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Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

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. http://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.


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http://dx.doi.org/10.1029/95JB03452DOIArticle
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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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Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-93ER14311
Geological Society of America Penrose Bequest Research GrantsUNSPECIFIED
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Caltech Division of Geological and Planetary Sciences5550
Record Number:CaltechAUTHORS:20140827-081442910
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140827-081442910
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
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48957
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:29 Aug 2014 22:40
Last Modified:29 Aug 2014 22:40

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