Abstract
Electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (CpxXPl100−X, X = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 vol% (the signals of Cpx and Pl denote clinopyroxene and plagioclase, respectively) were measured in the YJ-3000t multi-anvil pressure and Solartron-1260 impedance spectroscopy analyzer at temperatures of 773–1073 K and pressures of 1.0–3.0 GPa. At the given pressure conditions, the electrical conductivity and temperature conformed to an Arrhenius relation. For the fixed mineralogical composition of Cpx50Pl50, the electrical conductivities of the samples significantly increased with the rise of temperature, but slightly decreased with increasing pressure. Furthermore, the activation energy and activation volume were determined as 1.06 ± 0.12 eV and 6.00 ± 2.00 cm3/mole, respectively. As for the various mineralogical compositions of dry gabbro, the electrical conductivities of the samples increased with the rise of volume percentage of clinopyroxene (Cpx) at 1.0 GPa. It is proposed that the main conduction mechanism is the small polaron, owing to the positive relation between the electrical conductivity and the iron content in samples. On the basis of these obtained conductivity results, laboratory-based electrical conductivity–depth profiles for the hot-pressed sintering gabbro with various mineralogical proportions and temperature gradients were successfully established. In conclusion, although the present acquired electrical conductivity results on the dry hot-pressed sintering gabbro with various mineralogical proportions cannot explain the high conductivity anomaly in the oceanic crust and West African craton, it can provide one reasonable constraint on the mineralogical composition in these representative gabbro-rich regions.
Highlights
As a representative basic intrusive rock, it is well known that gabbro is widely outcropped in these global tectonic units of oceanic crust and craton regions, and its corresponding dominant mineralogical composition is constituted of clinopyroxene and plagioclase [5,6]
In comprehensive considerations of all previously acquired conductivity results, we find that there exists one obvious discrepancy of almost three magnitude orders in the electrical conductivity of natural gabbro, which possibly originates from the differentiation of mineralogical proportion, water content, and accessory minerals
We measured the electrical conductivities of dry gabbro with various mineralogical proportions
Summary
The natural gem-grade clinopyroxene (Cpx) and plagioclase (Pl) single crystals were chosen as the starting materials in order to synthesize the gabbro. The hot-pressed sintering gabbro was kept in the vacuum dry furnace at 423 K for at least 12 h before the in situ electrical conductivity measurements. As pointed out by Yang and Heidelbach [19], when the grain size of hot-pressed sintering synthetic clinopyroxene is larger than 10 μm, the influence of grain size on the electrical conductivity of a sample can be negligible under conditions of similar temperature and pressure ranges. To accurately determine the water contents in the hot-pressed sintering gabbro before and after electrical conductivity experiments, the infrared spectra of samples were measured for each individual constituent Cpx and Pl mineral phases by a Fourier transform infrared spectrometer (Vertex-70V and Hyperion-1000 infrared microscope). The FT-IR absorption spectra for clinopyroxene and plagioclase were conducted within the wavenumber range of 3000–4000 cm−1 in the hot-pressed sintering gabbro, respectively. A detailed description for the FT-IR measurement was given in the previous reference [21]
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