Abstract

MIRANDA, Silvia; ALCACER, Juan Manuel  and  HERRADA, Alfredo Héctor. 3-D gravimetric moho for the Andean region between the latitudes of 28° S and 33° S. Geoacta [online]. 2016, vol.41, n.2, pp.44-56. ISSN 1852-7744.

The depth to the Moho or crust-mantle interface is usually determined at global or regional scale, using seismic, gravimetric and/or gravimetric-isostatic methods. In general, each of these methods, when they are separately used, produce different results (several tens of kilometers) because they are based on different hypotheses and besides the data are often uneven in terms of type, quality and distribution. These differences could have important implications in the geodynamic analysis of the region under study. Argentina is a country with a limited number of seismic thickness determinations and where crustal and lithospheric features are only partially known. The aim of this study is to improve the crustal model for Argentina through the preparation of Moho models that fit both the seismic and gravimetric data. To this end, gravimetric Moho models have been computed for the Andean region and its foreland between 28° S and 33° S of latitude and 71.5° W and 66.5° W of longitude, an area that covers the San Juan Province and its surroundings. The contours of Moho were obtained by 3-D gravity inversion of a simple crustal layer model. The lower crust-upper mantle density contrast is considered to be constant and equal to 0,42 g/cm³, which is an average value obtained from seismological results and the global model CRUST 1.0. Two Moho models were prepared using alternately as the input: terrestrial gravity data for the Moho model (1), and gravity disturbances provided by the global model of gravity Eigen-6C4 (n= m= 2190) for the model (2). The computed thicknesses were validated using independent depths derived from seismic point data and the crustal global models CRUST 1.0 (seismology) and GEMMA (satellite gravimetry). The gravimetric Moho (1) is the one that shows the best statistics (rms fit) after comparisons with point-wise seismic data. Crustal thickness varies between 74 km and 37 km (54 km mean) with the highest values under the maximum heights of the Andes.

Keywords : Crustal thickness; Gravity; Inversion; Andes.

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