The regional structure of south-central Hispaniola is dominated by synclinal Upper Miocene to Recent sedimentary ramp basins separated by fault-bounded anticlinal mountain ranges. Major folds nested in the larger scale ramp basins affect Upper Miocene to Pleistocene sedimentary rocks and have fold axes ranging in trend from northwest-southeast to east-west. These folds are parallel in profile, lack internal deformation, and formed during progressive closure of the ramp basin in post-Early Pliocene time. A shortening amount of 12 percent is estimated for concentric folds in the Azua basin using a regional cross section. The orientations and the sense of slip on major and minor faults are consistent with major fold data and indicate a northeast-southwest- or north-south-directed regional shortening.

Sedimentologic and paleontologic data indicate that the large-scale ramp basin structure of south-central Hispaniola began to form in Late Miocene time. The synclinal structure of the San Juan-Azua ramp basin acted to confine a large clastic submarine fan that prograded southward from the area of the present-day Cordillera Central in late Miocene to middle Pliocene time (McLaughlin and others, this volume).

We interpret Late Miocene-Recent ramp basin formation and uplift in south-central Hispaniola as a response to oblique collision and continued convergence between an oceanic plateau terrane in southern Hispaniola and previously assembled island-arc terranes in central and northern Hispaniola. Miocene suturing of the two areas converted a previous strike-slip margin across south-central Hispaniola into a strike-slip restraining bend that is presently active.

The regional pattern of faulting and folding suggests late Pliocene to Recent indentation of the south-central margin of Hispaniola by northeastward displacement of the Beata ridge, an aseismic ridge on the Caribbean seafioor. Indentation was accommodated by strike-slip faults of opposite sense bounding the 50-km-wide indented region.

Increased northeast-southwest shortening of sedimentary rocks in the eastern Enriquillo and Azua basins, produced large-scale curvature and rotation of fold axes in the indented area, and perhaps localized extension and basaltic volcanism. The Miocene to Recent collisional zone in south-central Hispaniola forms a contact zone between two microplates embedded within the North America-Caribbean plate boundary zone.