A magnetotelluric study in the Southern Chilean Andes

Long-period magnetotelluric investigations were carried out along two transects traversing the Southern Chilean Andes from the Pacific Ocean until the Argentinian border near latitude 39 degreesS to study the mid- and deep-crustal distribution of electrical conductivity. Dimensionality analysis showed that the MT data may be regarded as 2-D with the exception of areas in the Longitudinal Valley and the region east of the volcanic chain; a subsequent multi-site decomposition of magnetotelluric impedances yielded approx. N-S regional strike directions for most parts of the two profiles. First 2-D inversion revealed a zone of moderately high conductivities (approx. 0.1 S/m) in the deep crust below the active volcanic arc, extending eastwards to the Argentinian border. Inversion results of both profiles are very similar, except of a good mid-crustal conductor in the Longitudinal Valley, which only appears in the north and may image a fault zone running obliquely to the main South Andean structures.