HR: 1330h
AN: S22A-0428    [PDF]
TI: Water Weakening of Clinopyroxene in the Diffusion Creep Regime
AU: Kohlstedt, D L
EM: dlkohl@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: * Majumder, S
EM: maju0003@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Mei, S
EM: mei@llnl.gov
AF: Lawrence Livermore National Laboratory, Lawrence Livermore National Laboratory, Livermore, Ca 94550 United States
AB: We investigated water weakening of clinopyroxene aggregates, prepared by hot pressing ground powder of natural Sleaford Bay clinopyroxenite consisting of Fe bearing diopside of composition Ca$_{0.97}$Mg$_{0.78}$Fe$_{0.26}$Si$_{1.99}$O$_{6}$. Wet and dry aggregates were deformed at a confining pressure of 300 MPa at temperatures between 1323-1423 K and 1398-1503 K, respectively. Water was added to the sample during the run by dehydration of a talc sleeve. The wet aggregates crept about 15 times faster than the dry aggregates. The stress exponent in both cases was $n = 1 $. The activation energies under the water-saturated and under-saturated conditions were 342 $\pm$ 27 and 759 $\pm$ 23 kJ/mol, respectively. We suggest that under water-saturated conditions, water derived point defects become the majority point defects and the charge neutrality condition changes into $\mathrm{\left[Fe_{Si}^{\prime} \right] = \left[ OH_O^{\cdot} \right]}$ from $\mathrm{\left[V_{Fe}^{\prime \prime}\right] = \left[ Fe_{i}^{\cdot \cdot} \right]}$. Comparison of water weakening of clinopyroxene, olivine and anorthite aggregates deforming in the diffusion creep regime suggests that of these three minerals, water weakening is most significant in clinopyroxene.
DE: 3900 MINERAL PHYSICS
DE: 3902 Creep and deformation
SC: Seismology [S]
MN: 2003 Fall Meeting