HR: 10:20h
AN: T22E-01 INVITED    [Abstracts]
TI: Black Smoker Vents and Oceanic Detachment Faults
AU: * McCaig, A M
EM: a.mccaig@see.leeds.ac.uk
AF: Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Cliff, R A
EM: b.cliff@see.leeds.ac.uk
AF: Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
AU: Escartin, J
EM: escartin.javier@gmail.com
AF: CNRS - Groupe de Géosciences Marines (CNRS UMR7097), Institute de Physique du Globe de Paris, Paris, 75252, France
AU: Fallick, A E
EM: t.fallick@suerc.gla.ac.uk
AF: Scottish Universities Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, United Kingdom
AU: MacLeod, C J
EM: macleod@cf.ac.uk
AF: School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, United Kingdom
AB: It is generally assumed that the seawater-derived fluids that feed black smoker vent fields on the seafloor are discharged vertically from depths of around 1 to 3 km. Yet several Atlantic vent fields are located several km away from the neovolcanic zone, and the TAG field is underlain by a zone of seismicity dipping toward the ridge crest. Fossil detachment faults at both 15^o 45' N and 30^o N are underlain by gabbro bodies surrounded by serpentinized peridotite and are intruded by syntectonic basaltic sills. Both faults show evidence for high fluid flux at black smoker temperatures in the form of metasomatic talc-tremolite-chlorite assemblages replacing ultramafic rocks, and intense alteration of oxygen and strontium isotopes. Fluids in equilibrium with this assemblage would be similar to ultramafic-hosted black smoker fluids. We present a new model in which hydrothermal circulation around detachment faults evolves from hangingwall basalt-hosted (TAG-type) to footwall ultramafic-hosted (Rainbow-type) to low temperature ultramafic-hosted (Lost City type) as displacement on the detachment increases. Key features of our model are the intrusion of gabbro bodies immediately below the detachment to provide a heat source for circulation, and focusing of fluid flow into the detachment fault to allow venting away from the neovolcanic axis.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting