Structure of the Cerro Prieto Pull-apart basin from joint inversion of gravity, magnetic and magnetotelluric data

Abstract

The large transform fault system that separates the Pacific and the North American plates in the Gulf of California is conformed by a system of oblique rifts and large dextral transform faults. Besides their seismogenic importance, several of these structures are related to geothermal resources in the area. This system originates the Cerro Prieto Pull-apart basin (CPPAB), which is particularly important as it hosts the world's third largest geothermal field. It is remarkable that, despite intensive geological and geophysical exploration in the CPPAB, there is no published geophysical image of the basin that gives clear evidence of the underlying basement and the existence of an active pull-apart basin and whether it may be the source of heat of the reservoir. We posit that the joint inversion of multiple geophysical data can unveil the underlying CPPAB structure. We then applied the cross-gradient joint inversion to recently collected gravity, magnetic and magnetotelluric data on three intersecting profiles. From the joint models, we could clearly distinguish the major geometry of the basin and classify the basement units by their characteristic geophysical signatures, as well as propose the occurrence of various suites of intrusives. The interpreted models correlate well with surface geology and geophysical maps and depict a likely structure for the active pull apart basin in the area.