Mesozoic to Cenozoic deformation of the western Central Andes: an update from structural and U–Pb data of the Calama Basin and surrounding areas

The Mesozoic to Cenozoic deformation of the Andean forearc of northern Chile is interpreted as a mix of crustal extension, contraction, and strike-slip faulting, whose effects on the evolution of the western slope of the Central Andes have been largely debated. However, some topics, such as the initial distribution of the Pre-Andean structural and stratigraphic elements, the location, and nature of the main sediment sources active during the deformation, the timing of Andean uplift, and the location of synorogenic depocenters, are still unknown. In response to these questions and in order to update the previous knowledge about the tectonic evolution of Andean forearc, we developed a regional study of the Calama Basin and surrounding areas considering the occurrence of good exposures and availability of subsurface data. We integrated previous and new field data, two-dimensional seismic profiles, and zircon U–Pb ages from Mesozoic to Cenozoic units. Our results indicate a Triassic–Jurassic deformation dominated by rifting that progressed from an intracontinental domain, with the development of isolated half-grabens in the Triassic, to the opening of broad and marine rift-related basins during Jurassic times, thus confirming many of the interpretations made previously for the Pre-Andean evolution of northern Chile. The new ages of the continental post-rift units suggest that the rift system remained active at 95 Ma. After the post-rift, the Late Cretaceous orogenic history started with the inversion of preexisting Triassic and Jurassic rift-related structures, thus allowing the extrusion of syn-rift and post-rift strata. The latter is well outlined by the Chintoraste Fault exposed in the Loa and San Salvador rivers. During this period, the Andean deformation front was positioned in this region, and nearly 2 km of Upper Cretaceous to Paleocene synorogenic strata deposited on the inversion anticlines recorded this process. From the Eocene, an important basement-involved tectonism took place from the eastward migration of the Andean deformation front. The latter allowed the unroofing of the Paleozoic pre-rift basement blocks, thus creating a topographic relief dominated by contractional intermontane basins (e.g., the Calama Basin). These were filled by sediments eroded from the basement blocks (e.g., Sierra Limón Verde and Tuina sector) elevated by the reverse faults and by the Mio-Pliocene volcanic products of the magmatic arc.