| Combined Radar and GLORIA Mosaics of Puerto Rico,
the U.S Virgin Islands, and Surrounding Deep Ocean Areas: Tectonic Interpretations
Scanlon, Kathryn, M., U.S. Geological Survey, Woods
Hole, Ma 02543 Southworth, C. Scott., U.S. Geological Survey, Reston, VA 22092 modified from 12th Caribbean Geological Conference, 1989. (abs) St Croix, USVI The first high-resolution, geometrically controlled side-looking airborne radar (SLAR) mosaic of Puerto Rico and the U.S. Virgin Islands (USVI’s) has been combined with the GLORIA long-range sidescan sonar mosaic of the surrounding deep ocean area to provide a unique view of a section of the northern Caribbean plate boundary zone. The GLORIA data provide a reconnaissance view of the structural and bathymetric features of the sea floor; the SLAR data penetrate the persistent cloud cover and dense vegetation that obscure aerial views of the geologic structures and physiographic terrains of the islands. The controlled mosaics allow is to map structures across the land-sea boundary and to infer correlations between geomorphic features on land and in the submarine environment.Puerto Rico and the USVI’s lie within a 400-km-wide plate boundary
zone between the Caribbean plate and the North American plate. The sense of motion between
the two plates is now mainly left-lateral strike-slip, although north-south convergence
and active subduction occurred here until about Eocene time. The northern extent of this
plate boundary zone is defined by the Puerto Rico Trench. Its sediment-covered floor is
clearly visible in the GLORIA mosaic, as are several long, slightly sinuous,
east-trending, strike slip faults. These faults lie in the forearc region between the
baser of the northern insular slope and the trench floor and presumably accommodate much
of the preset-day plate motion. The radar mosaic of the Cretaceous and early Tertiary
crystalline core of Puerto Rico exhibits lineaments trending approximately N72W. These
lineaments are not discernible in the middle and late Tertiary sedimentary units that
flank the older core, which implies that they are relics of the older convergent regime
rather than of the more recent strike-slip regime. The Great Southern Fault trends
somewhat more north of west (N55W) than the other lineaments, which it appears to
truncate. This suggests that the fault postdates the other lineaments. The GLORIA mosaic
of the Mona Canyon area shows fault traces that have the same orientation as the Great
Southern Fault. The southern edge of the plate boundary zone is marked by the Muertos
Trough, where the GLORIA mosaic reveals a band of deformed sediments at the base of the
insular slope. |