Present-Day Caribbean-North American Oblique Convergence Through the Ocoa-Bonao-La Guacara Fault Zone, Southern Central Hispaniola: A Transition Zone Between Oceanic Subduction and Arc-Oceanic Plateau Collision

Abstract

According to GPS measurements, the Caribbean plate is moving east-northeastward relative to the North American plate at a rate of ∼20 mm/a. This oblique motion is partly accommodated in southern Hispaniola by northward underthrusting/subduction bellow the Muertos submerged accretionary prism and the Peralta fold-and-thrust belt. This work investigates the active transition zone that connects Muertos and Peralta: the Ocoa-Bonao-La Guacara fault zone (OBFZ). Combined detailed structural analysis at macroscopic and mesoscopic scales, regional magnetic data and seismicity analysis, geomorphic observations, fault-slip data inversion and geochronology of Quaternary deposits allow to establish the deformation pattern for the OBFZ along southern central Hispaniola. Distinct tectonic regimes have occurred successively in the Neogene, within a consistent regional NE-trending horizontal shortening: (a) a lower Miocene to Early Pleistocene D1 regime characterized by SW-directed thrusting that homogeneously affects the region; and (b) an Early/Middle Pleistocene to Holocene D2 regime of strike-slip to transpressional faulting mainly located along the OBFZ. The change is coeval with the tectonic indentation of the Beata Ridge in the back-arc region of the Hispaniola microplate. Finally, a Late Pleistocene to Holocene D3 extensional regime has a local development around the Ocoa Bay. Part of the present-day stress-field induced by the Beata Ridge collision is accommodated by the OBFZ within the Hispaniola microplate. This fault zone defines the onland transition between oceanic subduction and arc-oceanic plateau collision. Due to its length and potential to generate large earthquakes, the OBFZ must be considered in the regional seismic hazard assessment.