Geoquímica y sistemática isotópica de rocas metamórficas del Paleozoico inferior. Noroeste de Argentina y Norte de Chile (21°-27° S)

R. BECCHIO, F. LUCASSEN, S. KASEMANN, G. FRANZ, J.G. VIRAMONTE

Abstract


Felsic rocks comprise more than 95% of the outcropping Early Paleozoic metamorphic basement. Their major and trace element contents and Pb, Rb-Sr and Sm-Nd isotope compositions are typical for upper crustal rocks. Sm-Nd model ages are ca 1.8 Ga. The principal ages of high-grade metamorphism is Early Paleozoic (ca 500 Ma). Recycling of this crust is the dominating process in the formation of granitoid magmatic rocks from Early Paleozoic to Recent. Ordovician sediments are also derivates of this crust. Felsic lower crustal xenoliths from the Salta Rift system are compositionally very similar compared to the early Paleozoic basement. The crustal composition from top to the bottom seems mainly felsic. Early Paleozoic mafic rocks are of minor volume and form mainly dikes. Their Sm-Nd model ages reveal two groups; one with ages of ca 1.8 Ga another with ages of £ 1.0 Ga. A meaningful interpretation of their geodynamic setting is not possible.

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