CONICET | Buscador de Institutos y Recursos Humanos

The southern Puna plateau is a conspicuous example of a high-elevation orogenic plateau in a non-collisionalsetting. This orogenic sector is currently located above an anomalously shallow subduction segment, in whichtiming and relation to upper-plate tectonics have been widely overlooked. This subduction segment, here referred to as the southern Puna shallow subduction (SPSS), is characterized by a ~200 km wide shallow arealocated at ~300 km from the trench at a depth of ~100?120 km and dipping 10?12° to the east. To determinethe onset of the SPSS and its link to the tectonic and magmatic activity in this region, we analyzed the tectonomagmatic record of the southern Puna plateau from preexisting datasets. Also, we present a new approachbased on global subduction data that provides a straightforward methodology to extract potential paleo-slabangles from the bedrock arc record. This analysis reveals that a pronounced eastward arc-front migration andmagmatic broadening took place at ~26 Ma and was preceded by ~4 Ma of reduced magmatic activity, whichwe link to the inception of the SPSS. As expected in shallow subduction settings, a change to basement-coreddistributed deformation south of 25°S in the southern Puna plateau coincides with the beginning of shallowsubduction. Also, the SPSS is coincident with the enigmatic post-Eocene intraplate deformation of the OtumpaHills located at ~950 km from the trench. We suggest that this succession of events is not fortuitous and that thedevelopment of the SPSS impacted directly the overriding plate since the Oligocene contributing to the buildingof one of the largest topographies (> 3 km) and thickest orogenic crusts (~70?60 km) on Earth. The shallowsubduction would have acted jointly with Cenozoic changes in plate kinematics and climate enhancing Andeanorogenesis at studied latitudes.

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