(Lithosphere)
Published by The Institute of Geological Sciences of the National Academy of Sciences of Belarus & The Belarusian Geological Society, Minsk, Republic of Belarus
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LITASFERA (Lithosphere) Published by The Institute of Geological Sciences of the National Academy of Sciences of Belarus & The Belarusian Geological Society, Minsk, Republic of Belarus |
Abstract: The original definition of the aulacogen type structures proposed by N.S.Shatsky described some general features noted in their structure and location, but did not considered their origin. The more recent definitions emphasized the rifting nature of aulacogens. The present paper shows that all the aulacogens of the old East European Platform and those developed at the Caledonian and Cimmerian-Alpine stages of the young Central European Plate evolution are branches of triple radial rifting systems. Some branches of these systems had lost their activity at various stages of rifting, while the others had experienced spreading and subsequently developed as geosynclinal depressions. Therefore, aulacogens usually join by their edges the recent folded belts that replaced geosynclinal depressions and show an asymmetrical structure due to the different intensity of tectonic movements, which decreases with increasing their remoteness from a geosyncline deep into the platform, Aulacogens inherit active structures of the older age (miogeosynclinal and fault zones) and differ from each other in their geological evolution history.
A.A. Sivoronov, A.M. Lysak, A.B. Bobrov, B.I. Malyuk
The lithosphere evolution in the Early Precambrian granite-greenstone terrains. Paper 1. Tectonic and formational complexes. pp. 11--18
Abstract: The major geodynamic role of granite-greenstone terrains in the general Precambrian evolution allows us to consider them as the distinct marker reflecting some transitional stage of the planet evolution. In the first section of the paper the main tectonic and compositional features of granite-greenstone terrains have briefly outlined, and some preliminary conclusions have been drawn regarding the specific character of different constituents of these peculiar segments of the Early Precambrian lithosphere. Within the typical granite-greenstone terrain vertical cross-section three lithotectonic complexes or megalayers can be distinguished. The lowermost and geologically oldest megalayer consists of charnockite-granulite rock associations. The overlying lithotectonic complex is universally known as the grey gneissic complex and is represented by amphibolite-plagiogranite rock associations. The last but not least megalayer is considered to be the most characteristic feature of the granite-greenstone terrains and consists of tonalite-greenstone rock associations. The greenstone belts were developed over the mature sialic crust as a result of diffuse spreading. The crustal conditions at that time were rather similar to those of the Phanerozoic epoch. In contrast, the ductile regime was characteristic of the early stages of the tonalite-greenstone megalayer development. However, the same regime was also achieved at the final stages of the granite-greenstone terrains evolution. Hence, these crustal domains may reflect the cyclic lithosphere activation and subsequent energy exhaustion.
A.A. Makhnach, N.D. Mikhajlov, I.L. Kolosov, L.F. Gulis, V.M. Shimanovich, O.V. Demeneva
Peculiarities of the sulfur isotopes behaviour in evaporite basins of the chloride and sulfate types. pp. 19--27
Abstract: The comparative analysis of the sulfur isotope behaviour in the chloride and sulfate type evaporite basins has been performed. The Upper Devonian deposits of the Pripyat Trough and the Permian deposits of the northern edge zone of the Caspian Depression have been chosen as the objects of studies. The sulfur isotopic composition of bedded anhydrites, as well as of sulfate minerals and pyrite dispersed in salt rocks has been studied. In addition, the carbon isotopes were investigated in carbonates from salts. It has been shown that the sulfate reduction which causes the accumulation of the isotopically heavy residual sulfate in evaporite brines hides the effect of crystallization fractionation and the influence of the light sulfur isotope intake with new portions of water in the chloride type basins. At this point, the sulfur isotopic composition of sulfate minerals in the chloride type basins becomes heavier from the gypsum stage to the chloride one. An opposite isotopic trend occurs in the sulfate type basins. The sulfur isotope ratio of pyrite formed at the chloride stage in the sulfate type basins is much lower in respect to the initial sulfate than in the chloride type basins. The differences are satisfactorily explained in terms of the openness degree of geochemical systems in respect to sulfate during the sulfate reduction: there is a closed system in the chloride type basins, and it is open in the sulfate type basins.
