To More Links on Caribbean Research

Abstract submitted to the 1999 AGU Spring Meeting. For more information, please check out the Canape GPS Project.

Microplate Tectonics Along the North American-Caribbean Plate Boundary: GPS Geodetic Constraints on Rigidity of the Puerto Rico-Northern Virgin Islands (PRVI) Block, Convergence Across the Muertos Trough, and Extension in the Mona Canyon

1, P. Jansma^{1, 2}, E. Calais², C. DeMets³, T. Dixon⁴, P. Mann⁵, G. Mattioli^{1, 2}

¹Department of Geology, University of Puerto Rico, Mayaguez, PR 00681 USA
²Geosciences Azur, CNRS, Sophia Antipolis, France
³Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706 USA
⁴Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL 33149 USA
⁵Institute for Geophysics, University of Texas, Austin, TX 78759 USA

Puerto Rico and the northern Virgin Islands lie within the broad boundary zone between the North American and Caribbean plates. Seismicity and marine geophysical survey data from active onshore and offshore faults have been interpreted by earlier workers to indicate that at least two, and possibly three, microplates occupy the diffuse boundary zone: 1) the Gonave microplate; 2) the Hispaniola platelet, which may consist of several smaller terranes; and 3) the Puerto Rico-northern Virgin Islands block (PRVI). PRVI is defined by the Puerto Rico trench on the north, the Muertos Trough on the south, the Mona Canyon fracture zone on the west, and the Virgin Islands-Whiting Basin and the Anegada Passage on the southeast and east. Most earthquakes are concentrated along these structures, implying a rigid PRVI. We discuss results from GPS geodetic measurements acquired in PRVI since 1994 to constrain PRVI neotectonics. GPS-derived velocities are analyzed with respect to both stable North American and Caribbean reference-frames and compared with GPS-derived velocities for eastern Hispaniola. GPS geodetic data from CANAPE (CAribbean-North American Plate Experiment) constrain motion of the Caribbean relative to North America as $\sim$ 20 mm/yr toward the ENE. Velocities of sites within PRVI agree within error in both rate and azimuth and are 3-5 mm/yr in a westward direction relative to the stable Caribbean plate. At the level of a few millimeters per year, these data are consistent with a rigid PRVI and limited convergence across the Muertos Trough, implying that most North American-Caribbean plate motion is accommodated along the Puerto Rico Trench and/or offshore faults north of the island. The data do not require rigid-body rotation of PRVI. Comparison of site velocities in PRVI with those in eastern Hispaniola constrains the tectonic setting of the Mona Canyon. GPS-derived velocities of eastern Hispaniola relative to the Caribbean plate are considerably faster than those of PRVI and trend toward the SW, yielding left-oblique opening across the NS-trending Mona Canyon.