Neogene evolution of the Aconcagua fold-and-thrust belt: Linking structural, sedimentary analyses and provenance U-Pb detrital zircon data for the Penitentes basin

Abstract

The Neogene Penitentes basin registers the earliest synorogenic infill in an inner region of the southern Central Andes, between Principal and Frontal cordilleras at 33°S, which contrast with other Neogene basins that are distributed to the east, in the foreland area. In this work, we focused on the study of the first infill of the basin, the Penitentes Conglomerate, which crops out along the Aconcagua fold-and-thrust belt (Principal Cordillera). We carried out sedimentological, geochronological, and structural studies to better understand the genesis and evolution of these synorogenic deposits. We recognized the Penitentes Conglomerate at the Blanco river and the Potrero Escondido creek, located to the south of the previously established boundaries of the basin. We obtained a maximum depositional age of 15 ± 1 Ma (weighted mean 206Pb/238 U age; n = 8; MSDWD = 4.5; error of 95% conf.) for the base of the Penitentes Conglomerate in the Potrero Escondido creek. Based on clast composition and U-Pb detrital zircon ages of the Penitentes Conglomerate base, the provenance analysis reflects the Aconcagua's fold-and-thrust belt exhumation to the west of the basin. The denudation processes that affected the Principal Cordillera generated an unroofing sequence within the Penitentes Conglomerate. In contrast, towards the top of the sequence, the Penitentes Conglomerate has sediment input derived from eastern sources, which indicates that the Frontal Cordillera was exhumed and acted as a sediment source area for the Penitentes basin by the Middle Miocene (~14 Ma). In this sense, the chronology of the uplift of Principal and Frontal cordilleras agrees with the east-vergent orogenic model for the Andes. The structural analyses presented in this paper show a minimum shortening of 62% for the Aconcagua fold-and-thrust belt with an out-of-sequence deformational phase during the mid-late Miocene, after the uplift of the Frontal Cordillera.