into a common plutonic chamber. Mingling of tonalitic and trondhjemitic magmas produced abundant rounded inclusions of tonalite dispersed within trondhjemite and led to hybridization of the two magmas by fine-scale intermixing. Zircons from the trondhjemitic, granodioritic, and granitic phases of the batholith and an associated Sierra Buttes rhyolite sill show complex U-Pb isotopic systematics. A multistage history is suggested, involving the incorporation of earliest Paleozoic and/or Proterozoic zircons during magma generation or ascent in Devonian time and one or more stages of disturbance in Mesozoic-Cenozoic(?) time. Consideration of these different discordance mechanisms results in a model U-Pb igneous age for the batholith of 364 to 385 Ma (Middle to Late Devonian); on the basis of the field relations, a Late Devonian age for the batholith is adopted. Zircon characteristics and isotopic systematics suggest that petrogenesis of the granite involved mixing of trondhjemitic and/or granodioritic magmas with partial melt from a separate, large-ion-lithophile-enriched source.


Item Type:Article
Related URLs:
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http://dx.doi.org/10.1130/0016-7606(1988)100<0446:CDIABI>2.3.CO;2DOIArticle
http://gsabulletin.gsapubs.org/cgi/doi/10.1130/0016-7606(1988)100%3C0446:CDIABI%3E2.3.CO;2PublisherArticle
http://bulletin.geoscienceworld.org/cgi/doi/10.1130/0016-7606(1988)100%3C0446:CDIABI%3E2.3.CO;2PublisherArticle
Additional Information:© 1988 Geological Society of America. Manuscript received by the Society December 23, 1985; Revised manuscript received August 20, 1987; Manuscript accepted September 9, 1987. Hanson is indebted to G. H. Girty for assistance and numerous discussions, to T. A. Vogel for conversations regarding magma mixing, and to B. Wardlaw for identification of conodonts from the Sierra Buttes Formation. Field work was supported by National Science Foundation Grant EAR 78-14779 to Schweickert. Geochronological work was supported by National Science Foundation Grants EAR 80-18811 and EAR 82-18460 to Saleeby. Patience and expertise in hand purification and sorting of zircon fractions by Cherilyn Saleeby were essential for this study. Fission-track radiographic data were kindly provided by D. S. Burnett. The manuscript benefited greatly from reviews by T. J. Wilson, D. C. Turner, G. A. Davis, J. L. Anderson, and J. E. Wright.
Funders:
Funding AgencyGrant Number
NSFEAR 78-14779
NSFEAR 80-18811
NSFEAR 82-18460
Record Number:CaltechAUTHORS:20140825-140529013
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140825-140529013
Official Citation:RICHARD E. HANSON, JASON B. SALEEBY, and RICHARD A. SCHWEICKERT Composite Devonian island-arc batholith in the northern Sierra Nevada, California Geological Society of America Bulletin, March, 1988, v. 100, p. 446-457, doi:10.1130/0016-7606(1988)100<0446:CDIABI>2.3.CO;2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48858
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Aug 2014 21:15
Last Modified:25 Aug 2014 21:15

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