TWO NEW SUPERERUPTIONS IN THE ALTIPLANO-PUNA VOLCANIC COMPLEX OF THE CENTRAL ANDES

The Neogene ignimbrite flare-up (~10 to <1 Ma) in the Altiplano-Puna Volcanic Complex of the Central Andes is recorded in the products of several super-eruptions that have produced major calderas and ignimbrites totaling at least 11,000 km3 of magma and covering over 70,000 km2 in Chile, Bolivia, and Argentina. We have recently completed a new program of mapping, 39Ar-40Ar dating and paleomagnetic data collection that has established the sources for all the large ignimbrites in the Bolivian APVC. In particular, this effort has revealed two previously unknown super-eruptions and their sources. The Tara ignimbrite (3.49 ± 0.01 Ma), recognized as the younger ignimbrite ponded in the La Pacana caldera, is now confirmed as an eruptive product of the Guacha caldera to the north. It is the youngest super-eruption in the central APVC with exposures from around the Vilama caldera in the east to the Sol de Manana geothermal area to the west of Guacha. It crops out over an area of approximately 10,000 km2 and has a volume of at least 750 km3 (DRE). The other new supereruption involves the Pastos Grandes caldera. This was formerly thought to have formed during the 5.45 Ma eruption of the Chuhuilla ignimbrite. We now know that the Chuhuilla represents an earlier phase of activity at Pastos Grandes, and that the caldera structure, resurgence, and the main deposits are from the erupton of the Pastos Grandes Ignimbrite (2.89 ± 0.01 Ma). It is exposed over an area of approximately 6000 km2 and has a volume of at least 820 km3 (DRE). This is the youngest super-eruption in the APVC and makes Pastos Grandes the youngest resurgent caldera in the APVC. Our new results also support the long-lived, episodic nature of each of these systems and extend the period of ignimbrite production for the Pastos Grandes caldera from 5.5 Ma to 2.8 Ma and the Guacha caldera from 5.6 Ma to 3.5 Ma. These data also require that the global inventory of supereruptions be revised.