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Geochemical Evidence for Slab Melting in the Trans-Mexican Volcanic Belt |
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| Authors: | Gomez-Tuena Arturo; Langmuir Charles H; Goldstein Steven L; Straub Susanne M; Ortega-Gutierrez Fernando |
| Institution: | 1Centro de Geociencias, Universidad Nacional Autónoma de México, Querétaro 76230, Mexico 2Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA 3Lamont–Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University, 61 RT. 9W, Palisades, NY 10964, USA 4Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MEXICO |
| Abstract: | Geochemical studies of Plio-Quaternary volcanic rocks from theValle de Bravo–Zitácuaro volcanic field (VBZ) incentral Mexico indicate that slab melting plays a key role inthe petrogenesis of the Trans-Mexican Volcanic Belt. Rocks fromthe VBZ are typical arc-related high-Mg andesites, but two differentrock suites with distinct trace element patterns and isotopiccompositions erupted concurrently in the area, with a traceelement character that is also distinct from that of other Mexicanvolcanoes. The geochemical differences between the VBZ suitescannot be explained by simple crystal fractionation and/or crustalassimilation of a common primitive magma, but can be reconciledby the participation of different proportions of melts derivedfrom the subducted basalt and sediments interacting with themantle wedge. Sr/Y and Sr/Pb ratios of the VBZ rocks correlateinversely with Pb and Sr isotopic compositions, indicating thatthe Sr and Pb budgets are strongly controlled by melt additionsfrom the subducted slab. In contrast, an inverse correlationbetween Pb(Th)/Nd and 143Nd/144Nd ratios, which extend to lowerisotopic values than those for Pacific mid-ocean ridge basalts,indicates the participation of an enriched mantle wedge thatis similar to the source of Mexican intraplate basalts. In addition,a systematic decrease in middle and heavy rare earth concentrationsand Nb/Ta ratios with increasing SiO2 contents in the VBZ rocksis best explained if these elements are mobilized to some extentin the subduction flux, and suggests that slab partial fusionoccurred under garnet amphibolite-facies conditions. KEY WORDS: arcs; mantle; Mexico; sediment melting; slab melting |
| Keywords: | : arcs mantle Mexico sediment melting slab melting |
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