Abstract: Several world-wide known Pleistocene stratigraphic key areas and units have been derived from central Europe e.g. Saalian, Vistulian (Weichselian), Wartanian and Holsteinian. A thick marker bed of the late Elsterian glaciolacustrine silts and clays, overtain by sediments of the Holsteinian sea, is useful for stratigraphic and palaeogeographic correlation in central and eastern Europe. In Poland there is an extensive palaeogeographic and stratigraphic gap (0.9 to 1.2 million years long) between the boundary Tertiary/Quaternary and the first Pleistocene glaciation. Bioptimal interglacials e.g. Augustovian and Ferdynandovian can represent two separate interglacials, with a cold interval between them. Ice sheets of the Wartanian and the Middle Vistulian Glaciations could be more widespread in this country.
A.A. Arkhipova, I.V. Naidenkov
The Yurovichi and Pritoki strata of the amphibolite-gneissic complex of the Early Precambrian in Belarus. pp. 36--46
Abstract: Strata of the amphibolite-gneissic complex are widespread within the territory of the Smolevichi-Drogichin suture zone and Osnitsk-Mikashevichi volcanic-plutonic belt. These are similar in lithological composition, metamorphic grade and, probably, in age, but essentially differ in petrochemical composition, trace element contents and petrological features. All the above permits a differentiation the independent stratigraphic divisions: Pritoki strata within the suture zone and Yurovichi strata within the volcanic-plutonic belt. Rocks of the Yurovichi strata distinguished for the first time differ from those of the Pritoki strata in high alkalinity and alumina contents, high contents of "granitophile" (K, Rb, Ba, Be, Zr) and some siderophile elements, as well as in low contents of Fe, Ti, P, Ca, Sr, Cr and Mo. These distinctions depend largely on the composition of rock-forming minerals and, partly, on the amounts and assosiations of auxiliary and accessory minerals in rocks. The origin of rocks of the Pritoki and Yurovichi strata is also different: volcanogenic and volcanogenic-sedimentary, respectively. Many geochemical features typical of the Yurovichi strata rocks (high content of "granitophile" elements and volatile components, high alumina content of biotites, etc.) are peculiar to rocks of other complexes widespread within the volcanic-plutonic belt, which may be due to regional migmatisation processes occurring with the intrusion of the Proterozoic Mikashevichi complex. On the other hand, some geochemical features common to many complexes of the Pripyat Trough basement (high content of Sc and some siderophile elements in rocks and Zn in rock-forming minerals, low content ofFe, Cu and several other elements) most likely suggest an originally different geochemical characteristics of the basement of the Smolevichi-Drogichin suture zone and the Osnitsk-Mikashevichi volcanic-plutonic belt, that are obviously related to different geochemical provinces. As regards the formations of the Pritoki and Okolovo series widespread within the Smolevichi-Drogichin suture zone and similar in metamorphic grade and, probably, in age, these also show essential differences in the rock geochemical features, trace element composition of minerals and the type of the ore and accessory mineralisation.
S.M. Obrovets, E.A. Vysotsky, B.G.Medvedeva, L.A, Demidovich †, L.F. Korobchuck
Paleorelief of the Lower Famennian basin bottom in the southern part of the Pripyat Trough. pp. 47--55
Abstract: Lithological and facies fields were distinguished in the Lower Famennian Kuzmichy, Igrayevo, Visha, Turov, Drozdov, Petrikov, Borichev deposits from the changes in the thickness, lithological composition, structural and textural features of rocks. Horizontal transitions and boundaries of lithofacies fields were controlled by synsedimentary faults, benches and sedimentary barriers. The paleorelief of the basin bottom in the Pripyat Trough southern part has been reconstructed at the following stratigraphic levels: Kuzmichy, Igrayevo, Visha, Turov, Drozdov, Borichev beds, Petrikov horizon. The boundaries of the lithofacies zones used as a basis for paleogeomorphological reconstructions were controlled by synsedimentary faults, benches and sedimentary barriers. Positive (islands, uplands, hills, island slopes) and negative (valleys, deltas) paleolandforms have been distinguished in the sea basin floor. The dynamics of evolution of some paleolandforms - East-Vystupovichi, South-Valavy, West-Valavy submarine valleys, Velikoye Pole - Lipliany hills, Nikolayev - Valavy upland, Vystupovichi and Valavy deltaic complexes during Early Famennian time has been traced. Positive and negative forms of the bottom paleorelief were recognized from investigations carried out. There are islands, island slopes, submarine rises and submarine ridges, deltaic paleotracts. Paleovalleys were the main negative forms of the paleorelief, Paleomorphologically, oil traps at the intersalt section exposed were controlled by the paleorelief of the sedimentary basin bottom manifested as traps localization distinct paleomorphological elements: deltaic complex, paleovalley.
