Caracterización geológica del metamorfismo diastatermal mesozoico en la Cuenca Neuquina y su relación con la anomalía térmica en el sinrift

Abstract

A mineralogical, textural, and microstructural analysis as well as a characterization of the physical conditions of the regional and diastathermal metamorphism of the very-low grade metamorphic rocks from Rahue-Chachil and the Cordillera del Viento syn-rift depocenters are presented. The thermal anomaly related to metamorphism results from a combination of heat coming from the asthenospheric wedge of the extensional back-arc, the associated arc magmatism and the geothermal gradient by burial. Meso- and microscale compaction structures indicate that the metamorphic pressure is lithostatic. The mineral associations and paragenesis point to 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. A counter-clockwise trajectory of the pressure-temperature-time (P-T-t) path is depicted and characterized by two contrasting segments, one prograde with peak temperature predating peak pressure, and another retrograde with exhumation. The age of the metamorphism is constrained between the deposition of the rocks in the Late Triassic-Early Jurassic and the first episode of tectonic inversion of the basin, with the consequent exhumation of the depocenters from the Middle-Upper Jurassic.