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

one core and two fakes of porphyritic grey rhyolite obsidian from parque nacional monte león and the pali aike volcanic feld are chemically different than the more common black, banded grey-green and green obsidian types previously described from this area of southernmost patagonia. this porphyritic grey obsidian has higher concentrations of sr and ba and lower concentrations of zr, y, nb, th, hf and yb than these other three obsidian types. in these respects this obsidian resembles calc-alkaline rhyolite from andean volcanoes rather than the peralkaline rhyolite associated with patagonian back-arc basaltic plateau volcanism. however, this porphyritic grey obsidian has low sr/y (<20) and is chemically distinct from the adakitic (sr/y >30) erupted from volcanoes in the austral volcanic zone (49-54°s) of the southernmost andes, located directly to the west of monte león and pali aike. furthermore, no rhyolite obsidian has ever been identifed in these austral volcanoes. instead, these samples of porphyritic grey obsidian have visual and chemical similarities to porphyritic grey obsidian from the chaitén volcano (42°50’s) located over 1100 km to the northwest.