Subsurface basement topography in the Cenozoic Andean foreland basin of northern Argentina: manifestations of long-wavelength deformation vs. inherited structures related to earlier orogeny and extensional processes

The distal Andean foreland basin (Chaco-Pampean Plain) is thought to have been tectonically inactive during the Cenozoic. However, re-interpreted industry seismic reflection data, borehole information and gravity surveys document a rich and complex history of tectonic activity. Our new data synopsis and re-analysis reveals two, regionally extensive and approximately N-S oriented, basement highs beneath the flat present-day surface. The Quirquincho (or Rincón Caburé) and Pampeano-Chaqueño highs have been observed by previous authors, but the mechanism that elevated these features and the timing has remained elusive. Here, we discuss several viable mechanisms of their formation. The morphology, wavelength and stratal terminations suggest that the Quirquincho high could represent a forebulge due to Paleogene orogenic processes. In contrast, the Pampeano Chaqueño high farther east might correspond to a Neogene forebulge, implying forebulge migration. Alternatively, both highs could have been caused by blind and associated with a major crustal detachment. In this case these processes may have been facilitated by vertical mechanical strength contrasts in the foreland crust that have been invoked to drive spatially and temporally disparate thick-skinned deformation during the Andean orogeny. The fact that the arches occur in the vicinity of Cretaceous normal faults and rift basins suggests that these highs could also have been linked with extensional processes; in this case basement uplift and erosion would have been followed by sedimentary processes that finally caused the onlap of the Paleogene strata on the arches. Finally, we also consider the possibility they are Paleozoic, inherited features with posterior reactivation.