The Loncopué Trough: A Cenozoic basin produced by extension in the southern Central Andes

Abstract

The Loncopué trough is located in the hinterland Andean zone between 36º30´ and 39ºS. It constitutes a topographic low bounded by normal faults and filled by less than 5 Ma lavas and sediments. Reprocessed seismic lines show up to 1,700 m deep wedge-like depocenters associated with high- angle faults, correlated to the 27-17 Ma Cura Mallín basin deposits, buried beneath Pliocene to Quaternary successions and Late Miocene foreland sequences. The southern Central Andes seem to have been under extension at the hinterland zone some 27 Ma ago and again at approximately 5 Ma ago. This last extensional period could have been the product of slab steepening after a shallow subduction cycle in the area. Orogenic wedge topography, altered by the first extensional stage in the area, was recovered through Late Miocene inversion. However, since last extension (<5 Ma) the Andes have not recovered its characteristic contractional behavior that controlled past orogenic growth.