INTEGRATED STRATIGRAPHIC APPROACH TO DEFINING THE DYNAMICS OF THE RINCON BLANCO HALF-GRABEN AND ITS TECTONIC RELATIONSHIP

After the cease of subduction in Gondwana an important back-arc extension favored the development of rifts basins along its western margin. They consisted of northwest-trending troughs composed of asymmetric half-grabens. In these basins, active extensional faulting and sedimentation are intimately linked so the architecture and fill are influenced by the geometry and the displacement of the bounding normal faults and thus their features can be extracted from the sedimentary record.

A particular focus in this has been applied in the Rincón Blanco subbasin that helped unravel its complex history despite the Tertiary uplift and partial inversion that buried almost the entire master fault. Using lithology and structural data the infilling was subdivided into packages of genetically linked units bounded by regional extended surfaces. Hence, two depositional sequences or tectono-stratigraphic units separated by a regional unconformity have been recognized. This latter is interpreted as a result of a major reactivation of the extensional system or second stage of rifting. Additionally, the Rincón Blanco master fault, a mostly normal-slip fault with highest displacement toward the center, was segmented forming echelon geometries that resulted in the development of two subbasins separated by a transfer zone. The oldest strata filled the northernmost segment (Marachemill Unit) while younger strata filled a southern one (Rincón Blanco Group). Because of the new extensional event, individual fault segments lengthen linking the originally isolated depocenters and skewing the point of maximum displacement toward the zone of overlap where deep lacustrine facies developed (Carrizalito Formation).

When compared with other subbasins (Puntudo, Uspallata and Ischigualasto -Villa Union), they all experienced similar tectono-stratigraphic histories that suggest a notable intra-Triassic tectonic event. It is suggested here that this remarkable event could be related to the steepening of the subducted plate occurred during Middle Triassic as proposed by Martinez (2005).