NEW STRUCTURAL DATA OF THE BAJO GRANDE AREA, SANTA CRUZ PROVINCE, ARGENTINA

MAXIMILIANO PEREZ FRASETTE; CÉSAR NAVARRETE; ANDRÉS FOLGUERA

Simposio; XVIII Reunión de Tectónica; 2021

The Bajo Grande area is located in the central sector of the Deseado Massif, in the Santa Cruzprovince of Argentina. In this area, there are outcrops of the Bahía Laura Volcanic Complex (BLVC) thatinclude the Bajo Pobre, Chon-Aike and La Matilde formations, as well as the Bajo Grande Formation andthe Baqueró Group (Panza et al. 2001). Several studies have been conducted on the BLVC and theBaqueró Group in several sectors of the Deseado Massif (e.g., Navarrete et al. 2020; Passalia et al. 2016),however the knowledge about the Bajo Grande Formation is poor. Hechem and Homovc (1988) carriedout a lithological description and a paleoenvironment interpretation of this unit, whereas Giacosa et al.(2010) described a remarkable angular unconformity between the Bajo Grande Formation and theoverlying Baqueró Group. This contact shows the Baqueró Group lying horizontally on the Bajo GrandeFormation, which dips westward.In this contribution, we present a new geological detailed map, which added to the interpretationof two 2-D seismic lines registered by YPF S.A. in the `90s, allow us to elaborate a novel tectonic modelfor the evolution of the Bajo Grande area.Two major NE-SW long wavelength anticlines and a syncline were identified on the surface. The firstis an anticline located at the western sector of the Bajo Grande area, which was produced by the positivetectonic inversion of a normal fault here referred as the Bajo Grande Fault. Its flanks are comprised ofthe Bajo Grande Formation, whereas the La Matilde Formation constitutes the core of the fold. Thesecond anticline is situated at the eastern sector of the Bajo Grande area, and its core exposes the BajoPobre Formation. The western flank exhibits rocks of the Bajo Grande, La Matilde and Bajo Pobreformations, whereas the eastern flank is only constituted by the Bajo Pobre Formation. This fold ispreliminarily interpreted as the result of tectonic inversion of a normal fault here referred to asGobernador Moyano Fault. Finally, the third structure is a syncline formed in the central sector betweenthe two anticlines.The structural relationships observed in surface and in the seismic information between the studiedunits allow us to propose that the fold system would have been originated by the tectonic inversion ofprevious Jurassic extensional structures. Further, the wedge-shape Bajo Grande Formation would suggestits synorogenic deposition.