Testing the occurrence of thick-skinned triangle zones in the Central Andes forearc: Example from the Salar de Punta Negra Basin in northern Chile

The Salar de Punta Negra Basin in the forearc of the Central Andes serves as a natural laboratory to understand the evolution of thick-skinned triangle zones dominated by opposite-verging, contractional systems. We combined field data and W-E 2D seismic profiles along parts of the basin where stratigraphic units are well constrained. The seismic data show the occurrence of thick-skinned triangle zones under the basin with along-strike variation. These are composed of west and east-verging, basement-involved faults and thrust ramps, or partially inverted normal faults. The plan-view structural configuration of the basin usually coincides with the sub-surface position of the triangle zones. The interplay between purely reverse and inverted faults in the region indicates that the thick-skinned triangle zones could be kinematically related to the superposition of two contractional episodes, consisting of: i) partial tectonic inversion of half-graben structures; and ii) basement deformation dominated by reverse faults and thrust and anticline ramps. The post-extensional tectono-sequences interpreted on the seismic profiles generally correlate with the Upper Cretaceous to Paleocene synorogenic successions exposed on surface, which allow us propose an age of deformation correlated with the “Peruvian” and “K-T” Andean Orogeny. The triangle zone could still be an active structure.