The in situ electrical conductivity of hydrous garnet samples (Py(20)Alm(76)Grs(4)-Py(73)Alm(14)Grs(13)) was determined at pressures of 1.0-4.0 GPa and temperatures of 873-1273 K in the YJ-3000t apparatus using a Solartron-1260 impedance/gain-phase analyzer for various chemical compositions and oxygen fugacities. The oxygen fugacity was controlled by five solid-state oxygen buffers (Fe2O3 + Fe3O4, Ni + NiO, Fe + Fe3O4, Fe + FeO, and Mo + MoO2). Experimental results indicate that within a frequency range from 10(-2) to 10(6) Hz, electrical conductivity is strongly dependent on signal frequency. Electrical conductivity shows an Arrhenius increase with temperature. At 2.0 GPa, the electrical conductivity of anhydrous garnet single crystals with various chemical compositions (Py(20)Alm(76)Grs(4), Py(30)Alm(67)Grs(3), Py(56)Alm(43)Grs(1), and Py(73)Alm(14)Grs(13)) decreases with increasing pyrope component (Py). With increasing oxygen fugacity, the electrical conductivity of dry Py(73)Alm(14)Grs(13) garnet single crystal shows an increase, whereas that of a hydrous sample with 465 ppm water shows a decrease, both following a power law (exponents of 0.061 and -0.071, respectively). With increasing pressure, the electrical conductivity of this hydrous garnet increases, along with the pre-exponential factors, and the activation energy and activation volume of hydrous samples are 0.7731 +/- 0.0041 eV and -1.4 +/- 0.15 cm(3)/mol, respectively. The results show that small hopping polarons (Fe-Mg(center dot)) and protons (H-center dot) are the dominant conduction mechanisms for dry and wet garnet single crystals, respectively. Based on these results and the effective medium theory, we established the electrical conductivity of an eclogite model with different mineral contents at high temperatures and high pressures, thereby providing constraints on the inversion of field magnetotelluric sounding results in future studies.

Publication name	CONTRIBUTIONS TO MINERALOGY AND PETROLOGY　Volume: 163 　Issue: 4 　Pages: 689-700　Published: APR 2012
Author(s)	Dai, Lidong; Li, Heping; Hu, Haiying; Shan, Shuangming; Jiang, Jianjun; Hui, Keshi
Corresponding author	LI Heping  hepingli_2007@hotmail.com  Chinese Acad Sci, Inst Geochem, Lab Study Earths Interior & Geofluids, Guiyang 550002, Guizhou, Peoples R China

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