Analyzing the transition from extension to contraction at the North Patagonian Andes

FLORENCIA BECHIS; ALFONSO ENCINAS; VÍCTOR VALENCIA; VICTOR A. RAMOS

La Serena

Congreso; XIV Congreso Geológico Chileno; 2015

Colegio de Geólogos de Chile y Sociedad Geológica de Chile

A long segment of the Southern Central Andes underwent extensional tectonics during the Oligocene to Early Miocene. As a result, a series of complex extensional basins filled with volcanic products and marine and/or continental sedimentary rocks developed along the margin in either fore-, intra-, and retro-arc positions. The infill of some of these basins records a transition to a compressive tectonic regime that became predominant all along the segment by the Late Miocene. In this contribution, we address the timing of the transition from extension to contraction tectonics in the Ñirihuau basin, which developed in an intra- to retro-arc position in the North Patagonian Andes between 41° and 43°S. We integrate new and previous geochronologic, structural and stratigraphic data in order to constrain the timing of the onset of shortening by analyzing the tecto-sedimentary evolution of the basin infill. Our results indicate that the tectonic switching in the eastern sector of the North Patagonian Andes is registered in different depocenters of the Ñirihuau basin and that the transition took place between 16-15 and 13 Ma (Middle Miocene).