The North Patagonian orogenic front and related foreland evolution during the Miocene, analyzed from synorogenic sedimentation and U/Pb dating (∼42°S)

Miocene sedimentary successions of the Nirihuau and Collon Cura formations east of the El Maiten Belt constitute a partial record of the Andean exhumation, defining a synorogenic infill of the Nirihuau Basin in the foothills of the North Patagonian fold and thrust belt. Gravimetric and seismic data allow recognizing the internal arrangement and geometry of these depocenters that host both units, separating a synextensional section previous to the Andean development at these latitudes, from a series of syncontractional units above. A series of progressive unconformities in the upper terms shows the synorogenic character of these units corresponding to the different pulses of deformation that occurred during the middle Miocene. New U-Pb ages constrain these pulses to the similar to 13.5-12.9 Ma interval and allow reconstructing the tectonic history of this region based on the detrital zircon source populations. The U-Pb maximum ages of sedimentation give to the Nirihuau Formation in particular a younger age than previously assumed. Additionally, synsedimentary deformation in strata of the upper exposures of the Collon Cura Formation associated with contractional structures and U-Pb ages allow identifying a younger paleoseismogenic pulse in 11.3 Ma. Thus, based on these data and a compilation of previous datasets, a tectonic evolution is proposed characterized by a contractional episode that migrated eastwardly since similar to 19 to 15 Ma producing the Gastre broken foreland and then retracted to the eastern North Patagonian Precordillera, where out-of-sequence thrusts cannibalized the wedge top zone in the El Maiten belt at similar to 13.5-11.3 Ma. (C) 2015 Elsevier Ltd. All rights reserved.