Late Cretaceous orogenic front in the Southern Central Andes

LUCAS FENNELL; GUIDO GIANNI; MAXIMILIANO NAIPAUER; ANDRÉS FOLGUERA

Santiago

Congreso; I Simposio de Tectónica Sudamericana; 2016

Late Cretaceous deformation in the Southern Central Andes has been a matter of discussion during thelast 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 hadalready been brought to light by the first naturalists that described the geology at these latitudes, thedifficulty to study old deformational phases that have been reprinted by new ones simplified thegeological models and the Andean rich history was shortened to Miocene times onwards. Since it?simpossible to reconstruct its physiognomy, the best way to understand the initial Andean orogen is tostudy its associated foreland basin at these latitudes, the Neuquén Group. Studies performed in this unithave already shown that its base lies in angular unconformity or disconformity over Lower Cretaceousdeposits, 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 andlacustrine deposits accumulated during 25 Ma in a foreland basin, which can be separated in twodepozones: the wedge top and foredeep areas. The wedge top depozone is where structuration andsedimentation processes take place at the same time, so in order to infer its position within the forelandbasin, the classical way is through the identification of growth strata, which in turn serve as an indicatorof the migration of the orogenic front. Growth strata have been identified in Neuquén Group outcropsassociated to the main anticlines of the Malargüe fold and thrust belt and, through the sampling of acomplete 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 newthermochronological and seismic data and the location of growth strata, we were able to infer the upliftedstructures, the paleoflow of sediments and the location of intermontane basins. Also, a review of thegeodynamic 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 theAndes is proposed.