A buried Middle Miocene caldera beneath Laguna Pozuelos, Northern Puna?

PREZZI, CLAUDIA BEATRIZ; LINCE KLINGER, FEDERICO; CAFFE, PABLO; GIMENEZ, MARIO

Santiago de Chile

Congreso; Geosur 2007; 2007

In the southern border of Laguna de Pozuelos, the Pan de Azúcar volcanic complex crops out. It consists of several volcanic dome centers of ~ 12 Ma. Previous interpretation of seismic lines and a detailed ground magnetic survey indicated the presence of buried intrusive bodies. The determination of the existence of buried bodies has two major implications:  1) these volcanic complexes are closely associated with ore deposits (as part of the Bolivian tin ore polymetallic belts); 2) the existence of a large ancient caldera (~ 12Ma) beneath the central and southern part of the Laguna de Pozuelos Basin, covered by the infilling sediments was suggested. The volcanic complexes (Cerro Redondo, Chinchillas, Pan de Azúcar) would represent the final stages of such a calderic magmatic system. Detailed ground gravity and magnetic surveys were carried out. The magnetic map is dominated by positive (maximum of 210 nT) and negative (minimum of -280 nT) anomalies in the southern sector of the basin, associated with the dacitic domes. The residual Bouguer anomaly presents a semicircular pattern, having only positive values which range between 36 and 60 mGal, with the lowest values to the east of Cincel river. We applied the curvature technique to analyse the magnetic and gravity signals and used Euler deconvolution to estimate the depth to the sources. The Cincel river is supposed to follow a large-scale ring fracture that would define the eastern limit of the buried calderic system. Our results would support the hypothesis of a large caldera buried beneath the Laguna de Pozuelos Basin. The identification of such a large Middle Miocene caldera would bring new insight into the magmatic evolution of the northern Puna.