The N-S Extension of The Mexico Basin: Is Confirmed by Gravity Analysis

Abstract

The Mexico Basin is in the eastern portion of the Trans-Mexican Volcanic Belt, where it is repeatedly affected by strong ground motions. Notwithstanding, the tectonic setting of this region is not adequately defined, and several efforts are underway to improve its characterization. Here we use a high-resolution (220 m), satellite-derived gravity data set to acquire the matching Bouguer anomaly, from which 3D inversions are performed at varying resolutions, to obtain density distributions to depths of up to 15 km. The gravity signature agrees with an N-S extensional process previously recognized, based on geological arguments. Two gravity saddle points are identified flanking a minimum in the S portion of the basin; immediately southward is located Sierra del Chichináutzin, which we interpret as resulting from the N-S extensional process. Two relevant, not previously reported gravity anomalies are identified: the Ajusco Gravity Anomaly (AGA) and the Central Gravity Anomaly (CGA), the former associated with Ajusco volcano, and the latter with the central portion of Mexico City. The AGA contains two polygenetic structures: Ajusco volcano and San Miguel volcano; given their proximity to the Mexico and Toluca basins, a detailed exploration of their density distributions is performed. A comparison is made with seismic results reported elsewhere, between density and seismic velocity, finding good matches to depths up to 10 km below sea level.