Analysis of subsurface data to characterize neotectonic structures in the Pampas plains, southwestern sector of the San Guillermo Elevated Block, Argentina

Abstract

Electrical resistivity tomography (ERT) and topographic profiles obtained by differential global positioning system were used to study depth continuity of structures showing neotectonic activity in the southwestern sector of the San Guillermo Elevated Block (SGEB), a morphostructural unit located in the Pampas region of Argentina. Data obtained from the surface and near-surface allowed us to identify the features of a fold caused by the propagation of high-angle reverse blind faults. Distribution of resistivities found in the near-surface seems to indicate westward propagation of the deformation front. One of the geoelectric levels interpreted in the ERT sections was used as a stratigraphic marker; the top of this level was compared with the depth found in wells drilled in different localities surrounding the study area, identifying lateral discontinuities that allow us to infer at least one stage of tectonic activity during the Pliocene–Early Pleistocene. The top of these deposits is shallower within the SGEB. On the other hand, the analysis of additional exploratory drilling allowed us to verify that the crystalline basement is fractured and is deeper than the western area outside the morphostructural unit. We propose that there are ancient pre-existing faults, created under an extensional regime, that were later reactivated involving multiple deformation events under a compressional regime. The normal displacement of crystalline basement blocks due to extensional tectonics would have been only partially inverted later during reactivation.

Graphical abstract

Schematic block diagram showing the electrical resistivity tomography (ERT) sections and the General Roca well projected at the latitude of the ERT, representing the interpreted folding (dashed line) and the difference in level of the stratigraphic marker of the Miocene Paraná/Puelches sands. The wider and deeper block diagram (down right) shows the normally-faulted crystalline basement at depth. Note that the ERT could be a tool to map the location of the fault tips, recently reactivated with reverse displacement. SGEB: San Guillermo Elevated Block.