The Bajo Grande Basin: Late Jurassic(?)-Early Cretaceous syn-orogenic depocenters in southwestern Gondwana

Abstract

In recent years, multiple Mesozoic episodes of crustal shortening and extension have been documented throughout Patagonia. These findings unveil a complex history of regional intraplate tectonic deformation. Nevertheless, there are numerous sectors in this vast region that have yet to undergo in-depth tectonic investigations, and hence aspects of its evolutionary history remain elusive. We present herein a comprehensive dataset comprising geophysical data (2D seismic lines), field data (detailed geological mapping and lithofacies analysis), and UPb geochronological data (LA-ICP-MS and SHRIMP zircon ages) from a key region in southern Patagonia, known as the Bajo Grande area, located in the center of the Deseado Massif. The datasets support the hypothesis of a Late Jurassic(?) to Early Cretaceous shortening event that led to the tectonic inversion of former Jurassic (or may be older) extensional depocenters. This episode promoted the syn-inversion (syn-orogenic) deposition of Late Jurassic(?)-Early Cretaceous (140 ± 3 Ma) epiclastic and pyroclastic rocks within NNE-striking depocenters. These rocks are part of the Bajo Grande Formation, representing one of the oldest documented syn-orogenic sequences in southern Patagonia. This shortening event may have been triggered by a far-field response to the opening of the Rocas Verdes basin and to the rift-drift transition of the South-Atlantic Ocean.