Onset of foreland basin deposition in the Neuquen Basin (34°-35°S): New data from sedimentary petrology and U-Pb dating of detrital zircons from the Upper Cretaceous non-marine deposits

A multi-proxy provenance approach using sedimentology, petrology and detrital zircon U-Pb geochronology provides new constrains for the evolution of the Southern Central Andes. The Upper Cretaceous non-marine deposits of the Neuquen Basin referred as Neuquen Group in the central and southern sector of the basin, have been characterized as the first foreland basin associated with the early uplift of the Andean orogen at ca. 100 Ma. However, in the northern sector of the basin, the stratigraphically equivalent Diamante Formation has not been studied in detail yet. This work focuses in the outcrops of the Diamante Formation located between Laguna del Diamante and Atuel River in southern Mendoza Province, Argentina (34 degrees-35 degrees S). The petrographic analysis of sandstones shows high content of volcanic and calcareous lithic fragments suggesting provenance from the underlying sedimentary units and the coeval volcanic arc associated with the onset of an important stage of deformation on the west. Detrital zircons from the base of the Diamante Formation were supplied sources from Upper Jurassic and Lower Cretaceous that were exposed during Upper Cretaceous times, whereas in the top, a high content of Permo-Triassic detrital zircons indicates exhumation of the surrounding Permo-Triassic crystalline basement. Finally, two maximum depositional ages were obtained, 107.2 +/- 1.4 Ma to Vega de los Patos and 91.1 +/- 2.2 Ma to Vega Grande, suggesting uninterrupted activity of the volcanic arc during foreland basin deposition. In particular, the age of 107.2 Ma would indicate that the sedimentation of the Upper Cretaceous non-marine deposits occurred in the Albian at these latitudes (34 degrees-35 degrees S), which suggests that the onset of the foreland basin sedimentation is diachronic at different positions in the Neuquen Basin.