CRUSTAL DISCONTINUITY IMAGE ACROSS SOUTHERN COLIMA GRABEN FROM MAGNETOTELLURICS, SEISMICITY AND GRAVITY DATA

The Colima Graben (CG) is considered as the SW limit of the Jalisco Block (JB), where the Rivera and Cocos plates coincide along a diffuse nearly NS frontier also known as the Colima rift. It is a documented extensional region where the differences in subduction slab angles of the micro-Rivera and Cocos plates force an anisotropic ascent of upper mantle material and mixed hydrothermal fluids, reaching the surface trough fractured rocks following deep rooting faults. The presence of widespread mantle derived magmas at the surface and the abundant shallow seismicity are evidence of this tectonically active extensional zone, where large earthquakes have occurred. Being a volcanic hazard the Colima volcanic complex region is also regarded an important reserve of geothermal energy.

Here we present a resistivity image across the southern portion of the Colima graben with the aim of adding clues about the main fractured paths and deep faults based upon conductivity anomaly distribution, constrained by natural micro-seismicity and high gradient gravity zones. A high conductivity anomaly coinciding with the western edge of the Colima graben is correlated with a prominent gravity low and intense micro seismic activity. The combined anomalous conductivity and active micro-seismicity support the hypothesis of a fragmented subducting slab under the Colima graben extending at lower crustal depths.