- 责任者：Men Qingbo (State Key Laboratory for Mineral Deposits Research ; School of Earth Sciences and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Wang Qin
- 刊名：Acta Petrologica et Mineralogica
- 出版年：2013
- 卷期：32(5)
- 关键词：石榴子石辉石岩 ; garnet pyroxenite ; 电导率 ; electrical conductivity ; 底侵作用 ; underplating
- 页码：p.652-662
- 图表：5 illus., 2 tables, 56 refs.
- 分类号：0801
- issnNo：ISSN1000-6524
- isbnNo：CN11-1966/P
Garnet pyroxenite xenoliths from the Hannuoba Cenozoic basalt were formed by magmatic underplat- ing in the uppermost mantle （40--45 kin）, and represent the crust-mantle transition zone. The electrical con- ductivity of sintered garnet pyroxenite WD958 was measured at 1.2 GPa and 380 -- 900℃, using a Solartron 1260 Phase-Gain Analyzer. The temperature dependence of electrical conductivity （a） can be fitted by an Arrhe- nius equation： a - o0 exp（ - AH/kT）, where T is in Kelvin and k is the Dohzmann constant. Values of the pre- exponential factor （a0） and activation enthalpy of electric conductivity （AH） of sample WD958 are 97.5 S/m and 1.27 eV, respectively. The water contents of minerals were analyzed using the Fourier transform infrared spectrometry. The average water content in clinopyroxene is 117 ×10-6 H2O, whereas olivine is very dry （〈 1 ×10-6H20） and the water content in garnet cannot be determined due to alteration. The laboratory-derived electrical conductivity of mantle minerals shows that the calculated conductivity using the Hashin-Shtrikman av- erage can match the measured values by assuming a mixture of hydrogen-bearing clinopyroxene, dry garnet and dry olivine. This demonstrates the contribution of both small polaron conduction and proton conduction mecha- nisms to the bulk conductivity of garnet pyroxenite, and the sample can be regarded as a resistive matrix with non-interconnected conductive inclusions. If the water partition equilibrium between minerals is preserved at the in situ depth （40--45 km）, the electrical conductivity of garnet pyroxenite will be enhanced by 1 order magni- tude and the proton conduction mechanism becomes predominant. For the lithosphere with a high geothermal gradient, the temperature at the Moho depth could reach 1 000 ℃ and garnet pyroxenite is characterized by high conductivity. In contrast, under normal geothermal gradients, garnet pyroxenite shows conductivity as low as spinel lherzolite. During magmatic underplating, therefore, the electrical crust-mantle boundary will vary with temperature and water concentration.