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Journal of Petrology Advance Access published online on November 6, 2009
Journal of Petrology, doi:10.1093/petrology/egp072
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© The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Lithospheric Removal as a Trigger for Flood Basalt Magmatism in the Trans-Mexican Volcanic Belt

Laura Mori1,*, Arturo Gómez-Tuena2, Peter Schaaf3, Steven L. Goldstein4, Ofelia Pérez-Arvizu2 and Gabriela SolÍs-Pichardo1

1Instituto de GeologÍa, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico
2Centro de Geociencias, Universidad Nacional Autónoma de México, 76230 QueréTaro, Mexico
3Instituto de Geofísica, Universidad Nacional AutóNoma de México, 04510 Mexico City, Mexico
4Lamont–Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, New York, NY 10964, USA

Received February 10, 2009; Revised typescript accepted October 1, 2009


  Abstract

The voluminous succession of tholeiitic basalts, calc-alkaline andesites and minor high-K basalts that form the Late Miocene Altos de Jalisco mafic province of the western Trans-Mexican Volcanic Belt is interpreted as the magmatic manifestation of a lithospheric dripping event, which removed mantle lithosphere and lower crustal lithologies beneath the study area. During this process, the release of fluids from the foundering materials, coupled with mantle upwelling around the sinking mass, promoted abundant melting of a spinel peridotite and the production of large volumes of tholeiitic magma with low La/Yb and Gd/Yb ratios. Negative correlations of these ratios with MgO contents, Nd isotopes and Rb/Nd ratios indicate that the parental basalts subsequently experienced high-pressure fractional crystallization and contamination with a newly exposed felsic continental crust, thus producing the more evolved calc-alkaline compositions. Stronger garnet signatures and marked enrichments in highly incompatible elements in the high-K suite support derivation from a garnet- and phlogopite-bearing pyroxenitic source, presumably formed by reaction of mantle peridotites with hydrous silicic melts derived from the foundering lithologies. This new petrogenetic model for the Altos de Jalisco volcanic district suggests that the loss of mafic lower crust during lithospheric dripping might be balanced by production of abundant flood basalts within continents, and thus indicates that additional mechanisms may be required for the stabilization of andesitic crust on Earth.

KEY WORDS: continental flood basalts; high-K magmas; lithospheric removal; mantle; Trans-Mexican Volcanic Belt

* Corresponding author. Telephone: +52 55 56224329, 206. Fax: +52 55 56224317. E-mail: lmori{at}geologia.unam.mx


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