HR: 15:10h
AN: V33C-07    [Abstracts]
TI: Constraints on Grain-Scale Transport of Fluid in the Sub-Arc Mantle
AU: * Price, J D
EM: pricej@rpi.edu
AF: Rensselaer Polytechnic Institute, Dept. of Earth & Environmental Sciences 110 8th St., JSC 1W19, Troy, NY 12180 United States
AU: Wark, D A
EM: warkd@rpi.edu
AF: Rensselaer Polytechnic Institute, Dept. of Earth & Environmental Sciences 110 8th St., JSC 1W19, Troy, NY 12180 United States
AU: Watson, E B
EM: watsoe@rpi.edu
AF: Rensselaer Polytechnic Institute, Dept. of Earth & Environmental Sciences 110 8th St., JSC 1W19, Troy, NY 12180 United States
AU: Thomas, J B
EM: thomaj2@rpi.edu
AF: Rensselaer Polytechnic Institute, Dept. of Earth & Environmental Sciences 110 8th St., JSC 1W19, Troy, NY 12180 United States
AB: It is generally accepted that fluid-induced melting feeds arc magmatism above subduction zones. Presumably, these fluids ascend from the region where they are generated, near the top of the subducting slab, up the thermal gradient to super-solidus regions. Modeling indicates that given the amount of H₂O found in arc igneous materials, transport is not accomplished by either volumetric or intergranular diffusion. However, porous flow through interconnected grain-scale pores provides a plausible way to transport this fluid through the lower portion of the mantle wedge. We have conducted several series of experiments on rock + fluid systems to better constrain the nature of grain-scale fluid energetics (γ), porosity (Φ) and permeability (k), relevant to fluid transport in the mantle. Our results have shown that k = d² Φ ³ / 270 for pore networks similar to those observed in experiments on dunite at high pressure, with low dihedral angles (< 60°) and dominated by curved pore walls. We have shown that permeability may be enhanced through fluid partitioning in regions with variable grain size (e.g. shear zones), and that k is significantly reduced in pore networks with high dihedral angles (≥ 60°) and those dominated by facets (perhaps in amphibole-rich hydrated mantle). We have shown, in addition, that k is largely unaffected by volumetrically minor pore-hosted grains, and that thermal-gradient induced permeability-enhancing channels are not likely to form in the mantle wedge. Assuming steady-state production of fluid, a flux likely released through arc magmatism, and a grain size of 10 mm, modeling suggests that mantle peridotite has a minimum grain-scale Φ of 3 to 7 × 10^-5. This may permit fluid transport from the source region to the site of melting.
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3621 Mantle processes (1038)
DE: 3640 Igneous petrology
DE: 3653 Fluid flow
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005