N.N. Levykh, N.V. Veretennikov
Dark-coloured minerals as indicators of deep facies rocks from the Zhlobin field diatremes. pp. 55--62
Abstract: Partially and completely intact dark-coloured minerals of volcanoclastic alkali-ultrabasic rocks from diatremes and involved crystalline rock xenoliths have been studied mineralogically and geochemically. It has been revealed that among pyroxenes chrome augites are dominant, and chrome diopsides are less abundant, Wide variations of the chemical composition of augites were used to recognize their xenogenous origin mainly from the lower crustal part. Chrome diopsides are thus assigned to the upper mantle rocks. Ferruginous hornblendes (hastingsites) dominante among amphiboles, and ordinary hornblendes formed at the greater depth are less common. Mica is qualified as an important distinctive mineral. Among micas besides essentially or completely xenogenous biotite and muscovite, there are phlogopites, ferriphlogopites and tetraphlogopites. Such a diversity of micas is apparently due to their different genesis and origination, in some cases, as a result of metasomatic transformation of pyroxenes, amphiboles and garnets. Decreased amounts of alumina and titanium dioxide were noted in some phlogopites, as concentrations of the total iron increased, which is indicative of favourable conditions for the evolution of both kimberlites, and lamproites. In general, a set of dark-coloured minerals from diatreme rocks and involved xenoliths describes their enclosing rocks as the upper mantle formations occurring at small depths and represents a pyroxene-pyrope-ilmenite association by the classification of indicator minerals of kimberlites and lamproites.
L.N. Taran, S.V. Bogdanova
Zoning garnets from the metasedimentary granulites of the interior part of the Belarus-Baltic granulite belt. pp. 62--70
Abstract: The 200 km wide Belarus-Baltic Granulite Belt (BBG) extending in SW-NE direction for about 1000 km from southeastern Poland across the northwestern part of Belarus consists of lensoid granulite units separated by steep zones of faulting, retrogression and blastomylonitization. Metasedimentary granulites containing the poikiloblastic garnets have been examined to assess the P-T evolution of the interior part of the BBG. The study was focussed on the heterogeneity of large garnet poikiloblasts in regard to Fe, Mg and Ca, and textural-compositional relationships of the garnet with other minerals. From chemical mapping and profiling of garnet, the P-T evolution was subdivided into two stages of metamorphism. A prograde stage recognized in a metagraywacke is represented by inclusions of plagioclase, biotite and quartz in the garnet cores and is marked by increasing both the temperature and pressure from 540 to 620°C and from 3 to 6 kb. The outer cores of the garnet from the metagraywacke, as well as cores of the anatectic garnets record peak metamorphic conditions of 750-760°C at 7.5-8 kb. A retrograde stage following the peak metamorphism is indicated by P-T conditions dropping to 530-540°C at 3.5-4.5 kb. The obtained P-T data together with the magmatic history in the belt suggest that a crustal thickening event with changes of P-T conditions from 540-570°C at 3--4 kb to 750°C at 8.5 kb occurred before 1800 Ma. Postcollisional thinning of the crust ca 1790 Ma ago was associated with emplacement of numerous bimodal mafic to granitic intrusions which probably caused the granulite-facies metamorphism at depths of 25-30 km. Subsequent cooling and uplifting were continued up to ca 1700 Ma ago.
