Nonlinear inversion of isostatic residual gravity data from Montage Basin, northern Gulf of California

Abstract

The flexural isostatic response to surface loads is used to estimate the crustal thickness in northwestern Mexico and Southwestern USA. This estimate is used to compute an isostatic regional gravity, which, subtracted from Bouguer gravity anomalies, led to the isostatic residual gravity anomaly at Montage Basin. This basin is located between the southern portion of the Mexicali Valley and the northern Gulf of California, it roughly has an extension of [Formula: see text] wide, and it shows a gravity minimum reaching approximately [Formula: see text]. Montage Basin is within the extensional province of the Gulf of California, where rifting is currently an ongoing geologic process, and deep exploratory wells drilled by Petróleos Mexicanos have shown that the basin accommodates thick sedimentary sequences greater than 5 km. The interpretation of the isostatic residual gravity anomaly is considered as a nonlinear inverse problem, constrained using density as a function of depth derived from Gardner’s equation applied to dual time [Formula: see text]-logs, assuming isostatic equilibrium and considering the basin as a subsurface load that is compensated at depth by a mass of unknown shape and density. The outcome of the inverse problem suggests that Montage Basin accommodates as much as 7.5 km thick sedimentary sequences and a compensating mass at a minimum depth of 13 km.