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Seismic evidence for orthopyroxene enrichment in the continental lithosphere

Wagner, Lara S. and Anderson, Megan L. and Jackson, Jennifer M. and Beck, Susan L. and Zandt, George (2008) Seismic evidence for orthopyroxene enrichment in the continental lithosphere. Geology, 36 (12). pp. 935-938. ISSN 0091-7613.

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We assess the ability of predicted seismic velocities (Vp, compressional wave; Vs, shear wave; and Vp/Vs) to identify regions in the upper mantle that are enriched in orthopyroxene relative to normal melt-depleted peridotite compositions. Orthopyroxene enrichment has been found in mantle xenoliths from a number of locations, including the Colorado Plateau and the Kaapvaal craton. We find that the Vp/Vs ratio is very sensitive to orthopyroxene concentration, but it is not sensitive to depletion level. We compare these predicted velocities and Vp/Vs ratios to the high Vs, low Vp/Vs anomaly found above the central Chile–Argentina flat slab. Within error, the predicted velocities of some of the orthopyroxene-enriched xenoliths match the observed velocities from the Chile-Argentina upper mantle. Because the anomaly above the central Chile–Argentina flat slab does not conform to known terrane boundaries but does align with the downgoing Juan Fernandez ridge track, we suggest that the orthopyroxene enrichment in this area may be related to flat slab processes, which would have implications for our understanding of lithospheric silica enrichment in the western U.S. and elsewhere.

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Jackson, Jennifer M.0000-0002-8256-6336
Additional Information:Copyright © 2008 by the Geological Society of America. Manuscript received 13 May 2008. Revised manuscript received 19 August 2008. Manuscript accepted 26 August 2008. We thank Stefan Bernstein, Derek Schutt, and one anonymous reviewer for thorough reviews. This research was supported by National Science Foundation (NSF) grants EAR-9811870 and EAR-0510966. Jackson acknowledges support from NSF grants EAR-0711542 and EAR-0409321. The instruments used in the Chile Argentina Geophysical Experiment deployment were provided by the IRIS PASSCAL (Incorporated Research Institutions for Seismology Program for Array Seismic Studies of the Continental Lithosphere) Instrument Center. The data collected are available through the IRIS Data Management Center. The NSF under Cooperative Agreement EAR-0004370 supports the facilities of the IRIS consortium. GSA Data Repository item 2008238, tomography details, is available online at, or on request from or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
Group:Seismological Laboratory
Funding AgencyGrant Number
National Science FoundationEAR-9811870
National Science FoundationEAR-0510966
National Science FoundationEAR-0711542
National Science FoundationEAR-0409321
National Science FoundationEAR-0004370
Issue or Number:12
Record Number:CaltechAUTHORS:WAGg08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12865
Deposited By: Archive Administrator
Deposited On:08 Jan 2009 17:27
Last Modified:24 Jan 2020 18:40

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