HR: 0800h
AN: T41B-1176    [Abstracts]
TI: Electrical Resistivity of Dehydrating Serpentinite
AU: * Bruhn, D
EM: dbruhn@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Raab, S
EM: raab@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Schilling, F
EM: fsch@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: The presence of fluids and melts in crustal rocks above subduction zones has often been attributed to the dehydration of subducting oceanic crust and hydrated mantle rocks. Dehydration processes have also been suggested to cause intermediate-depth earthquakes in the subduction zone. The most common mineral containing structurally bound water in the mantle is serpentine. By incorporating water into their crystal structure, serpentine minerals can store up to 13 wt% of water. This water is released when serpentines break down at elevated temperatures and pressures. In this study, we measured the electrical resistivity of dehydrating serpentinites and its evolution with time in laboratory experiments. Electrical properties of rocks respond highly sensitively to transiently available fluids, which are also detectable over very short time spans. The electrical resistivity measurements were performed at elevated pressure and temperature in a gas confining-medium pressure vessel at pressures of usually 600 MPa and temperatures up to 600\deg C, until a drop in resistivity was observed, indicating water was released from the rock. Our experimental setup was designed to be undrained, such that the water would be retained in the assembly. The resistance was determined with a high resolution impedance spectrometer with a spectrum of frequencies ranging from 100 mHz to 10 kHz. Several spectra were taken at each temperature step. In addition to the sample resistance, phase angles were recorded for each frequency. Generally, resistivity of the samples decreased by several orders of magnitude with increasing temperature, leveling off at about 300\deg C. The next drop in resistivity occurred at approx. 560\deg C, corresponding to the mineral phase change. Resistivities for all samples reached values of about 100 $\Omega$m, which is higher than expected for a fluid-saturated rock
DE: 5109 Magnetic and electrical properties
DE: 3914 Electrical properties
DE: 3924 High-pressure behavior
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting