Gravimetric crustal thickness estimation in the Gulf of California

In this study 3D inversion of satellite gravimetric data with 3DINVER.M program is applied to model the depth of the crust in the Gulf of California rift. This rift dextrally separates Baja California Peninsula from the North American continent since Miocene, period in which the change occurred from a fundamentally extensional tectonic regime to the present transtensional. Incipient oceanization occurs in various southern sectors along the rift axis, while to the north the presence of oceanic crust is controversial. As a consequence, the crust of the Gulf marine basin and that of adjacent terrestrial regions exhibit important differences in density and thickness, both fundamental parameters of the method, and therefore, we opted to model independently each domain. The crustal thickness models were compared with previous punctual estimates based on seismic methods, obtaining that 98% of the confronted points of the marine model and 87% of the terrestrial model are adjusted to a range of +/- 6 km difference, with mean differences of 1.5 km and 3.5 km, respectively. In our models, along the Gulf basin axis and from the south to the north evolves from a hyper-thinned crust (similar to 8-12 km), characteristic of oceanic to transitional crust, to a moderately thinned continental crust (similar to 12-18 km). In the surrounding extended area, known as the Gulf Extensional Province, the continental crust usually varies between similar to 15 and similar to 28 km, while on this province flanks the crust reaches similar to 35-40 km in the thickened domains (Sierra Madre Occidental and Colorado Plateau). Based on our estimates of crustal thickness and the regional geology, a new demarcation for the Gulf Extensional Province is proposed.