Cenozoic exhumation of the Frontal Cordillera revisited: Insights from low-temperature thermochronology studies and other geological constraints

Abstract

The Frontal Cordillera is a prominent north–south-trending morphostructural feature in the southern Central Andes, characterized by high topography and relief,monotonic lithologic exposures of Late Paleozoic to Triassic volcanic and intrusive rocks, and thick-skinned deformation. It spans from ~27 to 28◦S, where itgradually transitions into the Puna Plateau, to 34.8◦S, where it terminates abruptly. Most of the along-strike exposure of this tectonic domain coincides spatially withthe modern Argentina-Chile (Pampean) flat-slab subduction segment (27–33◦30′S). Early studies attributed the construction of the Frontal Cordillera to enhancedtransmission of compressional stresses to the overriding plate during the Middle Miocene–Recent southward migration of flat-slab subduction, and the associatedpropagation of deformation to the foreland. However, recent studies have questioned north-to-south diachronism in the structural evolution of the Frontal Cordillera,as well as the extent to which uplift and exhumation were controlled by flat-slab subduction. The timing of deformation in the Frontal Cordillera has been primarilyconstrained through the analysis of synorogenic sedimentary records and crosscutting structural relationships. Thermochronological studies have emerged asadditional, powerful tools for quantifying the exhumation of ranges that comprise the Frontal Cordillera. Despite the proliferation of structural, sedimentological,geo/thermochronological, and geomorphic studies in recent years, fundamental aspects –including the timing and patterns of rock uplift and exhumation in theFrontal Cordillera, and the overall vergence of the Andean orogenic wedge at these latitudes– remain topics of debate. This contribution presents an updated reviewof thermochronological studies carried out in the Frontal Cordillera in recent years, and the implications of these data for regional tectono-thermal evolution in thecontext of other, independent geologic constraints. Our data compilation reveals that the main phase of rock uplift and exhumation preceded the onset of flat-slabsubduction and occurred largely synchronously along strike during the Early to Middle Miocene. This phase of deformation overlapped with the final stages ofcontraction in the Principal Cordillera to the west, suggesting an east-directed propagation of deformation. The results also point to a period of pronounced crustalshortening during the Early Miocene, marked by the simultaneous activity of multiple tectonic domains within the Andean wedge.