Petrogenesis of the Triassic Cuyo basin magmatism: Controls on the magmatic evolution of passive rifts basins in Western Gondwana

Abstract

The rifting magmatism of the Cuyo basin (Western Argentina) is characterized by the presence of pyroclastic rocks and basaltic lavas, Triassic in age, emplaced during active faulting that occurred along an ancient terrane boundary. The pyroclastic rocks display calc-alkaline signature and were generated in shallow magma chambers with plagioclase fractionation associated with underplating processes. The basaltic lavas have alkaline to transitional composition with an OIB signature along with a negative Nb[sbnd]Ta anomaly and trace elements ratios that reflect crustal assimilation processes which are confirmed by their isotopic composition. Moreover, the Nd[sbnd]Sm isotopes suggest the involvement of a Precambrian upper crust in their genesis. The geochemistry of the basalts also reveals that the magmas generated in deep magma chambers that evolved through amphibole or garnet fractionation. Considering the geodynamic scenario, crustal assimilation processes could have been favored by the presence of highly fracturated ancient suture zones which could have promoted magma-host rock interaction during the magma ascent.