A.M. Pap
Metasomatites in the Precambrian of Belarus and their importance in mineral prospecting. pp. 70--76
Abstract: Most of endogenic mineral deposits originated due to metasomatism. Their formation was usually preceded by metasomatic changes of the lateral host rocks. Each ore field is associated with certain processes of metasomatism. A study of evidences of metasomatic processes occurring under complicated geological and thermodynamic conditions may be useful in judging about mineral potential of one or another part of the Earth's crust. Zones of metasomatic changed rocks cover always larger areas, than their enclosed ore-bodies, Therefare rocks transformed by metasomatism, which is associated with ore formation should be considered as an obvious ore hunting evidence. Metasomatic changes of rocks are always due to solution fluids and their mobile components, some of them being ore-forming ones. Along with temperature and pressure such a thermodynamic feature as the acid-ity-alkalinity, conditions play a decisive role in the evolution of these solutions influencing the course of metasomatic and ore deposition processes, as well as the replacement of mineral assemblages. Contact leaching is superimposed over biosomatic and contact-infiltration changes of the lateral rocks. Depending upon the lateral rock composition and chemical elements contained in hydrothermal and other solution fluids such types of fissure metasomatism, as dolomitization, ankeritization, sideritization and quarzitization are distinguished. In some cases these are associated with complex ore occurrences. Minerals of the lateral rocks are replaced by sericite, chlorite, low-temperature orthoclase and some others depending on the acid-ity-alkalinity media of solutions. These minerals may serve as hunting evidences of ore occurrences that had formed against a background of altered rocks. Among host rocks favourable for the accumulation of copper, gold, molybdenum and other metals there are beresites, listwanites, propilites, humbeites, secondary quarzites, sericite-quarzic metasomatites, rarely chiorite-carbonate rocks. Scarn, albitite, greizen, hydrothermal, humbeitization, pyrite genetic types caused by corresponding lateral rock changes are characteristics of molybdeum fields. Genetic and spatial association between metasomatism and ore accumulations should be regarded as an important evidence for ore deposit prospecting.
N.Ya. Yashchenko, V.V. Shekhotikin
New data on the tectonomagmatic history of the Ukrainian Shield (Ingul-Ingulets region). pp. 76--84
Abstract: The magmatic rock dated with thermoisochronous Pb-Pb method made it possible to identify for the first time Late Archean intrusive complexes (formational and time analogues of the Middle Dnieper magmatic complexes) in the Ingul-Ingulets region of the Ukrainian Shield. They are the following: diorite-tonalite-plagiogranitic (an analogue of the Sura one, 3100-3000 Ma), granodiorite-graniric (an analogue of the Demurian one, 2930-2900 Ma), basic complex (an analogue of the South-Krivoy Rog one, 2800-2700 Ma). This enabled us to prove the Late Archean age of the Ingul-Ingulets series, to reconstruct the geodynamic regime in the Late Archean and Proterozoic; to show, specifically, that the global structural reconstruction of the region was caused by an activation at about 2800-2700 Ma (Kenoranian orogeny). The formation of the largest tectonic structures of the Ukrainian Shield (the Krivoy Rog-Kremenchug fault zone) is associated with it. In the Proterozoic four stages of the tectonomagmatic activation were evidently shown in the Ingul-Ingulets region as distinct from the Middle Dnieper one: 2400-2300 Ma (the Near-Ingulets complex of cordierite-raremetal pegmatoidal granites); 2100-2000 Ma the Eburnean orogeny, large intrusions of the New-Ukrainian - Kirovograd complex, high-temperature metamorphism, formation of gneissic rock strata); 1800-1700 Ma (the Karelia orogeny, the Korsun-Novy-Mirgorod complex of rapakivi granites); 1500-1400 Ma (the Gotian orogeny, raremetal granites, basitic dikes).
T.V.Kaulina, M.M.Bogdanova
The main stages in the development of the northwestern White Sea region: U-Pb isotopic data. pp. 85--97
Abstract: In the northwestern White Sea region which is a fragment of the White Sea-Lapland Belt the main magmatic associations and processes representing different stages of the belt evolution have been dated.
