Constraints for recently discovered ignimbrites in the Altiplano-Puna Volcanic Complex (APVC), northern Chile

Abstract:

One of most voluminous ignimbrite provinces in the world (>30.000 km³) is located in the Central Andean Volcanic Zone (CAVZ), which has been continuously active since Upper Oligocene. Altiplano-Puna Volcanic Complex (APVC), located between 21 and 24ºS, is a volcano-tectonic province constituted by diverse caldera complexes and ignimbrite deposits (Upper Miocene – Lower Pleistocene) that covers an area ~50.000 km². In this work, we present data from three new ignimbrites discovered in a portion of APVC (22°–22,4°S), with the objective to establish its origin and provenance. Were identified 3 new ignimbrites: 1) Cabana ignimbrite (>7.5 Ma), constituted by 3 pyroclastic flow and 1 pyroclastic surge units of crystal-glass rich dacitic tuffs, 80 m maximum thick, 0.18 km³ volume and 0.14 km³ DRE; 2) Inacaliri ignimbrite (7.5 Ma) constituted by two members, corresponding to glassy dacitic (basal member) and basaltic andesites (upper member) tuffs, the total thick reach up 20 m, 0.003 km³ volume and 0.002 km³ DRE; 3) Tolar ignimbrite (>1.3 Ma), constituted by a single pyroclastic flow and a basal fall glassy dacitic deposits, 50 m maximum thick, 0.04 km³ volume and 0.03 km³ DRE. Cabana ignimbrite seems to have been originated from a single caldera complex, whose cannot be recognized in the field. Inacaliri ignimbrite could be related to initial phases of building of Inacaliri and Apacheta-Aguilucho volcanic complexes, or originated to a buried caldera located below both volcanic complexes. Finally, Tolar ignimbrite corresponds to initial building stage of Toconce volcano, located 2 km at NE from these deposits.