HR: 1340h
AN: V53A-1532    [Abstracts]
TI: Incorporation of seawater into mid-ocean ridge lava flows during emplacement
AU: * Soule, S A
EM: ssoule@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Fornari, D J
EM: dfornari@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Perfit, M
EM: perfit@geology.ufl.edu
AF: University of Florida, Dept. of Geological Sciences, Gainesville, FL 32611 United States
AU: Cann, J R
EM: joe@earth.leeds.ac.uk
AF: University of Leeds, School of Earth Sciences, Leeds, LS2 9JT United Kingdom
AU: Montési, L
EM: lmontesi@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Ridley, W I
EM: iridley@usgs.gov
AF: US Geological Survey, Denver Federal Center, Denver, CO 80225 United States
AB: Mid-ocean ridge (MOR) lava flows erupted at ~2000-3500 m below sea level contain large, cm- to m-sized cavities close to the upper surfaces of the flows. Within these cavities, lava drips (similar to lava stalactites found in terrestrial lava tubes) hang from the base of the upper crust. In order for these features to form, the cavities must exist as vapor-filled open space under hydrostatic pressures up to 35 MPa, and must maintain near-magmatic temperatures to attain the observed morphology of the drips. We have examined numerous lobate and sheet lava crusts from the fast-spreading East Pacific Rise in order to constrain the nature of the vapor that filled the cavities beneath these crusts, the extent of the interaction between the vapor and the liquid lava, and the impact of the vapor phase on flow emplacement. On the inner surfaces of large vesicles and cavities within the flow are mineral phases that appear to have grown at the interface between the liquid lava and vapor. These mineral phases have compositions distinct from those found in the flow interior (e.g., pure albite and forsterite), and show mineral growth habits indicative of undercooling of the lava. Preliminary thermodynamic modeling of the gas-liquid-solid interaction suggests that vapor derived from heated seawater is capable of producing the observed mineral compositions. In addition, we have found that quenched glass adjacent to analyzed vesicles can be enriched in Cl by an order of magnitude over ambient glass within the same sample suggesting that local mass exchange between the seawater and the lava has occurred. Here we present results of these analyses and accompanying thermodynamic modeling that lead us to conclude that the vapor filling the cavities is derived directly from seawater. In addition, we present numerical models investigating mechanisms for seawater incorporation and its impact on flow emplacement.
DE: 8412 Reactions and phase equilibria (1012, 3612)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8429 Lava rheology and morphology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005