Tectonics Associated with the Late Oligocene to Early Miocene Units of the High Andes (Cura-Mallín Formation). A Review of the Geochronological, Thermochronological, and Geochemical Data

The tectonic regime associated with the Oligo-Miocene Cura-Mallin Formation and equivalents in the Main Andean Cordillera between 35 degrees and 40 degrees S, the Ventana and Abanico formations to the south and north, respectively, is still matter of debate. While most authors have agreed in relating them to an extensional regime that could have interrupted Andean orogenesis, others have provided evidence of coexistence with an ongoing compressional regime at least for the upper part of their record. Available geochronological, structural, geochemical, thermochronological, and basin subsidence data between 33 degrees and 43 degrees S are compiled and analyzed in this chapter in order to provide a tectonic framework for these rocks. Based on this analysis, two different mechanisms seem to have succeeded through the accumulation of these sequences, a late Oligocene to earliest Miocene period characterized by syn-extensional deposits in an attenuated crust evidenced by low La/Yb ratios in contemporaneous magmatism, and a younger time period in the mid- to late Miocene that coincides with regional exhumation and compression revealed by thermochronological data and syncontractional sedimentation.