HR: 1340h
AN: T23B-1411    [Abstracts]
TI: Models of Deformation of Uppermost Oceanic Lithosphere: Comparison of Crustal Flexure in the Blönduós Area, Northern Iceland, and Structure of East Pacific Rise Crust at Hess Deep
AU: * Horst, A J
EM: ajhorst@syr.edu
AF: Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070, United States
AU: Karson, J A
EM: jakarson@syr.edu
AF: Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070, United States
AU: Varga, R J
EM: rvarga@wooster.edu
AF: Department of Geology, College of Wooster, 1189 Beall Ave., Wooster, OH 44691, United States
AU: Gee, J S
EM: jsgee@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0220, United States
AB: Models of the internal structure of oceanic crust have been constructed from studies of ophiolites and from more recent observations of tectonic windows into the upper crust. Spreading rate and/or magma supply are the central variables that control ridge processes and the ultimate architecture of ocean crust. In addition to ophiolites, Iceland also provides an important analog to study mid-ocean ridge processes and structure. Flexure zones in Iceland characterize the structure of Tertiary-Recent lava flows, and are areas wherein lavas dip regionally inward toward the axis of one of several ~N/S-trending rift zones. These rift zones are interpreted to represent fossil spreading centers which were abandoned during a series of eastward-directed ridge jumps. In the Hildará area, north-central Iceland, the eastern side of a regional flexure is characterized by westward-dipping lavas, approximately 6-8 Ma, which are cut by east-dipping normal faults and dikes. The upper-crustal structure within this flexure zone from slow spread (~20 mm/yr) crust exhibits remarkable similarities to the structure of the upper crust created at a fast-spreading (110 mm/yr) segment of the East Pacific Rise (EPR) observed at Hess Deep. In this modern ocean setting, ~1 Ma crust is characterized by west-dipping lavas above consistently east-dipping (away from the EPR) dikes and dike-subparallel fault zones. In both locations, paleomagnetic and structural data indicate that west-dipping lavas and east-dipping dikes result from tectonic rotations. In addition, cross-cutting dike relationships demonstrate that dike intrusion occurred both during and after normal fault- related tilting. These data indicate that fault-controlled tilting was initiated within the narrow neovolcanic zone of the ridge and is not associated with off-axis processes. Lavas at magmatically robust ridges commonly flow away from elevated ridge-crests. Measurement of anisotropy of magnetic susceptibility (AMS) of the lavas from the flexure in Iceland suggests a mean flow direction to the northeast, that is, away from the fossil-ridge axis, demonstrating that the fossil spreading center from which the lavas were extruded was located to the west. Despite the distinct differences in spreading rates, the high magma supply in both environments resulted in a very similar upper crustal architecture.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
DE: 8010 Fractures and faults
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2007 Fall Meeting