Ducea, Mihai N. and Saleeby, Jason B.
(1996)
Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry.
Journal of Geophysical Research B, 101
(B4).
pp. 8229-8244.
ISSN 0148-0227.
doi:10.1029/95JB03452.
https://resolver.caltech.edu/CaltechAUTHORS:20140827-081442910
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Abstract
Xenoliths hosted by Cenozoic volcanic flows and plugs from the Central Sierra Nevada and Eastern Sierra Nevada, Owens Valley, and Inyo Mountains were studied for petrography and thermobarometry. The Central Sierra Nevada suite consists of abundant lower crustal feldspathic granulites, garnet clinopyroxenites, and mantle-derived peridotites and garnet websterites. Mafic crustal assemblages occur down to ∼65–70 km, although below 35–40 km, they are mainly in the eclogite facies. In contrast, the Eastern Sierra Region suites show peridotitic, pyroxenitic, and harzburgitic assemblages at depths of ≥35–40 km. They define an adiabat in PT space (T ∼ 1180–1250°C), suggesting the presence of the asthenospheric upper mantle close to the base of the crust. The ultramafic mantle rocks from the Central Sierra Nevada also define an adiabatic slope in PT space, possibly an artifact of side heating from the east. There is xenolith evidence that the Sierra Nevada lost about half of its original crust on the eastern side of the range. Regardless of the actual mechanism of crustal thinning, the loss of the eclogitic lowermost crust and replacement by peridotite in the eastern Sierra Nevada is a process accompanied by a substantial density decrease (>100 kg/m^3). Overall, if the mechanism of eclogitic lowermost crust removal is viable, there are enough buoyancy sources to explain topographic differences between the Sierra Nevada and the adjacent Basin and Range, assuming isostatic equilibrium.
Item Type: | Article |
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Additional Information: | © 1996 by the American Geophysical Union.
Received June 20, 1995; revised November 2, 1995; accepted November 9, 1995.
Paper number 95JB03452.
This research was supported by the Office of
Basic Energy Sciences at the Department of Energy (DE-FG03-93ER14311). M. Ducea acknowledges a Penrose grant from the Geological
Society of America. Extremely valuable journal reviews were
provided by Calvin Miller, Ronald Kistler, and an anonymous reviewer.
We thank Slawek Tulaczyk, Liz Holt, and Rob Brady for field
Assistance; Paul Carpenter for electron microprobe logistics help; and
Mark Abolins for assistance with Figure 1. The staffs of Sequoia and
Kings Canyon National Parks provided critical support for field work.
The Southern Sierra Continental Dynamics group is acknowledged for
constructive criticism during group meetings. We are particularly
thankful to Peter Malin, chief scientist of the project. We thank Sorena
Sorensen for providing samples of the Dodge collection, currently
stored at the Smithsonian Institution. Earlier versions of this manuscript
were improved by Elizabeth Nagy and Slawek Tulaczyk. California
Institute of Technology Division of Geological and Planetary
Sciences contribution 5550. |
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Funders: | Funding Agency | Grant Number |
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Department of Energy (DOE) | DE-FG03-93ER14311 | Geological Society of America Penrose Bequest Research Grants | UNSPECIFIED |
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Other Numbering System: | Other Numbering System Name | Other Numbering System ID |
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Caltech Division of Geological and Planetary Sciences | 5550 |
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Issue or Number: | B4 |
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DOI: | 10.1029/95JB03452 |
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Record Number: | CaltechAUTHORS:20140827-081442910 |
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Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20140827-081442910 |
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Official Citation: | Ducea, M. N., and J. B. Saleeby (1996), Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry, J. Geophys. Res., 101(B4), 8229–8244, doi:10.1029/95JB03452 |
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Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. |
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ID Code: | 48957 |
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Collection: | CaltechAUTHORS |
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Deposited By: |
Tony Diaz
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Deposited On: | 29 Aug 2014 22:40 |
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Last Modified: | 10 Nov 2021 18:38 |
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