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Journal of Petrology Advance Access originally published online on September 21, 2006
Journal of Petrology 2007 48(1):43-77; doi:10.1093/petrology/egl053
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

The Somuncura Large Igneous Province in Patagonia: Interaction of a Transient Mantle Thermal Anomaly with a Subducting Slab

S. Mahlburg Kay1,*, A. A. Ardolino2, M. L. Gorring3 and V. A. Ramos4

1Earth and Atmospheric Sciences, Snee Hall, Cornell University, Ithaca, NY 14853, USA
2Dirección Nacional de Minería and Geología, Buenos Aires, Argentina
3Earth and Environmental Studies, Montclair State University, Upper Montclair, NJ 07043, USA
4Ciencias Exactas and Naturales, Ciudad Universitaria Pabellón II, 1428 Buenos Aires, Argentina

RECEIVED JUNE 13, 2005; ACCEPTED AUGUST 23, 2006


  Abstract

The Oligo-Miocene Somuncura province is the largest (~55 000 km2) back-arc mafic volcanic field in Patagonia, and one of Earth's largest with no clear link to a hotspot or major extension. Major and trace element and Sr–Nd–Pb isotopic data suggest involvement of a plume-like component in the mantle magma source mixed with hydrous, but not high field strength element (HFSE)-depleted components, from a disintegrating subducting plate. Magmatism is attributed to mantle upwelling related to disturbances during plate reorganization, possibly at a time when the South America plate was nearly stationary over the underlying mantle. Melting was enhanced by hydration of the mantle during Paleogene subduction. Crustal contamination was minimal in a refractory crust that had been extensively melted in the Jurassic. Eruption began with low-volume intraplate alkaline mafic flows with depleted Nd–Sr isotopic signatures. These were followed by voluminous ~29–25 Ma tholeiitic mafic flows with flat light and steep heavy rare earth element (REE) patterns, intraplate-like La/Ta ratios, arc-like Ba/La ratios and enriched Sr–Nd isotopic signatures. Their source can be explained by mixing EM1–Tristan da Cunha-like and depleted mantle components with subduction-related components. Post-plateau ~24–17 Ma alkaline flows with steep REE patterns, high incompatible element abundances, and depleted Sr–Nd isotopic signatures mark the ebbing of the mantle upwelling.

KEY WORDS: Somuncura plateau; slab interaction; Patagonia; large igneous province (LIP); plume-like upwelling

*Corresponding author. Telephone: 1-607-255-4701. E-mail: smk16{at}cornell.edu


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