Quaternary evolution of the El Tromen volcanic system, Argentina, based on new K-Ar and geochemical data: Insights for temporal evolution of magmatic processes between arc and back-arc settings

The new data coupled with those previously published highlight that, in the last 2 Ma, the Tromen Volcanic System (TVS) erupted transitional, alkali and rhyolitic lavas which built the Tilhué, Chapúa-Maipo-El Puente, Coyocho-Wayle and El Tromen volcanic groups. Four partial melting events have been identified: first at 2.10 ± 0.13 Ma, second at 1.44 ± 0.08 Ma, third at 1.04 ± 0.06 Ma and the last at 0.488 ± 0.007 Ma. Partial melting rates of the TVS sources are about 7% and constant, where first events affected simultaneously a shallower spinel-bearing mantle and a lower continental crust, and later ones a deeper garnet-bearing mantle. The melting of shallower, spinel-bearing, mantle released melts with low and middle-Ni, while the melting of deeper, garnet-bearing mantle, released relatively high-Ni melts. The lower continental crust affected by the first partial melting event could have been of sedimentary origin, thus producing the peraluminous Tilhué evolved lavas.