Caracterizacion petrológica y geoquímica de volcanes estrombolianos en la porcion norte del Valle Calchaqí, Salta.

GUZMÁN, S. R; PETRINOVIC, I. A.; BROD, J. A.

Cabo Frío

Congreso; III Simpósio Sobre Vulcanismo E Ambentes Associados; 2005

GSB

Abstract – Los Gemelos and El Saladillo are a set of mafic, monogenetic volcanoes of strombolian character in the northern Calchaquí valley, on the boundary between the Puna and the Cordillera Oriental. They constitute the easternmost recognized examples of mafic Plio-Quaternary volcanism in the southern Central Andes. Magmas derived from a small degree of partial melting of an enriched, garnet-bearing mantle source. The analysed rocks have primitive signature (high Ni, Cr, Co and MgO concentrations; presence of chromite and forsteritic olivine) and evidence for crustal contamination with felsic, radiogenic rocks (quartz ± plagioclase ± K-feldspar xenocrysts with coronas, reaction rims and/or embayments; high 87Sr/86Sr ratios, negative D Nd values). The high Cr and Ni content, high Mg# and low crystal content (<25 %) suggest that major fractional crystallization did not take place, therefore precluding long residence periods. Rapid magma ascent across 50 km of continental crust was guided by magmatic overpressure favoured by important tectonic stresses. Thus, we invoke a process of assimilation during turbulent ascent (ATA) to explain the contamination at crustal levels.t – Los Gemelos and El Saladillo are a set of mafic, monogenetic volcanoes of strombolian character in the northern Calchaquí valley, on the boundary between the Puna and the Cordillera Oriental. They constitute the easternmost recognized examples of mafic Plio-Quaternary volcanism in the southern Central Andes. Magmas derived from a small degree of partial melting of an enriched, garnet-bearing mantle source. The analysed rocks have primitive signature (high Ni, Cr, Co and MgO concentrations; presence of chromite and forsteritic olivine) and evidence for crustal contamination with felsic, radiogenic rocks (quartz ± plagioclase ± K-feldspar xenocrysts with coronas, reaction rims and/or embayments; high 87Sr/86Sr ratios, negative D Nd values). The high Cr and Ni content, high Mg# and low crystal content (<25 %) suggest that major fractional crystallization did not take place, therefore precluding long residence periods. Rapid magma ascent across 50 km of continental crust was guided by magmatic overpressure favoured by important tectonic stresses. Thus, we invoke a process of assimilation during turbulent ascent (ATA) to explain the contamination at crustal levels.