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Abstract

Information about results of studies of thermobaric changes of physical properties of rocks discovered in<br>drilling the Krivoy Rog ultradeep borehole (Ukraine) are summarized. Pethrophysical models of the Earth’s crust<br>of the area of its location are set up.<br>The main tasks of drilling this borehole located in an iron province which is one of the largest in the world were<br>to elucidate the formation conditions, composition, properties and evolution of the Earth’s crust of continental<br>type within the area of the development of precambrian iron-silicon and granite-greenstone formations of the<br>Central Ukrainian Shield. Also specified was the interpretation of anomalies of the observed geophysical fields<br>and the nature of seismic boundaries in crust.<br>For this purpose and to set up a regional petrophysical model of the interior we have obtained a new unique<br>information on PT-changes of physical characteristics of rocks discovered by the borehole. The drifted part of<br>the section is mainly represented by metaconglomerates, various schists, quartzites, amphibolites,<br>plagiogranites and some other lower-proterozoic and upper-archean mineral formations of different<br>composition. Almost all rocks encountered in drilling show differently expressed banding, schistosity and linear<br>arrangement of minerals.<br>The method worked out earlier in which specialized chambers are used was applied in a set of laboratory<br>petrophysical PT-experiments on samples of a representative collection of cores. We carefully studied elastic,<br>thermal, electrical and magnetic parameters of rocks in characteristic strictly oriented structural and textural<br>with simulating respective deep thermobaric conditions in PT-experiments. We are founding the nature of the<br>anisotropy of the distribution of the studied petrophysical parameters found within the section and which is<br>most probably preserved even at greater depth (below the hole bottom).<br>The features of thermobaric changes of specific electrical resistance and dielectrical constant of the rocks<br>studied are due to their saturation with fluids, mineralization of the latter, dissociation and dehydration of<br>carbonates, micas and other minerals. With increasing pressure the thermal conductivity and thermal diffusivity<br>coefficients of rocks are increased by almost one third. They evently decrease with increasing temperature. We<br>have established a relatively early stage of metamorphism of mineral formations. At the simultaneous<br>programmed PT-effect the remanent magnetization of the most samples containing ferromagnetics is featured<br>by anomalous changes in respective directions. Based on experimental PT data obtained by the method<br>proposed, changes of elastic anisotropy of core samples were studied and criteria-precursors of the destruction<br>of the near-shaft space during borehole drifting were found. They are mainly due to violation of the elastic<br>lithostatic balance of the geologic medium.<br>An analysis of the results of the whole set of petrophysical PT-experiments and the geologic-geophysical<br>information enabled us to assume possible changes of properties, composition and state of rocks at depth so<br>far not reached by drilling. We have also set up prognosed deep petrovelocity, geoelectrical and lithological<br>models of the Earth’s crust of the area of the Krivoy Rog over- and underthrust structure.<br>I sincerely thank all my researchers that participated in the investigations.

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/content/papers/10.3997/2214-4609-pdb.215.sbgf085
1999-08-15
2024-03-29
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.215.sbgf085
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