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Magnetotelluric image of the Chilean subduction zone in the Salar de Atacama region (23°-24°S): Insights into factors controlling the distribution of volcanic arc magmatism.

2021; Elsevier BV; Volume: 318; Linguagem: Inglês

10.1016/j.pepi.2021.106765

1872-7395

Katarzyna Ślęzak, Daniel Díaz, Jaime Araya Vargas, Darcy Cordell, Felipe Reyes-Cordova, María José Segovia,

Geochemistry and Geologic Mapping

The Salar de Atacama region (23°-24°S) in the Central Andes of northern Chile represents an anomalous segment of the Andes, where a very large forearc basin is present (Salar de Atacama) and the axis of the active volcanic chain is deflected to the east from its regional trend. Here we used magnetotelluric (MT) data to infer the distribution of partial melts and hydrothermal fluids in order to better understand the mechanism controlling the magmatism in this subduction zone. Our 3-D inversion model shows a complex electrical resistivity structure, with several mid crustal conductors ( 1000 Ωm), conductors were imaged below the Precordillera and in the northern SdAb, where major trench-parallel and transverse fault systems are present. We interpret these forearc conductors as evidence of active and fossil hydrothermal systems hosted by the Precordillera Fault System and the Calama-Olacapato-El Toro transverse fault. Conductors found along the arc are spatially coincident with active volcanoes likely representing partial melting in the continental crust. A large conductor was imaged in the backarc, indicating the presence of a significant volume of partial melts below the Altiplano-Puna plateau, as many previous geophysical studies have suggested. The model shows that the mid-lower crust and subcontinental mantle (i.e., >15 km depth) below the SdAb is dominated by resistivity values >100 Ωm., suggesting the presence of a relatively poorly hydrated continental crust and mantle wedge in this segment of the northern Chile subduction zone. These results, together with petrophysical interpretations derived from previous seismic and gravimetric studies, suggest that the lithosphere below the SdAb represents an impermeable block, which inhibits the upward flow of fluids and melts derived from deeper parts of the subduction system. • We present a 3-D electrical resistivity model of Central Andes lithosphere (23°–24°S). • The Salar de Atacama basin (SdAb) lithosphere represents a high-resistivity block. • Petrophysical properties suggest that the SdAb block is an impermeable region. • The SdAb impermeable block may explain the eastward deflection of the volcanic arc.