HR: 16:30h
AN: T34B-03    [Abstracts]
TI: Detachment Shear Zone of the Atlantis Massif Oceanic Core Complex
AU: * Karson, J
EM: jkarson@duke.edu
AF: Divison of Earth & Ocean Sciences, Duke University, Durham, NC 27708 United States
AU: Fruh-Green, G
EM: frueh-green@erdw.ethz.ch
AF: Department of Earth Sciences, ETH-Zurich, Zurich, CH-8092 Switzerland
AU: Kelley, D
EM: kelley@ocean.washington.edu
AF: School of Oceanography, University of Washington, Seattle, WA 98195 United States
AU: Yoerger, D
EM: dyoerger@whoi.edu
AF: Applied Ocean Physics & Engineering, Woods Hole Oceanographic Insittution, Woods Hole, MA 202543 United States
AU: Jakuba, M
EM: jakuba@whoi.edu
AF: Applied Ocean Physics & Engineering, Woods Hole Oceanographic Insittution, Woods Hole, MA 202543 United States
AB: Near-bottom investigations of the cross section of the Atlantis Massif exposed in a major tectonic escarpment along the Atlantis Transform Fault provide an unprecedented view of the internal structure of the footwall domain of an oceanic core complex. Integrated direct observations, photogeology, and imaging define a mylonitic, low-angle detachment shear zone (DSZ) along the crest of the massif. The shear zone may project beneath the nearby, corrugated upper surface of the massif. The DSZ and related structures are inferred to be responsible for the unroofing of lower crustal gabbros and upper mantle peridotites by extreme, localized tectonic extension during seafloor spreading over the past 2 m.y. Strongly foliated serpentinites and talc-amphibole schists of the DSZ are about 100 m thick and can be traced continuously for at least 3 km in the spreading direction. Foliated DSZ rocks grade structurally downward into more massive basement rocks that lack a pervasive low-temperature deformation fabric. The main DSZ and underlying basement rocks are cut by discrete, anastomosing normal-slip, shear zones. Widely spaced, steeply dipping, normal faults cut all the older structures and localize serpentinization-driven hydrothermal outflow at the Lost City Hydrothermal Field. A thin (few meters) sequence of sedimentary breccias grading upward into pelagic limestones directly overlies the DSZ and may record a history of progressive rotation of the shear zone from an earlier moderately dipping attitude into its present, gently dipping orientation during lateral spreading and uplift.
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
DE: 8010 Fractures and faults
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8012 High strain deformation zones
DE: 8025 Mesoscopic fabrics
SC: Tectonophysics [T]
MN: Fall Meeting 2005