HR: 14:05h
AB: An extensive seismic study of the Nicaragua Pacific margin, using the large seismic array on the R/V Ewing, imaged back-rotated normal fault blocks in the trench and its seaward wall. Such faults can be resolved beneath the margin wedge at least 20 km landward of the trench. Fault block orientations mapped with Hydrosweep bathymetry remain unchanged across the trench to the lower continental slope, indicating a clear influence of the incoming plate on upper plate structure. A thin sedimentary apron overlies a high amplitude reflection on the continental slope, similar to that seen off Costa Rica. Dredging where the deeper rocks crop out yielded olivine basalts, basaltic sandstone, limestone and chert. Most of the rocks are tectonized, indicated by macroscopic faults and by fractured grains and undulose extinction in thin section. The limestone contains Late Cretaceous nannofossils, and limestones of this age onshore overlie Nicoya complex basalts, cherts and volcaniclastics. This dredge represents the first recovery of basement on the continental slope off either Nicaragua or Costa Rica. Reflections suggest that this basement complex may continue to within a few hundred meters of the trench axis, thus indicating no frontal accretion and possible tectonic erosion.
AN: T12D-03 INVITED
TI: Influence of Lower Plate Structure on the Overriding Slope Offshore Nicaragua: New Geophysical Observations and the First Dredge Samples of Basement Rocks
AU: * Silver, E A
EM: esilver@es.ucsc.edu
AF: Earth Sciences Department, University of California at Santa Cruz, Santa Cruz, CA 95064 United States
AU: McIntosh, K D
EM: kirk@utig.ig.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Ranero, C
EM: cranero@geomar.de
AF: GEOMAR, Wischhofstr 1-3, Kiel, 24148 Germany
AU: Ahmed, I
EM: ahmed@ig.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Jiao, J
EM: junru@mail.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Johnson, K
EM: kevin@ig.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Meckel, T
EM: tip@mail.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78759-8500 United States
AU: Walter, C
EM: cwalter@geomar.de
AF: GEOMAR, Wischhofstr 1-3, Kiel, 24148 Germany
AU: Berhorst, A
EM: aberhorst@geomar.de
AF: GEOMAR, Wischhofstr 1-3, Kiel, 24148 Germany
AU: Guzman, C
EM: carlos_guzman.gf@ineter.gob.ni
AF: INETER, Aptdo 2110, Managua, Nicaragua
AU: Kelly, R
EM: rkelly@whoi.edu
AF: Dept. of Geology and Geophysics, Woods Hole Oceanographic Inst, Woods Hole, MA 02543 United States
AU: Kling, S A
EM: skling@gs.ucsd.edu
AF: Consulting Micropaleontology, 416 Shore View Lane, Leucadia, CA 92024 United States
AU: Ramirez, T
EM: tramirez@es.ucsc.edu
AF: Earth Sciences Department, University of California at Santa Cruz, Santa Cruz, CA 95064 United States
AU: Taylor, B
EM: btaylor@lgc.com
AF: Landmark Graphics Corp., PO Box 9126, Englewood, CO 80111 United States
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: T
MN: Fall Meeting 2000