HR: 15:40h
AB: Along the convergent Pacific margin of Costa Rica and Nicaragua, subduction of the ocean plate sediment and tectonic erosion of the continent are the currently dominant processes. Multibeam bathymetry shows a range of young morphotectonic structures in the continental slope that vary along the margin paralleling morphological changes in the subducting plate. The distribution and nature of structures can be interpreted in relation to subduction erosion at the front and base of the continent. Off south Costa Rica subduction of thick crust of Cocos Ridge has produced the greatest erosional retreat of the margin. Off central Costa Rica subduction of large ridges and seamounts grouped in chains breach the margin front and leave grooves in the slope indicating material removal at the base of the plate. Where the ocean plate lacks numerous large seamounts flexural normal faulting controls the roughness of seafloor topograpy. Where little faulted ocean plate subducts (e.g. off NW Costa Rica) the continental slope displays the most stable morphology, with gentle dips and well developed canyon systems in the upper-middle slope. Where the ocean plate is pervasively faulted (e.g. off Nicaragua) the continental slope exhibits a less stable morphology. The lower slope displays "en echelon" ridges mimiking subducting topography. In a steep middle slope, slump scars penetrate sediment 100s of meters. A gentler upper slope locally displays canyon systems. Where subduction of large seamounts has not recently sculptured the margin a pervasive system of fractures, hundreds of meters to 4 km long, runs along the middle slope. Seismic images indicate that the fractures are associated with normal faulting in slope sediment. Some of the faults penetrate the continental framework rock to great depths. Normal faulting is produced by collapse of the upper plate due to basal erosion. Along the area of faulting conical structures a few hundred meters wide and up to 200 meters high occur. Observations with a TV-camera over one of them indicates a mud volcano. These features may be related to deep penetrating normal faults that focus flow of fluids originating at the plate boundary.
AN: T12D-08
TI: Mass Transfer and Fluid Flow Paths Related to Subduction Erosion at the Middle America Convergent Margin
AU: * Ranero, C R
EM: cranero@geomar.de
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: von Huene, R
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Weinrebe, W
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: McIntosh, K
AF: UTIG, 4412 Spicewood Spring Rd., Austin, TX 78759 United States
AU: Reichert, C
AF: BGR, Stilleweg 2, Hannover, 30655 Germany
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
DE: 3025 Marine seismics (0935)
DE: 3045 Seafloor morphology and bottom photography
SC: T
MN: Fall Meeting 2000