Tears, windows, and signature of transform margins on slabs. Images of the Cocos plate fragmentation beneath the Tehuantepec isthmus (Mexico) using Enhanced Seismic Models

Abstract

In southern Mexico, tears of the Cocos plate, slab windows, and signatures of the transform margins have been invoked to justify the peculiar geometry of the subducting plate and the volcanism of the region.In this work the first seismic velocity models of the Tehuantepec subduction zone using the Enhanced Seismic Tomography (EST) method allowed to reconstruct the geometry of the slab and surroundings of this complex sector of Mexico. EST is applied to a dataset of 6370 events occurred in the region during the last twenty years and recorded by 38 stations deployed onshore by the Mexican National Seismological Service (SSN). Data and method allowed to generate 3D models of the P wave velocities and P-to-S ratio with a resolution able to elucidate the important role of the Tehuantepec Ridge on the origin of a vertical propagating tear that controls the magmatism of the El Chichón volcano as well as to identify the presence of lateral bending, windows, tears, and incipient fragmentation in the first 200–250 km of the subducted plate. All these findings allowed to propose and updated view of the oceanic and continental lithosphere opening the discussion on the role of these features on the geodynamics and tectonics of the region.