Magnetotelluric data were collected in the late 1990s in the Central Andes of
Chile and Bolivia, with the aim to delineate the electrical conductivity
distribution in the subsurface and its relations to subduction processes. In
previous studies, these data were interpreted based on 2-D models. The
principal result was a vast conductivity zone beneath the Altiplano high
plateau at mid and lower crustal depths and a much smaller, though significant
conductor associated with the Precordillera Fault System. However, there are
some significant 3-D effects in the investigation area, in particular near the
coast and on the eastern Altiplano. The aim of this work is to give a
reinterpretation based on new 3-D inversion of these data. The 3-D inversion
not only provides a better fit to the data compared to 2-D results but
furthermore allows to include sites with strong telluric distortion which were
ignored in previous studies. We are now able to explain anomalous phases above
90° and induction arrows pointing subparallel to the coast as observed at
several sites in the Coastal Cordillera. These strongly distorted data are
caused by highly conductive near-surface structures that are partly connected
to the Pacific Ocean, forcing currents to flow around the sites. The lower
crust beneath the Coastal Cordillera resembles a poorly conductive, nearly
homogeneous half-space and is electrically unremarkable. Besides, we can now
image the Precordillera conductor as a continuous, elongated feature. The
volcanic arc of the Western Cordillera is highly resistive with the exception
of a few conductive spots which may be associated with certain individual
volcanoes or geothermal resources, respectively. The Altiplano conductor is
again the dominant electrical feature in the Central Andes, indicating
widespread melting of the middle and lower back-arc crust