Structure of the southern Jalisco subduction zone, Mexico, as inferred from gravity and seismicity

Abstract

A type-model of the geological structure of the Jalisco subduction zone was determined by matching gravity anomalies observed along a profile perpendicular to the Jalisco coast near Barra de Navidad with the gravitational attraction of a geologic cross section constrained by seismicity data. The thickness of the continental crust of the Jalisco block averages ~38 km, and gradually thickens eastward reaching a maximum thickness of 44 km. The density of the upper part of the subducting lithosphere increases at a depth of ~30 km, perhaps reflecting a phase transition of basalt to eclogite as has been proposed for the Chile subduction zone. The upper mantle west of the trench exhibits lower densities relative to the rest of the upper mantle. This low density zone is thickest near the East Pacific Rise and thins eastward towards the Middle America Trench, and may reflect a broad zone of magma emplacement along the East Pacific Rise, similar to that observed at the East Pacific Rise at 16ES.