HR: 14:10h
AN: T33G-03    [Abstracts]
TI: Microearthquake Survey of the TAG Segment, Mid-Atlantic Ridge (26°N): The Early Stages of Deformation on a Detachment Fault Revealed
AU: * deMartin, B
EM: bjd@mit.edu
AF: Dept. of Geology and Geophysics, WHOI, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Reves-Sohn, R
EM: rsohn@whoi.edu
AF: Dept. of Geology and Geophysics, WHOI, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Canales, J P
EM: jpcanales@whoi.edu
AF: Dept. of Geology and Geophysics, WHOI, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Humphris, S
EM: shumphris@whoi.edu
AF: Dept. of Geology and Geophysics, WHOI, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AB: Long-term deformation along a detachment fault has been recognized as a mechanism for exhumation of oceanic core complexes, which have been found at the inside-corner high of ridge offsets along slowly diverging plate boundaries. The mechanisms by which detachments are initiated and the geometry and depth of faulting, however, are not well understood. Recent work has demonstrated that the TAG hydrothermal mound on the Mid-Atlantic Ridge at 26°N is situated above a detachment fault and hypocenters from a nine month microearthquake survey (June 2003 - March 2004) provide new insight into the early stages of core complex formation. The instrument network consisted of thirteen, four-component ocean bottom seismometers deployed in a 3-ring pattern around the active TAG hydrothermal mound with a total aperture of 7 x 7 km. Approximately 35,000 events were detected during the deployment, and to this point we have located 1,323 events from 13 days of data. Hypocenter analysis reveals two distinct zones of seismicity. One set of events strikes parallel to the ridge and is apparently associated with normal faulting on the east side of the axial valley. The second set of events forms an arc that closely mimics the morphology of the nascent inside-corner high, intersecting with the ridge parallel events at points that may demarcate the along-axis limits of the detachment. The overall pattern of seismicity resembles a bow in map view, with an aseismic region encompassing the zone of active and relict hydrothermal circulation and the magnetic low. We hypothesize that the arcuate pattern of seismicity results from doming and uplift of serpentinized mantle on the detachment footwall.
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005