Structural evolution of the Andes in a transitional zone between flat and normal subduction (33°30′–33°45′S), Argentina and Chile

The sector of the Andes studied in this paper (33°30′–33°45′S) presents a key region to study the relationship between tectonic setting and deformation history in a transitional zone between flat (north of 33°S) and normal (south of 33°45′S) subduction segments. The Andes at these latitudes are primarily composed of the Neogene Aconcagua fold-and-thrust belt and the basement-block uplift of the Cordillera Frontal. Detailed mapping has revealed that the structure within the inner part of the fold-and-thrust belt resulted from both thin- and thick-skinned tectonic interactions. In the outer part, displacement is transferred to Mesozoic décollement levels, accounting for a thin-skinned architecture. Geographically, the switch from thick- to -thin skinned tectonics occurs near the border between Chile and Argentina. gh the geometry of the subducted Nazca Plate may have influenced the timing and style of deformation in the foreland, plate geometry alone does not adequately explain the style of deformation within the fold-and-thrust belt. Here it is shown that the change in deformation style in the fold-and-thrust belt correlates with the location of pre-existing Mesozoic structure, and specifically that Neogene-age thick-skinned thrusting was controlled by the presence of Mesozoic margin-boundary normal faults. Deformation in this region of the Andean fold-and-thrust belt was thus controlled by a combination of tectonic setting and pre-existing extensional structure.