HR: 1340h
AN: T33D-0583    [Abstracts]
TI: Faulting and Focused Fluid Flow in Superfast, EPR Crust Near Pito Deep.
AU: * Hayman, N W
EM: hayman@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, NC 27708 United States
AU: Gillis, K
EM: kgillis@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8W 3P6 Canada
AU: Karson, J A
EM: jkarson@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, NC 27708 United States
AB: Exposures of ~3 Ma superfast (~144mm/yr) spread EPR crust in ~4 km-high escarpments near Pito Deep allow investigation of the relationship between deformation and alteration. Much of the crust exposed at Pito Deep is remarkably undeformed. However, faults distributed throughout the dike complex accommodate local, minor changes in dike orientation. The faults apparently offset the dike-lava transition by >>10 m but changes in thickness of the lavas and dike emplacement into the lava section contribute to this amount. Locally dikes intrude the fault zones and the faults contain mineral assemblages associated with axial hydrothermal systems. Thus most of the faults are interpreted as axial rather than being related to the opening of Pito Deep. Individual faults within wider zones are ~1 m-wide and samples of fault rocks include gouges and cataclasites with abundant veins. Fault rocks are pervasively altered and deformed and commonly lack igneous textures. Fracture and veining appear to dominate over frictional wear as deformation mechanisms that generated the fault rock. Multiple generations of veins include both mm-scale veins sealed by crystals, and vuggy veins that are up to several centimeters wide and extend continuously for >10 m. Veins and fault-rocks are rich in chlorite, quartz, epidote, and euhedral sulfides. This alteration is distinct from the alteration away from fault zones, in terms of the dominant hydrothermal minerals and degree of alteration. It is hypothesized that the greenschist-grade fault- and vein-related alteration is due to the focused discharge of hydrothermal fluids. The fluid flow was regulated by porosity changes during and between increments of fault slip. Noteworthy is that the feedback between fluid flow and faulting did not affect larger areas. Rather, highly localized fault zones developed at specific times and places and evolved during spreading, leaving areas surrounding the fault zones relatively undeformed. This is in contrast with the intermediate-spread crust exposed along the north wall of Hess Deep, where deformation and alteration are more distributed and highly localized fault zones are rare.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 8100 TECTONOPHYSICS
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005