Zircons from rocks of the islands and shore of the Kandalaksha Bay of the White Sea: the Tolstik Pen-insula, the island of Krivoy (the Kovdin Archipelago), Nikolkin, Krivoy and Gorely (the Poria Bay) and the Shombach Cape have been studied mineralogically and isotopically.
1. Tonalite gneisses which are widespread in the northwestern White Sea region and were previously thought to represent the oldest Early Archean crustal components in the Baltic Shield have been studied within the Tolstik Peninsula and Krivoy Island (Kovdin Archipelago).
The tonalite gneisses are of at least two different age groups. The oldest tonalite gneisses I are strongly migmatized. They are cut by syntectonic bodies of unmigmatized tonalite gneisses II.
Magmatic zircons with fine euhedral internal zoning from tonalites. I paleosome and analogous zircons from tonalites II and tonalites of the Krivoy Island were investigated. The zircons showed discordant ages of 2761± 10, 2695± 10 and 2717± 7 Ma, respectively.
So, the tonalite gneiss association is heterogeneous and shows a multistage evolution history.
2. Rifting at the Proterozoic stage of the White Sea-Lapland Belt evolution was accompanied by the formation of the anorthosite-gabbro-diorite intrusions. The age of monomineral anorthosites is 2.45-2.46 Ga (Mitrofanov et al., 1993; Frish et al., 1995). Isotopic data for metagabbronorites and gabbro-anorthosites of the Tolstik Peninsula and for diorites of the Nikolkin Island (Kolvitsa Belt) are presented below.
The 2443± 10 Ma magmatic zircon age for the Tolstik metagabbro massif is identical within error to that obtained earlier by Bibikova E.V. (Bogdanova, Bibikova, 1993) for this massif (2434± 7 Ma). Metamorphic zircons generally have a 207Pb/206Pb age of about 2409 Ma. The age of gabbro-anorthosites is 2444± 7 Ma.
In the Kolvitsa Belt, diorite dikes of the Nikolkin Island were the subject of geochronological studies. Diorites have xenoliths of monomineral anorthosites 2.45-2.46 Ga in age.
Magmatic zircons from diorites showed a discordant age of 2436± 6 Ma interpreted as the time of diorite crystallization. The 1919± 18 Ma metamorphic zircon nearly concordant age provides an estimate of the time of tectonic-magmatic activation of the crust under the amphibolite facies conditions at the Svecofennian stage of the White Sea-Lapland Belt development.
Therefore, different White Sea-Lapland Belt structures show a simultaneous magmatism resulted in an anorthosite-gabbro-diorite congenetic series: gabbro from the Tolstik Peninsula at 2443± 10 Ma; diorites from the Kolvitsa Belt at 2436± 6 Ma.
3. Three types of microcline granites were studied at the Tolstik Peninsula: microcline veins in tonalite gneisses II, microcline veins in microcline porphyraceous granites with an age of 2405± 20 Ma (Bogdanova, Bibikova, 1993) and microcline aplite-like granites.
Magmatic zircon fractions yielded U-Pb ages of 2266± 12 Ma, 2376± 11 Ma (concordant age) and 2365± 12 Ma, respectively. These ages are interpreted as dating the igneous crystallization of the rocks.
Thus, in the northwestern White Sea region two stages of granitic K-magmatism were recognized and dated at 2.41-2.38 Ga and 2.27 Ga.
4. In the Poria Bay zone rock associations from the Krivoy (enderbite-gneisses, enderbite migmatites, subalkalic granites) and Gorely (a plagiogranitic pegmatite vein) Islands were investigated. Enderbite leucosomes cut the more ancient metamorphic banding of enderbite-gneisses. The development of the leucosomes was due to the high-T granulite metamorphism (Bogdanova, 1984).
Magmatic zircons from enderbite-gneisses have thin rims of metamorphic overgrowth (amounting to about 10% of the total volume of the grain) which could not be removed because of a small grain size ( < 75 mm). The age of 2521± 20 Ma obtained for these zircons represents therefore an average value of the core and overgrowth datings. The date of 2521± 20 Ma may thus be a minimum estimate of the intrusion age of enderbites. The metamorphic overgrowth is probably due to the high-P granulite metamorphism which was the earliest metamorphic event for the enderbite-gneisses. An approximate age of the first stage of the high-P metamorphism of the Lapland Granulite Belt is 2.4 Ga (Balagansky et al., 1995).
