HR: 1340h
AN: OS33A-1467    [Abstracts]
TI: Tectonism and Long-Lived Hydrothermal Systems: Seismic Constraints From the TAG Segment, Mid-Atlantic Ridge 26°N
AU: * Canales, J
EM: jpcanales@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AU: Reves-Sohn, R
EM: rsohn@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AU: Humphris, S
EM: shumphris@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 United States
AB: Tectonic control is thought to play a prominent role in the evolution of long-lived hydrothermal systems at slow-spreading mid-ocean ridges. In 2003, we conducted an active-source seismic experiment in the TAG segment and hydrothermal mound (Mid-Atlantic Ridge, 26°N) to understand the relationship between long-lived hydrothermal activity, faulting, and the presence of crustal magma reservoirs. Two-dimensional travel-time tomography reveals that the TAG hydrothermal mound sits on a thin section of tectonized basalt overlying a crustal section of unusually high seismic velocities. This crustal anomaly extends for ~15 km along the axis of the segment, and ~5 km across the eastern valley wall, and it is characterized by seismic velocities typical of lower crustal rocks at depths as shallow as ~1 km below the seafloor. No low seismic velocities indicative of hot rock or magma reservoirs are found immediately beneath the hydrothermal mound. In contrast, ``normal'' seismic velocities are found along the western side of the valley floor beneath the neovolcanic zone, a few km west of the TAG mound. These observations indicate that the TAG hydrothermal mound is positioned above a long-lived fault that has uplifted and exposed lower crustal rocks that has along the eastern valley wall by tectonic extension. Our results appear to require that the heat source for the TAG system is located more than 7 km from the active mound, demonstrating that long-lived faults can focus hydrothermal fluid flow over long distances and large periods of time.
DE: 3035 Midocean ridge processes
DE: 7220 Oceanic crust
DE: 7245 Mid-ocean ridges
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005