Abstract

BERTOTTO, Gustavo Walter et al. Petrografía y geoquímica del centro eruptivo basáltico Toscales, zona de retroarco Extraandino de la provincia de Mendoza. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.3, pp.330-340. ISSN 0004-4822.

The Toscales eruptive center is located in the southeast of the Mendoza province and represents one of the farthest manifestations of Cenozoic back-arc volcanism from the subduction zone within Payenia. It consists of a lava flow, dikes and pyroclastic deposits of basaltic composition. These rocks have porphyritic texture with trachytic, hyalophitic and hyalopilitic groundmass. The phenocryst is olivine; the association of the groundmass is plagioclase, olivine, clinopyroxene, opaque minerals and glass. From their chemical composition, the analyzed rock sample classified as alkaline basalt in the TAS diagram. The trace element concentrations, normalized to primitive mantle, have a pattern with negative anomalies of Nb-Ta, Zr-Hf and Ti, signatures that are typical of volcanic arc basalts of the Andean Southern Volcanic Zone and similar to transitional basalts from Patagonia. The rare earth element (REE) pattern is within the range of variation of the surrounding Pleistocene basalts. Based on non-modal fractional melting model, the REE pattern corresponds to one generated by 1% partial melting of a garnet-bearing lherzolite having the primitive mantle composition. The new K-Ar age obtained (3.48 +/- 0.27 Ma) indicates that the Toscales eruptive center was part of the widespread late Pliocene-Pleistocene back-arc volcanic activity in the region.

Keywords : Basalts; Pliocene; Payenia.

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