DEEP-CRUSTAL STRUCTURE OF CENTRAL MEXICO DERIVED FROM INTERPRETATION OF BOUGUER GRAVITY-ANOMALY DATA

Quantitative modelling of the Bouguer gravity anomaly map for central Mexico and of three long (approximately 400 km) north-south gravity profiles has been uss to investigate the crustal and upper mantle structure beneath central and southern Mexico. The crustal thickness increases from the Pacific ocean margin towards the continental interior, presenting maximum values beneath the Trans-Mexican volcanic belt (average thickness of approximately 40 km), particularly beneath the central-eastern part of the belt. The TMVB appears to be under regional isostatic equilibrium with local isostatic anomalies. The crustal models suggest the presence of a low density layer at the base of the crust which may be responsible for the uplift mechanism of the volcanic-capped central plateau. This interpretation agrees with geothermal models constructed from travel time analysis of Rayleigh and Love waves for central Mexico. Subduction of relatively young Cocos plate lithosphere may have resulted in shallow subduction dip angles and a high geothermal regime beneath the TMVB, causing thermal expansion, partial melting of mantle material, and then regional plateau uplift and volcanism.