Clustering of Pleistocene rock avalanches in the Central Andes, Argentina

MOREIRAS S.M.

Cenozoic Geology of Central Andes of Argentina

SCS Publisher

Año: 2011; p. 265 - 282

Three huge rock avalanche deposits with volumes in the order of one million cubic meters have been studied in detail in thenorthwestern Cordón del Plata range (32ºS). The diamictons are generally characterized by a poor sorting, but have a typical vertical succession of sediment facies. These rock avalanche events are inferred to have occurred during the late Pliocene-middlePleistocene based on stratigraphic relations with Pleistocene drifts previously studied along the Mendoza river valley and tephra layers overlaying both the glacial and rock avalanche deposits. The tephras have been Ar39-Ar40 dated to 350 ± 80 ka. This age is well correlated with the paleontological content found in an impounded paleolake consisting of dental pieces of Hippidion sp. A high magnitude earthquake is proposed as triggering mechanism based on geomorphological evidence, clustering of the rock avalanches, and present regional seismicity. The seismic activity was related to the Carrera fault system as lacustrine sediments are intensively deformed. These findings corroborate the assumption of Pleistocene activity of the regional faults. Nevertheless, warm paleoclimate conditions during late Pliocene-early Pleistocene could have favoured the occurrence of these events.