Present-day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike-slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE-directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre-Early Pleistocene D1 event of NE-trending compression, which gave rise to the large-scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan-Azua basin. This was followed by a near pure strike-slip D2 stress regime, partitioned into the N-S to NE-SW transverse Ocoa-Bonao-La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub-parallel deformation corridors. Shift to D2 strike-slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard.
Located in northern Dominican Republic, the Early Cretaceous Rio Boba mafic-ultramafic plutonic sequence constitutes a lower crust section of the Caribbean island arc, made up by gabbroic rocks and subordinate pyroxenite. Modal compositions, mineral chemistry, whole-rock compositions and thermobarometric calculations indicate that pyroxenites and gabbronorites represent a cumulate sequence formed by fractionation of tholeiitic magmas with initially very low H2O content in the lower crust of the arc (0.6-0.8 GPa). Melts evolved along a simplified crystallization sequence of olivine ® pyroxenes ® plagioclase ® Fe-Ti oxides. The magmatic evolution of the Rio Boba sequence and associated supra-crustal Puerca Gorda metavolcanic rocks is multi-stage and involves the generation of magmas from melting of different sources in a supra-subduction zone setting. The first stage included the formation of a highly depleted substrate as result of decompressional melting of a refractory mantle source, represented by a cumulate sequence of LREE-depleted IAT and boninitic gabbronorites and pyroxenites. The second stage involved volumetrically subordinate cumulate troctolites and gabbros, which are not penetratively deformed. The mantle source was refractory and enriched by a LILE-rich hydrous fluid derived from a subducting slab and/or overlying sediments, and possibly by a LREE-rich melt. The third stage is recorded in the upper crust of the arc by the Puerca Gorda ‘normal’ IAT protoliths, which are derived from an N-MORB mantle source enriched with a strong subduction component. This magmatic evolution has implications for unravelling the processes responsible for subduction initiation and subsequent building of the Caribbean island arc.