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Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America
Stratigraphic and Structural Investigations
of Nicaraguan forearc and Intra-arc Tectonics
Kirk McIntosh (kirk@ig.utexas.edu), Craig Fulthorpe (craig@ig.utexas.edu), Jason Stephens (jstephens@mail.utexas.edu), Paul Mann (paulm@ig.utexas.edu), Justin Funk (jofunk@mail.utexas.edu)
Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin
We have recorded seismic and other geophysical data across the Nicaragua margin from the Cocos Plate to the Central American volcanic arc. These data demonstrate relatively long-term stability in the forearc region punctuated with periods of deformation, particularly along its landward and southeast boundaries. We are currently using stratigraphic relationships in the forearc basin to provide regional timing constraints for the observed deformation as well as trying to better define structural styles. Along much of the Pacific coast, both onshore and offshore, a belt of Miocene and younger convergent deformation has been recognized. Subsequently, the active volcanic arc has migrated, or jumped westward and becomes very near the Pacific coast in northwestern Nicaragua. Here not clear whether arc processes have influenced or obscured the compressional belt, but no anticlines are present in the offshore area, only a consistent seaward-dipping section of uplifted strata is present, and onshore the area is covered by Quaternary volcanics. Two seismic profiles into the Gulf of Fonseca, crossing the current volcanic arc, suggest that compressional deformation was absent or limited here. These profiles indicate that the arc has intruded the Sandino forearc basin stratigraphic section and they also delineate the Nicaragua depression. Here the magmatic edifice is marked by seismic velocities and potential field data, and an abrupt fault boundary occurs to the northeast where young, very-low-velocity sediments fill the depression. This zone may be part of a pull-apart zone related to northwestward forearc sliver motion as numerous high-angle faults occur with complicated cross-fault structural relationships.
Poster Session
