Historias eruptivas de volcanes cuaternarios en la región del Paso San Francisco, Andes Centrales

GROSSE, P.; GUZMÁN, S.

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentina; 2017

We reconstruct the eruptive histories of Incahuasi, Falso Azufre, El Cóndor and Peinado Quaternary volcanoes from the Paso San Francisco region (at ~27ºS, within the southern Central Volcanic Zone of the Andes: CVZ), based on field- and satellite image-based mapping, whole-rock geochemistry and unspiked K-Ar geochronology. Incahuasi consists of a main mostly andesitic conical edifice constructed between 1.6?0.7 Ma at a growth rate of 0.07 km3/ky. At 0.8?0.7 Ma activity shifted to the eastern flank, with the emplacement of a trachydacitic dome and a trachyandesitic lava field. At 0.35 Ma scoria cones and basaltic andesite lava flows were emplaced on the NE flank. Falso Azufre is an arcuate-shaped massif containing a Pliocene andesitic edifice remnant on its NW flank. The bulk of the massif is (trachy)-andesitic and was constructed between 0.9?0.5 Ma at a growth rate of 0.20 km3/ky. More recent activity (< 0.4 Ma) comprises mostly dacitic flows, coulées and domes restricted to the summit regions and the eastern flank. The overall Quaternary growth rate is 0.10 km3/ky. El Cóndor is a NW-SE elongated (trachy)-andesitic to (trachy)-dacitic massif with two distinct stages of activity, Pliocene and recent. Recent activity (< 0.13 Ma) is among the youngest recorded in the region and the estimated eruption rate of 0.37 km3/ky is one of the highest of the CVZ. Peinado, of basaltic trachyandesite to (trachy)-andesitic composition, is formed by a steep cone of lava, scoria and pyroclastic deposits surrounded by a lava flow ring emitted from five vents located around the base of the central cone. An age of 0.04 Ma evidences its youth. Incahuasi can be considered a young extinct volcano, Falso Azufre may be ongoing a minor felsic phase and can be considered potentially active, whereas El Cóndor and Peinado are possibly still in their main constructive phases and can be considered dormant active volcanoes.