New insights on the origin of the Mesón Alto deposit, Yeso Valley, central Chile: A mix of glacial and landslide deposits?

DECKART K., PINOCHET K., SEPÚLVEDA S., PINTO L., MOREIRAS SM.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2014 vol. 41 p. 248 - 258

0718-7092

The Mesón Alto chaotic deposit, located in the Principal Cordillera at about 33°40?S, is an important landform with a volume of ca. 4.5 km3 unconsolidated material deposited downstream of the Yeso water reservoir in the Yeso Valley, Río Maipo drainage basin. Historical work related this large deposit to a glacial origin whereas later on, it was assigned to a megalandslide originated in the Cerro Mesón Alto massif. First results of an integrated field, petrographic and geochemical laboratory work on granitoid blocks from five different portions of the deposit compared with the major outcropping intrusive units in the neighbourhood which are La Gloria pluton, Cerro Mesón Alto massif and Cerro Aparejo intrusion point to a landslide origin of the surface blocks. The resuIts suggest that granitoids fragments of the deposit most likely belong to the Cerro Mesón Alto massif where the rock avalanche was sourced. However, morphometric parameters and field observations support the idea of a rock avalanche placed on top of glacial material that should contain blocks of La Gloria pluton and Cerro Aparejo intrusion as well. Therefore, the Meson Alto deposit is assigned to a mixed origin.