Deep structural setting of the North Caribbean plate boundary in eastern Guatemala

Two-dimensional inverse gravity modeling is presented to help determine the deep structural framework of the left-lateral Polochic-Motagua fault systems; They represent a major segment of the North American-Cari-bbean plate boundary. These seismically active tectonic lineaments, crossing broadly E-W Guatemala, are super¬imposed over a narrow suture where slices of ophiolitic assemblages crop out. Within the principal displacement zone of the fault systems, pull-apart basins and restraining zones (push-up) were formed. A fault population analysis along the strike of both fault systems in the Izabal and Motagua valleys, combined with satellite-de¬rived data, have allowed determining the gross geometry and kinematics of the transform systems. Geological information and commercial seismic data were used to constrain the shallow geometry and structure of the plate boundary across a 60-km-long cross-section located to the east of Lago Izabal, the largest pull-apart basin formed along the Polochic transform system, and across the Motagua valley. The inverse gravity model fits the complete Bouguer anomaly map of the area and explains most of the observed long-wavelength anomalies, as well as the local anomalies associated with intracrustal and shallow crustal geological bodies. The main features derived from the integrated geophysical-geological approach are the geometry and depth of sedimentary basins associ¬ated with the transform systems, and the root of the ophiolitic bodies in the suture zone.