HR: 1330h
AN: V42A-0320    [PDF]
TI: Seismic Properties of Rocks at High PT Conditions. Laboratory Measurements on Mafic and Ultramafic Rocks Representative of Subduction Zones
AU: * Prelicz, R M
EM: ruth.prelicz@erdw.ethz.ch
AF: Geological Institute, ETH, Sonneggestr. 5, Zurich, 8092 Switzerland
AU: Burlini, L
EM: luigi.burlini@erdw.ethz.ch
AF: Geological Institute, ETH, Sonneggestr. 5, Zurich, 8092 Switzerland
AU: Kunze, K
EM: karsten.kunze@erdw.ethz.ch
AF: Geological Institute, ETH, Sonneggestr. 5, Zurich, 8092 Switzerland
AU: Burg, J
EM: jpb@erdw.ethz.ch
AF: Geological Institute, ETH, Sonneggestr. 5, Zurich, 8092 Switzerland
AB: The geological interpretation of geophysical data requires the knowledge of the physical properties of rocks and in particular of the effects of confining pressure and temperature. Of particular interest for the interpretation of the structures in subduction zones is the relationship between seismic anisotropy and rock fabric. Eclogites, peridotes and pyroxenites as well as some amphibolitic mylonites were collected in the western gneiss region in Norway and in the Bragansa massif in NE-Portugal. For each sample the modal composition and density was determined and on some selected samples the CPO was also measured. P wave velocities were measured on three orthogonal cylinders cut parallel (or normal) to the foliation and lineation (when visible) at elevated pressures and temperatures. The velocity measurements were correlated with predictions based on the determined modal composition, CPO and rock microstructure. The velocities were measured using the pulse transmission technique in an internally heated argon gas confining medium Paterson apparatus, up to 500 MPa confining pressure, and temperatures up to 700$\deg$C for specimens of 22mm diameter and up to 1200$\deg$C for specimens of 15 mm diameter (in all cases length is about 30mm). In order to keep the transducers away from the hot zone, buffer rods of PSZ or Al2O3 were introduced. Advantages of this setup are: Pressure is really hydrostatic and can be determined within 1 MPa: Temperature, is within 1K over the whole sample length at 700$\deg$C and 20K at 1200$\deg$C. Another advantage is that no cracking of the sample occurs after PT cycling. This means that no local stresses are raised, and therefore several runs can be performed with the same specimen. Here we will present the first measurements on a chlorite-peridotite, and the several improvements of the experimental set up and the measuring technique. The peridotite has a mean velocity of 7.9 Km/s at 500 MPa. Pressure derivative is of 2E-4 km/s/MPa and temperature derivative is -5E-5 km/s/K. The seismic anisotropy at 500 MPa was about 5.5%.
DE: 5102 Acoustic properties
DE: 8030 Microstructures
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting