Motion of Caribbean Plate during last 7 million years and implications for earlier Cenozoic movements

Abstract

The direction and rate of movement of the Caribbean plate with respect to North America are determined from the slip vectors of shallow earthquakes and from the configuration of downgoing seismic zones in the Greater and Lesser Antilles. A calibration of the relative plate motion for the northeastern Caribbean using data from other subduction zones indicates an average rate of 3.7±0.5 cm/yr for the past 7 million years (Ma). The direction of plate motion inferred from focal mechanisms (ENE) is nearly the same as that deduced from the configuration of downgoing seismic zones going around the major bend in the arc. With respect to North America, the Caribbean plate is moving at an angular velocity of 0.36°/Ma about a center of rotation near 66°N, 132°W. Vector addition using those data and that for the relative motion of North and South America indicates that the Caribbean is moving at an angular velocity of 0.47°/Ma about a center of rotation near 60°N, 88°W with respect to South America. The presence of intermediate‐depth earthquakes beneath Puerto Rico and the Virgin Islands is ascribed to the curvature of the plate boundary and a component of underthrusting that has been going on for at least the past 7 Ma and is likely occurring today. The alternative hypothesis that earthquakes beneath those areas are occurring in materials that were subducted during the Eocene, the last major episode of magmatism, is not tenable from thermal considerations. The lack of recent magmatism in the eastern Greater Antilles is ascribed to the relatively small component of underthrusting. The 2 cm/yr rate of seafloor creation along the mid‐Cayman spreading center for the past 2.4 Ma does not appear to reflect the total Caribbean‐North American plate motion while the 4 cm/yr spreading rate from 6.0 to 2.4 Ma does. Between the mid‐Cayman spreading center and eastern Guatemala, the northern boundary of the Caribbean plate is narrow and follows the southern margin of the Cayman trough. Seismic activity between the spreading center and eastern Hispaniola, however, occurs over a zone about 250 km wide that extends from Cuba to Jamaica and across the entire width of Hispaniola. Individual faults within this broad plate boundary appear to have accommodated differing amounts of motion as a function of geological time while the cumulative plate motion across the zone remained nearly constant. The percentage of total plate motion accommodated near southern Hispaniola and Jamaica is inferred to have increased about 2.4 Ma ago. That change may have been caused by the collision of parts of the Bahama bank and northern Hispaniola. This explanation for the sudden decrease in seafloor creation along the mid‐Cayman spreading center is less catastrophist than the hypothesis that the entire Caribbean plate suddenly changed its velocity with respect to surrounding plates. The Caribbean plate may be regarded as a small buffer plate whose motion is now governed by the movement of the larger North and South American plates which bound it on three sides. The Caribbean plate is either at rest or moving eastward at a rate of no more than 1 cm/yr in the hot spot reference frame. Since the relative motion of the larger plates surrounding the Caribbean has been nearly constant for the last 38 Ma (anomaly 13 time) and since the forces on the Caribbean plate do not appear to have changed greatly during that interval, we extrapolate the motion of the last 7 Ma back to 38 Ma. A reconstruction for the late Eocene places the Caribbean plate about 1400 km west of its present position. The faster rate of plate motion we calculate makes it more likely that the lithosphere beneath the basins of the Caribbean originated in the Pacific. It also has implications for the seismic potential of the region, paleocirculation in the Atlantic Ocean and origin of sediments in the area. Our late Eocene reconstruction aligns the eastern continental margin of Yucatan with that along the southeast side of the Nicaragua rise. This 2500‐km‐long feature may have acted as an arc‐arc transform fault from the late Mesozoic to the late Eocene. Arc‐related rocks of those ages in the Greater Antilles and northern Lesser Antilles define a northwesterly trending subduction zone along the northeastern edge of the former East Pacific‐Caribbean plate. At least three fragments of anomalous seafloor have been sutured onto Hispaniola in the past 50 Ma.