Late Cretaceous orogenic front in the southern Central Andes (35°-37°S)

NAIPAUER MAXIMILIANO; FOLGUERA ANDRÉS; FENNELL LUCAS; GIANNI GUIDO

Santiago de Chile

Simposio; Primer Simposio de Tectónica Sudamericana; 2016

Late Cretaceous deformation in the Southern Central Andes has been a matter of discussion during the last years, but the idea of the onset of structuration of the Malargüe fold and thrust belt during these times, in line with the rest of the Andean range, is nowadays starting to be accepted. Although this concept had already been brought to light by the first naturalists that described the geology at these latitudes, the difficulty to study old deformational phases that have been reprinted by new ones simplified the geological models and the Andean rich history was shortened to Miocene times onwards. Since it?s impossible to reconstruct its physiognomy, the best way to understand the initial Andean orogen is to study its associated foreland basin at these latitudes, the Neuquén Group. Studies performed in this unit have already shown that its base lies in angular unconformity or disconformity over Lower Cretaceous deposits, representing ca. 25 Ma of erosion, structuration and absence of deposition. Later, at 100 Ma, constrained by the maximum age of sedimentation in U-Pb dating of detrital zircons, fluvial, aeolian and lacustrine deposits accumulated during 25 Ma in a foreland basin, which can be separated in two depozones: the wedge top and foredeep areas. The wedge top depozone is where structuration and sedimentation processes take place at the same time, so in order to infer its position within the foreland basin, the classical way is through the identification of growth strata, which in turn serve as an indicator of the migration of the orogenic front. Growth strata have been identified in Neuquén Group outcrops associated to the main anticlines of the Malargüe fold and thrust belt and, through the sampling of a complete profile of this unit, provenance analysis were performed with U-Pb detrital zircon age patterns. Through the comparison with other provenance studies, the recent appearance of new thermochronological and seismic data and the location of growth strata, we were able to infer the uplifted structures, the paleoflow of sediments and the location of intermontane basins. Also, a review of the geodynamic scenario in Late Cretaceous times allowed understanding the link between magmatism, structuration and sedimentation at these latitudes, and a potential connection with other areas along the Andes is proposed.