Lidong Dai,Haiying Hu,Wenqing Sun,Heping Li,Changcai Liu,Mengqi Wang
The electrical conductivity of dry sintered olivine aggregates with various contents of magnetite (0, 3, 5, 7, 10, 20, and 100 vol. %) was measured at temperatures of 873–1273 K and a pressure of 2.0 GPa within a frequency range of 0.1–106Hz. The changes of the electrical conductivity of the samples with temperature followed an Arrhenius relation. The electrical conductivity of the sintered olivine aggregates increased as the magnetite-bearing content increased, and the activation enthalpy decreased, accordingly. When the content of interconnected magnetite was higher than the percolation threshold (~5 vol. %), the electrical conductivity of the samples was markedly enhanced. As the pressure increased from 1.0 to 3.0 GPa, the electrical conductivity of the magnetite-free olivine aggregates decreased, whereas the electrical conductivity of the 5 vol. % magnetite-bearing sample increased. Furthermore, the activation energy and activation volume of the 5 vol. % magnetite-bearing sintered olivine aggregates at atmospheric pressure were calculated to be 0.16 ± 0.04 eV and −1.50 ± 0.04 cm3/mole respectively. Due to the high value of percolation threshold (~5 vol. %) in the magnetite impurity sample, our present results suggest that regional high conductivity anomalies in the deep Earth’s interior cannot be explained by the presence of the interconnected magnetite-bearing olivine aggregates.Keywords:electrical conductivity;magnetite;olivine aggregates;percolation threshold;high temperature and high pressure
Shenyang Y. Zhang,Hongluo L. Zhang,Zhenhui Hou,Dmitri A. Ionov,Fang Huang
A rapid sample preparation procedure is described to determine trace element compositions of peridotites using LA-ICP-MS. Peridotite powders were fused with albite in a molybdenum–graphite assembly to obtain homogeneous glasses. Best conditions for the fusion procedure (heating at 1500–1550 °C for 10–15 min with a sample-to-flux ratio of 1:2) were constrained with melting experiments on two USGS reference materials, PCC-1 and DTS-2B. Mass fractions of first series transition elements, Ba and Pb, in quenched glasses of PCC-1 and DTS-2B are consistent with published data within 10% RSD. Three spinel peridotite xenoliths from eastern China were analysed following both our method and conventional solution ICP-MS. Compared with solution ICP-MS, the relative deviations of our method for most elements were within 10%, while for the REE, Ta, Pb, Th and U, the relative deviations were within 20%. In particular, volatile elements (e.g., Pb and Zn) are retained in the glass. Compared with conventional wet chemistry digestion, our method is faster. Additional advantages are complete sample fusion, especially useful for samples with acid-resistant minerals (spinel and rutile), and long-term conservation of glasses allowing unlimited repeated measurements with microbeam techniques. The same approach can be used for analyses of other mantle rocks, such as eclogites and pyroxenites.
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