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Journal of Petrology Advance Access published online on September 21, 2006
Journal of Petrology, 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
Received June 13, 2005
Accepted August 23, 2006

Article

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

S. MAHLBURG KAY 1 *, A. A. ARDOLINO 2, M. L. GORRING 3, and V. A. RAMOS 4

1 EARTH AND ATMOSPHERIC SCIENCES, SNEE HALL, CORNELL UNIVERSITY, ITHACA, NY 14853, USA
2 DIRECCIÓN NACIONAL DE MINERÍA AND GEOLOGÍA, BUENOS AIRES, ARGENTINA
3 EARTH AND ENVIRONMENTAL STUDIES, MONTCLAIR STATE UNIVERSITY, UPPER MONTCLAIR, NJ 07043, USA
4 CIENCIAS EXACTAS AND NATURALES, CIUDAD UNIVERSITARIA, PABELLÓN II, 1428 BUENOS AIRES, ARGENTINA

* To whom correspondence should be addressed.
S. MAHLBURG KAY, E-mail: smk16{at}cornell.edu


  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.

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