Crustal structure and Curie point depth in central Mexico inferred from the spectral analysis and forward modeling of potential field data

Abstract

Different interpretations of crustal thickness variations have been proposed for central Mexico. The studied region encompass the transition between the Mesa Central, an elevated plateau with low relief, and the Sierra Madre Oriental, a late Mesozoic–early Cenozoic fold-thrust belt at lower mean elevation. Crustal models discussed here are based on three different published hypotheses: 1. Homogenous crustal thickness and a flat Moho beneath both provinces; 2. Thicker crust beneath the Mesa Central compared to thinner crust under the Sierra Madre Oriental; and 3. Thinner crust below the plateau and thicker crust beneath the fold-thrust belt. This last configuration implies the presence of lower-density mantle under the plateau to produce the higher mean elevation. We tested these conflicting configurations using gravity and magnetic data to produce forward models of the previously published interpretations and to obtain new crustal thickness and Curie point depth estimates. Our results show significantly higher error for model 1 and similar errors for models 2 and 3, ruling out model 1 but preventing discrimination between models 2 and 3 through forward modeling. However, the geothermal state results along with our depth-to-Moho estimates indicate the presence of a wide region beneath the eastern portion of the Mesa Central with thicker (40–52 km) and colder (−35 to −45 mWm−2) crust as compared to thinner crust (34 to <40 km) with elevated heat flow values (−50 to −85 mWm−2) beneath the portion of the Sierra Madre Oriental in the study area. Broad negative isostatic anomalies in the Mesa Central are evidence for excess mass/density under the plateau. Our findings are more consistent with model 2 and incompatible with model 3, in which the presence of shallow asthenosphere and partial melt under the plateau implies lower density rocks beneath the plateau and a corresponding steeper geothermal gradient.