HR: 1340h
AN: T23B-1412    [Abstracts]
TI: Cemented Mounds Perched on the Kane Megamullion Detachment Surface: A New Manifestation of Hydrothermal Venting?
AU: * Tucholke, B E
EM: btucholke@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Dick, H J
EM: hdick@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Tivey, M A
EM: mtivey@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AU: Humphris, S E
EM: shumphris@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States
AB: Hydrothermal venting has been widely investigated along the axes of mid-ocean ridges, but there has been little evidence of hydrothermal flow directly associated with major normal faults. A notable exception is the TAG hydrothermal field on the Mid-Atlantic Ridge (MAR), which is nucleated in the hanging wall above such a fault and which suggests that these fault/flow relations may be more common than heretofore recognized. We have encountered a probable example of such an association at Kane megamullion, which was formed by a long-lived (ca. 1.2 m.y.) detachment fault just south of Kane Fracture Zone on the MAR. The detachment fault exhumed sheeted dikes, gabbros, and mantle peridotites. Interpreted hydrothermal cementation and sediments occur on the detachment surface and take two forms: 1) consolidated mounds of mixed rock debris and cemented sediment that appears to be enriched in Mn- and Fe-rich hydrothermal precipitates, and 2) cemented, slabby sedimentary layers that also are Mn- and Fe-rich. The mounds have variable shapes and sizes. They range from conical to elongate or ridge-like and have heights from ca. 1 to 8 meters, with flank slopes of ca. 30 degrees to near-vertical. Compositions of the mound surfaces range from nearly pure rock debris (primarily basalt, but also occasional gabbro and serpentinite), to polymict breccia, to nearly pure sediment. Some of the sedimentary mounds show flow structures that resemble basalt pillows. The slabby sedimentary layers in some places occur on the flanks or at the bases of mounds and in other places occur on relatively smooth seafloor. The latter form is often cracked in linear to polygonal patterns, with upturned ridges produced at the cracks. We hypothesize that the debris mounds were produced where point-source fluid venting occurred through the hanging wall close to the active trace of the detachment fault. The fluids cemented the hanging-wall debris and affixed it to the emerging footwall while the surrounding unconsolidated debris wasted away down the sloping fault surface. The predominantly sedimentary mounds, as well as the cemented slabby sediments, may have formed in association with diffuse venting of low-temperature fluids through the footwall as it was exhumed and subjected to extensional bending stresses. If our hypothesis is correct, it indicates that primary pathways of fluid flow are intimately associated with major normal faults and probably also with fracture patterns in the emerging, bending footwalls of the faults.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 3075 Submarine tectonics and volcanism
DE: 8010 Fractures and faults
SC: Tectonophysics [T]
MN: 2007 Fall Meeting