HR: 0800h
AN: T11B-0384    [Abstracts]
TI: Detailed Seismic Reflection Images of the Central American Volcanic Arc
AU: * McIntosh, K D
EM: kirk@ig.utexas.edu
AF: University of Texas at Austin Institute for Geophysics, 4412 Spicewood Sprgs. Rd. Bldg.600, Austin, TX 78759 United States
AU: Fulthorpe, C S
EM: craig@ig.utexas.edu
AF: University of Texas at Austin Institute for Geophysics, 4412 Spicewood Sprgs. Rd. Bldg.600, Austin, TX 78759 United States
AB: New high-resolution seismic reflection profiles across the Central American volcanic arc (CAVA) reveal an asymmetric deformation pattern with large-scale folding and uplift of basinal strata in the forearc contrasted by intrusive bodies, normal faults, and possible strikes-slip faults in the backarc. Since Miocene times the CAVA has migrated seaward, apparently impinging on the Sandino forearc basin and creating or modifying the low-lying Nicaragua depression, which contains the backarc and much of the arc. However the structural nature of the depression and its possible relationship to forearc sliver movement is poorly known. In November-December 2004 we recorded a large, high-resolution, seismic reflection dataset largely on the Pacific shelf (forearc) area of Central America, extending from NW Costa Rica to the SE edge of El Salvador's territorial waters. We seized an opportunity to study the nature of the CAVA by recording data into the Gulf of Fonseca, a large embayment at the intersection of Nicaragua, Honduras, and El Salvador. With 3 GI airguns and a 2100 m streamer we recorded data with typical penetration of 2-3 seconds in the Sandino basin and frequency content of ~10-250 Hz (at shallow levels). Penetration was limited over the arc summit with high velocity volcanic rocks encountered at depths as shallow as a few hundred meters. To the NE the edge of the Nicaragua depression occurs abruptly; our data show a well-developed sedimentary basin 1.5-3 km thick separated by numerous steeply-dipping faults. The broadband signal and good penetration of this dataset will help us determine the chronology of arc development in this position and the styles of deformation in the forearc, arc, and backarc areas. In turn, this will help us understand the regional tectonic and stratigraphic development of this margin due to the profound affects of the arc.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 8104 Continental margins: convergent
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: Fall Meeting 2005