HR: 1340h
AN: T13C-1475    [Abstracts]
TI: Two-stage Extensional Opening of the Mona Passage as Revealed by New Multibeam Bathymetry and Seismic Reflection Data
AU: * Chaytor, J D
EM: jchaytor@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: ten Brink, U S
EM: utenbrink@usgs.gov
AF: U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA 02543, United States
AB: The Mona Passage, located between Puerto Rico (P.R.) and the Dominican Republic (D.R.), has long been considered a region of significant extensional deformation resulting from the oblique subduction system active along the northern Caribbean plate boundary. Published analyses of GPS data show that extension in this region continues today, with P.R. moving northeasterly away from Hispaniola at a rate of between 3-4 mm/yr, maintaining the active extensional environment between these islands. High-resolution EM 1002 swath bathymetry and multi-channel seismic reflection profiles collected in the Mona Passage in March 2007 and October 2006 respectively have for the first time clearly revealed the nature of extensional deformation within this seismically active region. These new data, combined with data from several recent bathymetry surveys in the region show a complex morphostructural terrane, comprising a mix of fault-, erosional-, and landslide-related morphologies. Flat-lying and northward- and southward-backtilted fault blocks, capped by Oligocene to Holocene aged carbonate units, dominate the seafloor and sub-seafloor landscape. At the seafloor, the fault blocks are in places eroded by the powerful bottom currents passing through the passage, while in the subsurface, they form extensional basins, covered by variable thicknesses of young sediments. The most prominent of these fault blocks is the north-dipping Desecheo Ridge, where as much as 700 m of carbonate and Cretaceous-lower Oligocene volcanic and basement units are exposed on its southern side along the multi-stranded southward- dipping Desecheo Ridge fault. The Desecheo Ridge fault extends from near Punta Higuero on the west coast of P.R. to Desecheo Island, where is steps approximately 1.5 km south and continues westward. Exposed on the seafloor and in the shallow subsurface are two dominant fault sets of differing orientations; a N- to NNW-oriented set and a W- to WNW-oriented set. The N- to NNW-striking faults are typically shorter, deeply eroded, and in many places such as at the southwest corner of Mona Canyon, curve along strike. Faults in the W- to WNW-oriented set, cross-cut the N- to NNW-set and in many places cut the overlying sediment cover, indicating that they are the younger, active faults. To date, no definitive piercing-points or other evidence of lateral or oblique movement have been identified along any of the faults in the passage, suggesting that most if not all of the current motion on these faults may be extensional. The perpendicular direction to the active fault set (NNE-SSW), while similar to the relative motion between the eastern D.R. and western P.R. given from GPS, is at odds with the E-W extension direction implied by the Mona Rift. Several of the long E-W striking faults extend along much of the approximately 125 km width of the passage, some of which appear to be continuations of sub-aerially exposed faults identified in western P.R., such as Cerro Goden and Mayaguez faults. The length of these faults and the presence of other major, and likely active, faults in close proximity to the coasts of P.R. and the D.R., make an understanding of these individual faults and wider structural fabric of the region important for seismic hazard analysis. In terms of the tectonic history of the region, the presence of two distinct fault orientations of differing ages in the passage may reflect a moderate shift in plate motion during the current stage of extensional opening or a record of the current and an earlier (Miocene-Pliocene?) stage of deformation.
DE: 3025 Marine seismics (0935, 7294)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
SC: Tectonophysics [T]
MN: 2007 Fall Meeting