Three-Dimensional Geometry of the Upper-Crust in the Mexicali Spreading Center and Consequences on the Cerro Prieto Geothermal Area

Abstract

We interpreted the gravity data of the Laguna Salada and Mexicali Valley, getting the three-dimensional density model for those areas. We determined the 3D geometry of the interphase between sediments-metasediments and the upper-crust (granites). Top upper-crust geometry was determined by quadratic programming inversion constrained by hard information like borehole and 2D seismic cross-sections. We used an algorithm that considers layers like a geological formation. The inversion purpose is to find the top and bottom topography for every formation constrained by hard information. We found that sediments layer in the Mexicali Valley is as thickness as 7 km and we needed a lineal compaction function in order to agree with the seismic information. Same happens in the Laguna Salada Valley, but the compaction function was different because depth is lower that Mexicali Valley. The upper-crust top topography shows a very big depression along the Cerro Prieto faults that was reported before as the Montague basin. The basin shape runs along the Colorado River until the shore line. Meaning that the river caused this sinking in the upper-crust. In the pull-apart basin we see a depression in the upper-crust, meaning that subduction can be the cause. We also see that pull-apart basin is a little bit larger than expected. Cerro Prieto Geothermal area is located inside the pull-apart basin. To know the geometry of this basin is important for future reservoir exploration plans.