Zircons from enderbite leucosomes define a three fraction discordance with the upper intercept at 2181± 8 Ma, which is interpreted as the time of the enderbite migmatite development under the high-T granulite metamorphism conditions.
At the same time enderbite-gneisses contain zircons similar to those from the nearest subalkalic granitic intrusions. An age of these zircons is 2268± 7 Ma. An age of zircons from the subalkalic intrusions is 2289± 20 Ma. The host rock may contain zircons originated under the influence of the intrusion, and these zircons are identical morphologically and in age to those from the intrusion (Levchenkov, Zinger, 1995).
A completion of endogenic processes in the White Sea-Lapland Belt is evidenced by post-consolidation pegmatites which cut all rock associations in the region.
An age of the pegmatite vein crystallization (the Gorely Island) is 2056 ± 3 Ma.
5. In the Umba region zircons from paragneisses were investigated. An age of metamorphic zircons is 1901± 29 Ma which is identical to that obtained earlier by Bibikova E.V. (Tygarinov, Bibikova, 1968). Detrital zircons show a Pb-Pb age of 2167± 47 Ma.
Yu.M. Obukhovskiy, L.L. Grigorevich
Peat-mire complexes of Belarus. pp. 98--104
Abstract: To study the natural mire complexes and their anthropogenic dynamics the concept of peat-mire complexes (PMC) has been proposed, according to which they are considered as zoned multistage systems of various complexity, involving peat deposits, shallow bogs, bogged and waterlogged lands, as well as slopes of local watersheds that are related to each other by the common hydrological regime and similar course of exogenous processes. The vertical layers conforms to the horizontal zones of morphogenesis. There are technogenic lows of soil, disappearance of peat deposit, transformation of nanorelief, simulation of ecogenic processes on slopes. PMC includes a basin of mire within local watersheds. The Belarus PMC classification has been developed including the formation of 15 classes and a number of subclasses. There are among them closed depressions of glacio-lacustrine and morainal plains, drainage depressions of morainic relief, drainage depressions of glacio-lacustrine and morainic plains, suffosion depressions; slopes of aquaglacial plains, glacioalluvial lowlands, terracesabove floodplain, oxbow lakes; flat flood-plains; erosional floodplains pverlying moraine; ridged floodplains; through valleys; ravines. A range of activities to be solved using PMC landscape classification was outlined. There are both traditional issues of litho- and hydroindication, geomorphological, geological, geodynamical, retroindicational, ecological and methodical aspects. The necessity of working out new methods of studing mire landscapes is associated with their increased ecological importance under technogenesis conditions,
Abstract: The correlation of the gravity anomalies with geological units of different age has revealed some regular features in the time dynamics of the gravity field. It is believed that it is necessary to compile and analyze the structure-density models describing the dynamics of the gravity field during various tectonic processes that may be useful to understand and explain these regular features. A concept of the Pripyat Through tectonogenesis is discussed below. It is based on the formation of some plume-fluid energetic source (an asthenospheric lens) which was formed in the asthenosphere beneath its ancient suture zone. An energy of the source is mainly spent for the transformation of the material in the lower part of the lithosphere into the plastic state and also for the formation of the basaltic layer of melts at the eclogitization level. It was assumed that the crust of the Pripyat Trough is characterized by ductile properties. Under an external stress exceeding the rock rupture strength limit of to = 107--108 dyn/cm2 the crust is subject to brittle breaking. The lower part of the lithosphere below 80-100 km is under such temperature and pressure conditions when the lithosphere material of the layer above the asthenolens is transformed into the plastic state under the external stress exceeding this hear rocks strength limit to = 107 --108 dyn/cm2. The following stages of the Pripyat Trough formation have been distinguished:
-formation of an asthenolith in the asthenosphere during the time interval tk -- to,
- the heat and mass transfer of the fluid-enriched asthenolith material through the lower ductile lithosphere part to the level of the mantle material ecologitization and formation of the basaltic melt layer during the time interval tb -- tk,
- intrusion of basaltic melts and fluids into the upper elastic-rigid part of the lithosphere and formation of the petrological structure of the crust and subcrustal layer during the time interval tc --tb,
- formation of the graben in the upper part of the crust before the tr moment and the development of isostatic processes which complete the stress relaxation caused by an "explosion" of the asthenolens.
To study the gravity field dynamics during the Pripyat Trough tectonogenesis the time-levels of the lithosphere and asthenosphere structure-density state which correspond to the above stages have been considered.
S.V.Golobokov, I.V.Dankevich, G.I.Karatayev
Density Models of the Earth's Crust in Belarus. pp. 113--125
Abstract: When analysing a set of geophysical data obtained for the Ukrainian Shield in the context of its block tectonic structure the authors have revealed the following regular features: each block is characterized by specific geophysical homogeneity, blocks having different evolution history show different geophysical properties, blocks grouped into a succession reflecting the Earth's crust development are characterized by regular changes of geophysical parameters. Contact zones between blocks are deep faults penetrating throughout the crust into the mantle. A successive geophysical classification of the Earth's crust was suggested on this basis using geophysical data available for Belarus and the adjoining areas of Russia, according to its deep structure types and reflection in the geophysical fields: (A A geophysical type was assigned to crustal blocks with known deep structure. The rest of the territory within the East European Platform west was divided into zones according to crustal types and using the ideas and methods of computer image discernibility with a complex of geologic-geophysical mapping data, and a corresponding map was compiled (Fig.1). The computer zonality has shown that narrow bands of "unclear discern" with a width of 30-40 km correspond to zones of junction of crustal blocks of different geophysical types within the Ukrainian Shield. This fact was used as a criterion to distinguish fault zones in the territory of Belarus as well. Some typical patterns of reflection of such zones in the gravity field were observed. The first pattern: commensurable gravity minima linearly stretched along the whole strip, or a considerable part of its length with an intensity as high as 10-15 mGal correspond to the "Sebezh-Rossony", "Obialiai-Ignalina", "Vasilevichi-Khoiniki-Komarin", "Mogilev-Mstislavl", "Soligorsk-Kamenny Borok" zones. The second pattern: the "Grodno-Ignalina" strip is described by a narrow relatively lowered linear zone located in between positive gravity anomalies. A chain of local minima of the gravity field with an intensity about 5-15 mGal was observed on the background of this zone. The third pattern: "Uvarovichi-Klintsy", "Telekhany-Domanovichi", "Kamenets-Belozersk" linear strips are reflected by latitudinal gradient zones of the gravity field representing transitional areas between vast positive and negative fields, which isolines run along the considered strips of "unclear discern". The fourth pattern: "Vidzy-Begoml-Bobr", "Lyubeshov-Ivanovo", "Turov-Zhitkovichi", "Usvyaty-Mstislavl", "Obol-Bobr", "Komarovichi-Rechitsa", "Ignalina-Polotsk-Usvyaty", "Kamenets-Sokulka-Suvalki" strips are traced by a chain of local gravity minima of different mainly low intensity accompanied by poorly distinguished local maxima. The fifth pattern: the "Ivatsevichi-Korelichi-Begoml" strip is characterized by a chain of alternating local gravity maxima and minima of different intensity. Almost all the strips of "unclear discern" are characterized by a chain of local maxima and their associated minima often lineary elongated that suggests their intrusive origin. The one exception is a latitudinal strip along the line "Kamenets-Domanovichi-Klintsy" located within a deep-seated basement area and, therefore, almost not reflected in the magnetic field. In the most cases the locally distinguished gravity minima of different intensity and size correspond to sizes of nodes representing zones of strip intersection. Only the node of intersection of the "Mogilev-Mstislavl", "Obol-Bobruisk", "Soligorsk-Kamenny Borok" strips is characterized by an intense gravity maximum of 20 mGal. The pattern of geophysical fields within strips at junction of different crustal types shows that these strips are rather spaced, probably strongly fractured in sites where the magmatism was developed. The described features of strips of junction of crustal blocks of different crustal types corresponds to the criteria of tracing deep faults zones from potential geophysical fields existed in the other regions. Therefore, we have the ground to interpret the linear strips of "unclear discern" of an area of junction of blocks of different geophysical types as zones of deep faults. To estimate their depth in a number of profiles cutting such zones the density models have been compiled. Data obtained are presented in Table 1 showing the structure of the Earth's crust and density of its major layers at the junctions of crustal blocks showing by different types of their deep structure. These data clearly suggest that the studied group of deep faults is characterized by the deconsolidated crust throughout its whole thickness. The investigation of density models of the Earth's crust along the described profiles permits the following conclusions to be made. Firstly, the zones distingushed in the Belarussian region from a set of geologic-geophysical data on the basis of the developed geophysical types of the Earth's crust A<AB<B<C<CD<D<E, F and G correspond to the pattern of distribution of the crustal material density. Secondly, the deep origin of faults separating crustal blocks of different geophysical types was proved. These fault zones could be classified as penetrating faults. They are characterized by deconsolidated crustal material throughout the crossection of the Earth's crust relative to the neighbouring crustal blocks of different types of the crustal deep structure and represent fissured zones.
