Crustal structure on west-central Baja California peninsula, México, inferred by 3D linear inverse modeling of gravity data

Abstract

Gravity data from the west-central portion of the Baja California Peninsula, in NW Mexico, were processed on the ellipsoidal reference frame to obtain isostatic residual gravity anomalies. This is a nearly flat region close to sea level and blanked by sediments, where a gravity high bounded by two prominent minima occurs. The gravity high is oriented in a NE-SW direction, and it is possibly the most prominent gravity anomaly transverse to the Baja California Peninsula. The gravity minima, located towards the NW and SE from the gravity high, are respectively related with the Sebastián Vizcaíno and Purísima sedimentary basins. These basins were developed since Early Cretaceous times during the subduction of the Farallon Plate under the North American plate. To infer the crustal structure and the basement geometry in this region, inverse linear modeling is carried on a multilevel data set of upward continued isostatic residual gravity data. Assuming that compaction is the primary diagenetic process on the sediments filling the basins, the initial model is constrained by the surface geology expressed as a density contrast that decreases with depth. The outcome of the inversion is density contrast in a cuboid model, constituted by 67,379 prisms, and its three-dimensional representation suggests that these two basins accommodate as much as five km-thick sedimentary sequences –formed by shallow siliciclastic and deep volcaniclastic rocks penetrated by wells drilled in the region– lying above the inferred basement, which shallows beneath the Lagunitas gravity high, consistently with depth to crystalline rocks penetrated by wells.