HR: 14:25h
AN: T23F-04    [Abstracts]
TI: Internal structure of axial hydrothermal systems revealed at tectonic windows
AU: * Gillis, K M
EM: kgillis@uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6 Canada
AB: Tectonic exposures of the oceanic crust provide views of the internal structure of mid-ocean ridge hydrothermal systems. Targeted exploration of escarpments that formed at the fast- to very fast-spreading East Pacific Rise exposed at Pito and Hess Deeps have allowed us to address questions that 1-D 'pinpricks' afforded by ocean drilling cannot. Outcrop imaging along closely spaced submersible and ROV tracks document the geological context of hydrothermal alteration in 3-dimensions. These broad views reveal how and why the conditions and products of fluid-rock reaction were spatially and temporally variable, how deformation patterns influenced fluid flow pathways, and the linkages between the magmatic and hydrothermal activity. Tectonic exposures record the time-integrated history of fluid-rock interaction and fluid fluxes that result primarily from steady-state hydrothermal systems. Regional scale (100s metres) variability in hydrothermal alteration patterns reflects both the spatial position within hydrothermal systems and temporal variability of tectonic-magmatic cycles. In the former case, conditions of fluid-rock interaction will vary along both recharge and discharge pathways with the so-called reaction zone being manifest in different ways, depending upon the style of deformation. In the latter case, whether a mid-ocean ridge is in a magmatic or tectonic phase will profoundly influence crustal alteration. More extensive faulting during a tectonic phase would, for example, provide more fluid flow pathways, to deeper levels, thus deepening the magma-hydrothermal transition. During a magmatic phase, perturbations such as dike injection and cracking events impact hydrothermal systems by providing transient connections to the overlying hydrothermal system. At the same time, exogenic components can be cycled into axial magma chambers by the assimilation of hydrothermally altered crust and pore fluids. These and other predictions about crustal accretion processes have been made from seismic and vent fluid data, as well as theoretical approaches. The record of fluid-rock interaction afforded by tectonic windows provides critical tests of these predictions.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
SC: Tectonophysics [T]
MN: Fall Meeting 2005