A. V. Gavrilov
Comparative geophysical characteristics of the pipe fields within the Zhlobin saddle and adjacent areas of Belarus. pp. 126--132
Abstract: Some features of the crust deep structure considered to be the kimberlite-controlling factors have been discussed in the paper. The action of these geologic-geophysical factors in the region under exploration has been studied. It was noted that the fields of pipe abundance are confined to the nodes of intersection of deep fractured zones. Diatrems revealed have been divided into fields. Comparative geophysical characteristics of the pipe fields located within and near the Zhlobin Saddle (Zhlobin field, Uvarovichi field and probable Svetilovichi field) have been given. The Main features of magnetic and gravity fields have been described. It was revealed that the well-known factors affecting the pipe distribution are clearly reflected in magnetic and gravity fields, but do not appear in the results of electric-geochemical and electric exploration in the territory under consideration. Geophysical parameters of both well-known diatrems, and those which exploration is still carried out are given. Anomalies revealed and justified by geophysical evidences in the area near Svetilovichi have been described. The prospects of discovering new diatrems in the region have been analysed.
Abstract: On the base of pedogeochemical and palinological study dayly (actual) alluvial-dern and Middle-Holocene baried soils are staked, that river sediment accumulation, forced during the Subboreal period and entailed the burial of Middle-Holocene darkcolor soil, have been retarded during SA-3 and pedogenesis have been started. The pedogenesis is accompanied by sediment accumulation in the conditions of upwards growing of soil strata. The lower part of the latter is loam of the SB-SA-2 and upper one is sandy loam of the SA-3-a, SA-3-b, SA-3-c and SA-3-d, which accumulate synchronously with soil formation. On the whole pedogenesis and sedimentogenesis, synchronous witht hem, are elapsedin agrisive geochemical environmental: oxydative - redaction potenzial fluctuate from 240 to 410 mV, pH chage from 4.2 to 5.4, hydrolitic acidity is average 3.5 mgr/ekv on 100 gr soil. Under geochemical data (humus content, values of (SiO2:R2O3, Fe2O3:FeO, Zr-V and V-Ti) the layers ar marked; pedogene processes are manifested much more degree in layers of SA-3-a, SA-3-b, but sedimentogene ones - in SA-3-c, SA-3-d. The distribution of summary accumulation of microelements, of Cu and Ni contents differentiate the intervals with four concentration levels, which corresponde phases of SA-3. It is occur the weakening of silt temakiny by biopedogeochemical processes during SA-3-d. The palinological and geochemical data clearly are correlated and reconstracte the peculiarities of paleogeographical changes, including linked one with technogenesis.
L.D.Lebedeva
Geologic-hydrogeological criteria for selecting places for the production and consumption waste disposal in Belarus. pp. 142--145
S.A.Akudovich
Total geological resources of metals in the subsurface brines of the Pripyat Trough. p. 146
CHRONICLE. pp. 147--154
JUBILEES. pp. 155--160
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