Geochemical, isotopic and single crystal 40Ar/39Ar age constraints on the evolution of the Cerro Galán ignimbrites

Abstract

The giant ignimbrites that erupted from the Cerro Galn caldera complex in the southern Puna of the high Andean plateau are considered to be linked to crustal and mantle melting as a consequence of delamination of gravitationally unstable thickened crust and mantle lithosphere over a steepening subduction zone. Major and trace element analyses of Cerro Galn ignimbrites (68-71% SiO 2 ) that include 75 new analyses can be interpreted as reflecting evolution at three crustal levels. AFC modeling and new fractionation corrected 18 O values from quartz (+7.63-8.85) are consistent with the ignimbrite magmas being near 50:50 mixtures of enriched mantle ( 87 Sr/ 86 Sr0 .7055) and crustal melts ( 87 Sr/ 86 Sr near 0.715-0.735).