CARACTERIZACIÓN GEOLÓGICA DEL METAMORFISMO DIASTATERMAL MESOZOICO EN LA CUENCA NEUQUINA Y SU RELACIÓN CON LA ANOMALÍA TÉRMICA EN EL SINRIFT

The aim of this contribution is focused on the mineralogical, textural, and microstructural analysis of the very-low grade metamorphic rocks from Rahue-Chachil and the Cordillera del Viento syn-rift depocenters of the Neuquina basin. In addition, a geological characterization of the physical conditions of the metamorphism considered as regional and diastathermal type is provided. The thermal anomaly related to metamorphism was produced by the combination of the heat coming from the asthenospheric wedge of the extensional back-arc, the associated arc magmatism and the geothermal gradient by burial. The metamorphic pressure is of the lithostatic type with formation of compaction structures of meso- and microscale. The mineral associations and paragenesis indicate a metamorphic grade variable between prehnite-pumpellyite and zeolite facies for the rocks of the Precuyano Cycle, and between zeolite facies and diagenesis for those of the base of the Cuyo Group. The metamorphic grade increases towards the oldest rocks concomitantly with the increase in depth due to the lithostatic charge of the youngest rocks. The pressure-temperature-time (P-T-t) path of the rocks has a counter-clockwise trajectory and is characterized by metamorphic evolution of two segments, one prograde with peak temperature reached before peak pressure, and another retrograde with exhumation. The age of the metamorphism is constrained between the deposition of the rocks in the Upper Triassic-Lower Jurassic and the first episode of tectonic inversion of the basin, with the consequent exhumation of the depocenters from the Middle-Upper Jurassic.