Fragmentation of a foreland basin in response to out-of-sequence basement uplifts and structural reactivation: El Cajon-Campo del Arenal basin, NW Argentina

Abstract

The style and mechanisms by which a foreland region is incorporated into an orogen depends on the tectonic style, effectiveness of uplift, and dynamic subsidence. Classical foreland-basin models reflect a self-similar propagation of deformation into the foreland in a thin-skinned thrust-belt setting governed by wedge mechanics. Thick-skinned foreland regions, which are characterized by high-angle reverse-fault–bounded basement uplifts and intervening basins, however, do not fit this idealized model. Unlike thin-skinned tectonic provinces, deformation and uplift in these regions may be highly variable in time and space. Furthermore, deformation patterns may be complicated by the presence of preexisting structures, particularly those which lie at orientations that enable them to be reactivated and utilized to accommodated deformation under compression. The Neogene El Cajon–Campo del Are-nal basin is one of a series of basins located along the eastern margin of the Puna Plateau within the Sierras Pampeanas, a region that is composed of a thick-skinned foreland fragmented by reverse-fault–bounded basement uplifts that regionally characterize an eastward-younging trend. This region is superimposed onto the Cretaceous Salta Rift province, which provides a series of pre-existing structures that may potentially be reactivated. The basin is located along the eastern margin of the Puna Plateau, an integral component of the Andean orogen, which includes several filled, uplifted, and internally drained Cenozoic intraplateau basins. Structural and sedimentological similarities exist between basins along the margin of the Puna and those within it. Understanding the evolution of foreland basins, such as the El Cajon–Campo del Arenal basin, provides possible mechanisms for the development and incorporation of marginal basins into orogenic belts, and in the case of the Andean orogen, the potential for these basins to be incorporated into the plateau. Our analysis, which integrates seismic, sedimentary, and thermochronological data, characterizes the evolution of this basin and surrounding ranges. The appearance in the sedimentary section of a distinct grain-age population derived from the basement erosion surface constrains the uplift and erosion of an out-of-sequence intrabasin high to ca. 6 Ma. The basin fill, therefore, records an evolution from an undeformed foreland to one that is compartmentalized by basement uplifts and that is incorporated into the greater orogenic structure. The data reveal the importance of the reactivation of preexisting structures along the basin margin in creating east-dipping structures in a generally west-dipping domain. These opposing faults on the basin margin consequently caused the out-of-sequence uplift of the intrabasin range, the Sierra de Quilmes. The Sierra de Quilmes fragments the foreland and, because its position is locked by loads to the west and east, creates increased deformation within the basin, basin fill, uplift, and incorporation into the orogen. Unlike basins within the plateau, however, the El Cajon–Campo del Arenal basin has been re-excavated and integrated once more into the foreland drainage network.