Geological evolution and structural control of the Cerro Blanco caldera, south-central Andes, northwestern Argentina

GROPELLI, G; GROPELLI, N; ARNOSIO, M; BECCHIO, R; JOSÉ GERMÁN VIRAMONTE; CORAZZATO,C.

Reykjavík

Simposio; IAVCEI General Assembly; 2008

IAVCEI

The Cerro Blanco caldera, located in the Puna Plateau, South-Central Andes, is 5 km in diameter and represents the youngest caldera of this Andean sector. Recently, Pritchard and Simons (2002; 2004), using radar interferometry, identified a subsidence in an area of 10 km in diameter with a maximum rate of 2.5 cm/a located in the south-eastern wall of the Cerro Blanco caldera. Viramonte et al. (2005), using high precision GPS network, confirm this subsidence with a maximum collapse of 1,73 cm/a at the caldera center. To reconstruct the geological and structural evolution of the Cerro Blanco caldera area, we executed remote sensing analyses (satellite, aerial and DEM images) and field survey. From the geological point of view, we recognize along the inner walls of the Cerro Blanco caldera the oldest succession, Miocene in age, La Hoyada volcanic complex. A wide gap in the eruptive history preceded the eruption responsible of the caldera forming, made of a widespread ignimbrite, named “Campo de la Piedra Pomez” (CPP, Late Pleistocene). After the caldera collapse, the volcanic activity developed along a 60°N oriented structure, mainly with the domes growing and collapses, filling partially the caldera depression. The last activity was characterised by phreatic and phreatomagmatic eruptions into the caldera depression where the 60°N fault system intersects a 140°N fault system. We assume that these two main fault systems were responsible and controlled the Cerro Blanco volcanic complex eruptions and the Cerro Blanco caldera forming. The persistent volcanic activity along the 60°N lineament suggests that this structure served as pathway for the rising of magma up to very recent time. Ongoing radiometric data (Viramonte et al., this congres) confirm the stratigraphic reconstruction and allow to better constrain the volcanic evolution and to evaluate the volcanic hazard of the area. Neotectonic evidences are constituted by some fault scarps located at the boundary of the area of active subsidence shown by interferometry and GPS survey, and they probably can account for part of the active deformation of the Cerro Blanco caldera.