The electrical conductivity of eclogites measured by two methods

Laštovičková, Marcela; Buben, J.

doi:10.1007/bf01615815

Cited by 10 publications

(6 citation statements)

References 3 publications

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“…Our conductivity results on eclogite are in the good agreement with those of Laštovičková (1975), although a small discrepancy in the lower-temperature region may reflect the different mineralogical constituents of the two studies. The natural eclogite sample used by Laštovičková (1975) consisted of garnet (40%), clinopyroxene (45%), quartz (10%), amphibole (2%), rutile (2%), and minor symplectite minerals that include amphibole-plagioclase, diopside-plagioclase, and diopside-magnetite (1%). In the present study, in contrast, the samples consisted of varying volume ratios of garnet and clinopyroxene.…”

Section: Geophysical Implicationssupporting

confidence: 85%

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The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

Dai

et al. 2011

Contrib Mineral Petrol

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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 ). 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 Á Mg andprotons (H Á ) 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.

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Section: Geophysical Implicationssupporting

confidence: 85%

“…The clinopyroxene data are fromYang et al (2011a). The dashed line shows the electrical conductivity of eclogite during cooling at room pressure, as reported byLaštovičková (1975) Fig. 11Effect of garnet fraction on electrical conductivity of eclogite at conditions of 2.0 GPa, 873-1473 K and theNi-…”

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confidence: 97%

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

Dai

et al. 2011

Contrib Mineral Petrol

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“…[44] The temperature dependence of the electrical conductivity of eclogite samples is presented in Figure 7, and those of spinel lherzolite and mafic granulite samples are shown in Figure 8. The conductivity of At-Bashi eclogite measured in the laboratory compares well with the previous measurements by Laštovičková [1975], Laštovičková and Parkhomenko [1976], and Parkhomenko [1982]. The activation energy, ∼0.8 eV, and the absolute value of the electrical conductivity are slightly higher than in upper mantle eclogites.…”

Section: Electrical Conductivity Measurementssupporting

confidence: 84%

“…Electrical conductivity of At‐Bashi eclogite measured at 2.5 GPa in comparison with MT‐inversion conductivity. The average activation energy of At‐Bashi eclogite at 0.83 eV is in good agreement with the typical values of 0.66–1.00 eV [ Laštovičková , 1975]. Max and min are the upper and lower boundaries of eclogite conductivities for garnet‐rich (>40 vol%) and garnet‐poor (<20 vol%) eclogites [ Laštovičková and Parkhomenko , 1976], respectively.…”

Section: Electrical Conductivity Measurementsmentioning

confidence: 64%

State of lithosphere beneath Tien Shan from petrology and electrical conductivity of xenoliths

