Geological Society of America Special Paper 262 1991 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Geology of the Azua and Enriquillo basins, Dominican Republic; 2, Structure and tectonics Paul Mann zyxwvutsrqponmlkjihgfedcbaZYWVUTSRQPONMLKJIHGFEDCBA Institute for Geophysics, University of Texas at Austin, 8701 Mopac Boulevard, Austin, Texas 78759 P. P. McLaughlin* Department of Geology and Geophysics, Louisiana State Universtiy, Baton Rouge, Louisiana 70803 Calvin Cooper Shell Western E&P, Inc., WCK-4394, P.O. Box 991, Houston, Texas, 77001 ABSTRACT 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 Mio- cene 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 defor- mation, 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 be- tween 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 inden- tation of the south-central margin of Hispaniola by northeastward displacement of the Beata ridge, an aseismic ridge on the Caribbean seafioor. Indentation was accommo- dated 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. 'Present address: Exxon Production Research Company, P.O. Box 2189, Houston, Texas 77252. Mann, P., McLaughlin, P. P., and Cooper, C., 1991, Geology of the Azua and Enriquillo basins, Dominican Republic; 2, Structure and tectonics, in Mann, P., Draper, G., and Lewis, J. F., eds., Geologic and tectonic development of the North America-Caribbean plate boundary in Hispaniola: Boulder, Colorado, Geological Society of America Special Paper 262. 367