Cenozoic deformational processes in the North Patagonian Andes between 40º and 43ºS

Abstract

The Cenozoic tectonic evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformationalprocesses that acted through time and relate them to basin formation. Fieldobservations and seismic reflection profiles reveal the shallow structure of theretroarc area where contractional structures, associated with Oligocene to earlyMiocene inverted extensional sections, are partially onlapped by early to lateMiocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40° and 43° 30′S, constrained by surface, gravity, and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34 %) is determined near to 41° 30′S where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed toward the foreland. Additionally, eastward shifting of Miocene calc-alkaline arc rocks occurred at these latitudes, which is interpreted as indicative of a significant change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made also possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data.