Luffi, Peter and Saleeby, Jason B. and Lee, Cin-Ty A. and Ducea, Mihai N. (2009) Lithospheric mantle duplex beneath the central Mojave Desert revealed by xenoliths from Dish Hill, California. Journal of Geophysical Research B, 114 . B03202. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20090413-075017646
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Low-angle subduction of oceanic lithosphere may be an important process in modifying continental lithosphere. A classic example is the underthrusting of the Farallon plate beneath North America during the Laramide orogeny. To assess the relevance of this process to the evolution and composition of continental lithosphere, the mantle stratigraphy beneath the Mojave Desert was constrained using ultramafic xenoliths hosted in Plio-Pleistocene cinder cones. Whole-rock chemistry, clinopyroxene trace element and Nd isotope data, in combination with geothermometry and surface heat flow, indicate kilometer-scale compositional layering. The shallow parts are depleted in radiogenic Nd (ε_(Nd) = -13 to -6.4) and are interpreted to be ancient continental mantle that escaped tectonic erosion by low-angle subduction. The deeper samples are enriched in radiogenic Nd (ε_(Nd) = +5.7 to +16.1) and reveal two superposed mantle slices of recent origin. Within each slice, compositions range from fertile lherzolites at the top to harzburgites at the bottom: the latter formed by 25–28% low-pressure melt depletion and the former formed by refertilization of harzburgites by mid-ocean-ridge-basalt-like liquids. The superposition and internal compositional zonation of the slices preclude recent fertilization by Cenozoic extension-related magmas. The above observations imply that the lower Mojavian lithosphere represents tectonically subcreted and imbricated lithosphere having an oceanic protolith. If so, the lherzolitic domains may be related to melting and refertilization beneath mid-ocean ridges. The present Mojavian lithosphere is thus a composite of a shallow section of the original North American lithosphere underlain by Farallon oceanic lithosphere accreted during low-angle subduction.
|Additional Information:||© 2009 American Geophysical Union. Received 30 June 2008; accepted 12 December 2008; published 5 March 2009. We kindly acknowledge assistance in xenolith field collecting from Lingsen Zeng and Zorka Saleeby. The manuscript greatly benefited from discussions with Paul Asimow, John Eiler, and Aniko Sandor. We are thankful for constructive reviews by Associate Editor Michael Bizimis, John Shervais, and an anonymous reviewer. Support was provided by the Gordon and Betty Moore Foundation to P. Luffi, by NSF grant EAR-0087347 to J. B. Saleeby, and by NSF EAR and EarthScope grants and the Packard Foundation to C.-T. A. Lee. This is contribution number 87 of Caltech Tectonics Observatory.|
|Group:||Caltech Tectonics Observatory|
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|Deposited By:||Tony Diaz|
|Deposited On:||03 Aug 2009 23:05|
|Last Modified:||26 Dec 2012 10:57|
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