Possibilities of crustal thinning in the Cuyo Basin from the analysis of gravity data.

Abstract

The Cuyo Basin is a part of the Triassic basin set developed in the Andean foreland of Argentina. The origin of this structure has been postulated as being the result of extensional stresses. Crustal thinning is a characteristic structural feature of palaeorifts, although its identification is sometimes obliterated by sedimentary fill and later tectonic events. An analysis of the gravity data of the basin area was undertaken in order to complement the geological interpretation. The gravity effects of the sedimentary fill and the Andean root westward were computed and then removed from the measured gravity anomalies. Seismic velocities and thicknesses were incorporated to compute the gravity effect of the sedimentary fill, and a balanced Airy isostatic model was used to determine the gravity effect of the Andean root. Trend-surface filtering enabled us to establish the existence of gravity highs over the basin. In addition, the isostatic analysis, assuming anti-roots at Moho level under the basin, showed a present state of slight overcompensation indicating that the basin area should subside in future times in order to achieve balance. 2-D gravity modelling of two cross sections of Moho topography at approximately 33° 30' and 35° south. latitude indicates that the Moho is shallower under the basin. From these results a model is proposed which incorporates a slightly thinned crust to justify the present excesses of gravity for the crustal structure of the Cuyo Basin.