Jurassic intraplate contraction of southern Patagonia: The El Tranquilo Anticline area, Deseado Massif

Abstract

A late Early Jurassic shortening event affected the southern end of the back-arc Chubut Basin in southern Patagonia, interspersed within a general lithospheric extensional context linked to Gondwana breakup. In this work, we report this episode through field and 2D seismic data in the El Tranquilo Anticline area, at the central portion of the Deseado Massif. In this area, a series of folds affecting the Roca Blanca Formation (Lower Jurassic) has been recognized underlying unconformably subhorizontal volcanic rocks of the Bahía Laura Volcanic Complex (Lower to Upper Jurassic). We used 2D seismic data to examine contractional structures linked to positive tectonic inversion of NNW Permian to Early Jurassic extensional faults at depth. Additionally, we describe non-deformed epithermal veins of Middle to Late Jurassic age, intruding contractionally deformed rocks of the Roca Blanca Formation and the El Tranquilo Group (Middle to Upper Triassic) in the central sector of the El Tranquilo Anticline area. The latter, gives further evidence for the existence of a late Early Jurassic contractional event in this area. This evidence constitutes the southernmost record of transient Jurassic shortening in Patagonia that interrupted temporarily widespread lithospheric extension associated with southern Pangea breakup.