Obsidiana gris porfírica calco-alcalina del volcán Chaitén en sitios arqueológicos al sur del río Santa Cruz, Patagonia meridional

CHARLES R. STERN, SOLEDAD CARACOTCHE, ISABEL CRUZ Y JUDITH CHARLIN

Magallania

Universidad de Magallanes

Año: 2012 vol. 40 p. 135 - 142

0718-0209

One nodule and three other fragments of porphyritic grey rhyolite obsidian from P.N. Monte León and Pali-Aike volcanic field are chemically different than the more common black, banded grey-green and green obsidian types previously described from this area of southernmost Patagonia. This grey obsidian has higher concentrations of Sr and Ba and lower concentrations of Zr, Y, Nb, Th, Hf and Yb than these three other obsidian types. In these respects this obsidian resembles calc-alkaline rhyolite from recent Andean volcanoes, such as Chaitén, rather than the peralkaline obsidian associated with Patagonian back-arc basaltic plateau volcanism. The source of this dark grey obsidian must still be considered as unknown, despite its intriguing visual and chemical similarities to porphyritic grey obsidian from Chaitén volcano.