Bagdassarov¹,

Batalev²,

Egorova³

2011

J. Geophys. Res.

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[1] The shortening of Tien Shan and the evolution of its lithosphere have been evaluated from P-T geothermobarometry of xenoliths and from comparison of their electrical conductivity with conductivities obtained from the inversion of magnetotelluric (MT) data. Spinel lherzolite and granulite xenoliths found in basaltic outcrop Ortosuu represent upper mantle and crust beneath southern Tien Shan. The spinel lherzolite xenoliths correspond to the lithospheric mantle close to the crust-mantle boundary. The studied mantle xenoliths record two types of the upper mantle processes: a low-degree partial melting (about 7-10%) and a cryptic metasomatism. The granulite xenoliths are fragments of the lower crust captured from differing depths. The temperature and pressure estimates of the garnet granulite xenoliths indicate that they were derived from near the crust-mantle boundary. P-T equilibration conditions of mafic granulites and spinel lherzolites infer that the paleogeotherm corresponded to the heat flux 80-85 mW m −2 about 70-66 Myr ago. The present-day heat flux in the region is about 55-60 mW m −2 . The position of the Moho discontinuity 70-66 Myr ago was at a depth of 30-35 km, and the present depth of the Moho boundary is 55-60 km. The observed seismic P wave velocities above and below the present-day Moho boundary are 7.3 and 7.9 km s −1 , respectively. Elastic P velocities measured on xenoliths samples in laboratory and extrapolated to PT conditions of the Moho discontinuity (1.8 GPa and ∼750°C) are 6.8 km s −1 for the mafic granulite and 8.0 km s −1 for the spinel lherzolite. The electrical conductivity of xenoliths has been measured at 0.8-1.0 GPa and in the range between 500°C and 850°C for mafic granulites and at 1.0-1.5 GPa and from 500°C to 1050°C for spinel lherzolites. The contrast in conductivities between mafic granulite and spinel lherzolite samples under P-T conditions corresponding to the geotherm with the heat flux ∼60 mW m −2 agrees well with the contrast of MT electrical conductivity below and above the present-day Moho boundary at a depth of 55-60 km. Thus, the thickening of the Tien Shan lithosphere is about 25 ± 5 km. Before the shortening of Tien Shan about 20-30 Myr ago the lithosphere was rather hot, with a temperature of 500°C at a 15 km depth and of 850°C at the Moho boundary. In comparison to Tien Shan, the lithosphere beneath the neighboring Tarim Basin was rather cold, 350°C at the depth of 15 km and 500°C at the Moho boundary. These temperature differences were the main factors that caused the mechanical weakening of the Tien Shan crust and upper mantle. The modern strain rates of the Tien Shan shortening are 10 −14 × 3 to 10 −15 s . In the past the lithosphere strength beneath Tien Shan was ∼10 12 N m −1 , which was more than 1000 times weaker in comparison with the lithospheric strength of Tarim Basin at the beginning of the continental compression in the region.Citation: Bagdassarov, N., V. Batalev, and V. Egorova (2011), State of lithosphere beneath Tien Shan from petrology and e...

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“…Deformation during craton assembly might be one means of shearing the grains and establishing connectivity. However, there is almost no extant laboratory data on the bulk conductivity of eclogites, and what does exist does not show high conductivities [ Lastovickova and Buben , 1975].…”

Section: Discussionmentioning

confidence: 99%

Electrical lithosphere beneath the Kaapvaal craton, southern Africa

Evans¹,

Jones²,

García³

et al. 2011

J. Geophys. Res.

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[1] A regional-scale magnetotelluric (MT) experiment across the southern African Kaapvaal craton and surrounding terranes, called the Southern African Magnetotelluric Experiment (SAMTEX), has revealed complex structure in the lithospheric mantle. Large variations in maximum resistivity at depths to 200-250 km relate directly to age and tectonic provenance of surface structures. Within the central portions of the Kaapvaal craton are regions of resistive lithosphere about 230 km thick, in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography, but thinner than inferred from seismic body wave tomography. The MT data are unable to discriminate between a completely dry or slightly "damp" (a few hundred parts per million of water) structure within the transitional region at the base of the lithosphere. However, the structure of the uppermost ∼150 km of lithosphere is consistent with enhanced, but still low, conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for Kaapvaal xenoliths. The electrical lithosphere around the Kimberley and Premier diamond mines is thinner than the maximum craton thickness found between Kimberley and Johannesburg/Pretoria. The mantle beneath the Bushveld Complex is highly conducting at depths around 60 km. Possible explanations for these high conductivities include graphite or sulphide and/or iron metals associated with the Bushveld magmatic event. We suggest that one of these conductive phases (most likely melt-related sulphides) could electrically connect iron-rich garnets in a garnet-rich eclogitic composition associated with a relict subduction slab.

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The electrical conductivity of eclogites measured by two methods

Cited by 10 publications

References 3 publications

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

State of lithosphere beneath Tien Shan from petrology and electrical conductivity of xenoliths

Electrical lithosphere beneath the Kaapvaal craton, southern Africa

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