ELECTRICAL PROPERTIES OF GNEISSES IN THE UKRAINIAN SHIELD UNDER HIGH THERMOBARIC CONDITIONS
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dc.contributor.author | Lebedev T.S. | |
dc.contributor.author | Shepel S.I. | |
dc.date.accessioned | 2021-03-02T07:41:50Z | |
dc.date.available | 2021-03-02T07:41:50Z | |
dc.date.issued | 2001 | |
dc.identifier | https://elibrary.ru/item.asp?id=27759420 | |
dc.identifier.citation | Geophysical Journal, 2001, 20, 2, 299-318 | |
dc.identifier.issn | 0275-9128 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/26001 | |
dc.description.abstract | Thermobaric variation of electrical characteristics of sets of different gneisses from the Central Ukrainian Precambrian Shield were studied. Experiments were carried out on dry, air-dried and fluid-saturated samples at different temperatures (T) (high temperatures included) and pressures (P). Analysis of mean values of the electrical parameters studied showed that pyroxene-biotite gneisses had the lowest electrical resistivity. On the other hand, their dielectic coefficient ε was highest. This regularity can be explained by pyroxene-biotite gneisses being greatly affected by secondary transformations. The result was serpentinization of plagioclase and development of chlorites and amphiboles among dark-coloured minerals. The above processes caused additional defect domains to appear in the crystalline lattices of minerals. The latter reduced the activation energy (E) of current-carriers and resistivity (ρ). It was established that ρ of gneisses decreases from the dry to the water-saturated state. That transition is especially significant in high-resistivity gneisses. As mineralisation increases from 0.1 to 100 g/1, ρ decreases by an average of ≈1.5 orders of magnitude. Given the same concentration range of the salts with which the solutions are saturated, the ε increase rate is greatest in the low-frequency range. A relatively clear-cut relationship between porosity and electrical properties was established for gneisses. It was shown that ρ of water-saturated gneisses decreases when porosity increases, while their ε increases simultaneously. Moreover, the difference between the absolute ε and ρ values of potentially gold-productive and unproductive strata of this region, established under atmospheric PT conditions, persists at high temperatures. Studies of the variation of electrical resistivity in dry, air-dried and water-saturated gneisses under high temperature and quasi-hydrostatic pressure, simultaneously applied, showed that it depended considerably on water content. The increase of quasi-hydrostatic pressure reduces E and the transition temperature from extrinsic to intrinsic conductivity significantly. On the basis of system analysis of experimental data obtained, as well as on the data of P and T distribution in the Earth's crust of the Central Ukrainian Shield and the probable depth of occurence of gneisses, electrical resistivity values were predicted down to 15 km depth. | |
dc.subject | Precambrian | en |
dc.title | ELECTRICAL PROPERTIES OF GNEISSES IN THE UKRAINIAN SHIELD UNDER HIGH THERMOBARIC CONDITIONS | |
dc.type | Статья | |
dc.subject.age | Precambrian | en |
dc.subject.age | Докембрий | ru |
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