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Alkaline rocks of the Ukrainian Shield: Some mineralogical, petrological and geochemical features

Ponomarenko A. N., Kryvdik S. G., Grinchenko A. V.

Mineralogia

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2013

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Vol. 44, iss. 3/4

115--124

EN

The Ukrainian Shield (USh) is a typical province of Proterozoic alkaline magmatism where about 50 massifs and occurrences of alkaline rocks and carbonatites have been found. In spite of the wide distribution of Devonian basaltic- and alkaline magmatic rocks in the Dnieper-Donetsk depression adjacent to the USh, and in a marginal zone of the USh adjacent to folded Donbass, only alkaline rocks of Proterozoic age (1.8-2.1 Ga) that have been identified in the central interior of the USh. Some discrete bodies of 2.8 Ga subalkaline rocks also occur in Bogdanivka massif (Azov area). Occurrences of both Proterozoic (prevailing) and Phanerozoic (Devonian) alkaline rocks and kimberlites are only found in the eastern part of the USh (Azov area). Kimberlites in the central part of the Ukrainian Shield (Kirovograd region) are also of Proterozoic age (ca 1.8 Ga). It is this predominance of Precambrian rocks that makes the USh so different from other alkaline provinces where Phanerozoic alkaline rocks and kimberlites commonly prevail over Precambrian rocks. The lack of Phanerozoic alkaline magmatism on USh is poorly understood. Two main complexes of alkaline rocks - alkaline-ultrabasic (carbonatitic) and gabbro- syenitic - are distinguished in the USh. There are also rare occurrences of rock types such as alkaline- and alkaline-feldspar granites that may represent one separate alkaline-granite complex. Alkaline rocks present in the Eastern (Azov) province and in the Western province display essentially different geochemical character. Those of the Eastern province show characteristics typical of alkaline-ultrabasic rocks (e.g. high contents of incompatible rare elements 116 such as Nb, REE, Zr, Y, Sr, whereas those in the Western province are characterized by low contents of Nb and Zr, and REE in some cases. This fact is interpreted as reflecting different geodynamic conditions of their origin. The Eastern rocks were formed in rift settings, the Western rocks in crustal compressional settings (collision, subduction). Various mineral deposits of phosphorus (apatite), niobium, REE, yttrium and zirconium, including unusually rich ores of REE, Y and Zr (Azov and Yastrybetsky) are associated with the alkaline rocks and carbonatites of the USh.

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Density-velocity relationship in the upper lithosphere obtained from P- and S-wave velocity models along the EUROBRIDGE'97 seismic profile and gravity data

Kozlovskaya E., Janik T., Yliniemi J., Karatayev G., Grad M.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 4

397-424

EN

Traditionally, joint interpretation of seismic refraction and wide-angle reflection data and gravity data is based upon a well-known correlation between seismic P-wave velocity and density proved by numerous laboratory investigations of elastic properties of crustal rocks. One of the problems connected with this approach is that rocks with high content of calcium-reach plagioclase have higher P-wave velocity and do not satisfy the common density-Vp relationship. That is why joint interpretation based upon any conventional relationship between density and P-wave velocity cannot be applied to wide-angle profiles across large anorogenic rapakivi-gabbro-anorthosite massifs composed of rocks with high content of plagioclase. The problem can be solved if both P- and S-wave velocities are used to calculate the density model. The results of laboratory studies of rock properties demonstrate strong correlation between density and S-wave velocity. Moreover, the isotropic S-wave velocity seems to be generally more correlated to density than the P-wave velocity and less affected by high content of plagioclase. In spite of that, the known relationships connecting density to S-wave velocity or to both P- and S-wave velocities are very seldom used for joint interpretation of seismic and gravity data. The main reason for this is a lower quality of S-wave arrivals in explosion seismology, which makes it difficult to obtain reliable S-wave velocity models. In our paper we present the results of joint interpretation of seismic and gravity data collected along the EUROBRIDGE'97 wide-angle reflection and re-fraction profile in the Ukrainian Shield, where the absence of thick sediments made it possible to obtain both P- and S-wave velocity models. To calculate the density model along the EUROBRIDGE'97 profile we used a method of gravity data inversion, in which the density model was parameterised by the relationship connecting density to both P- and S-wave velocity models. Such a parameterisation makes it possible to obtain the relationship between density and seismic velocities by inverting the gravity data. As a result, non-linear and scattered relationship between density and seismic velocities was obtained for the EUROBRIDGE'97 profile. Analysis of the relationship demonstrated that the reason for this scattering is difference in density-velocity relationships for large-scale geological units crossed by the profile. In order to explain this difference, we compared the relationship between seismic velocities and density in three major geological units crossed by the EUROBRIDGE'97 profile with the petrophysical data from the Ukrainian Shield and other selected Precambrian areas. We demonstrated that the deviations from the averaged density-velocity relation-ships can be explained by specific mineral composition of rocks resulting from different age and conditions of crust formation. We showed how the analysis of density-velocity diagrams can be used to restrict the composition of the crust and, in particular, the composition and metamorphic grade of the lower crust.

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Applying the horizontal spatial gradient method for the deep conductivity estimations in the Ukraine

Logvinov I.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 4

567-573

EN

The analysis of the long-period magnetovariation data obtained in the Ukraine and from the project PREPAN-95 are presented. The response functions have been estimated for the harmonics of daily variations for the periods of 4-24 hours using the horizontal spatial gradient method of the magnetic field components. These results together with data of the nearest geomagnetic observatories have given the possibility to compare the mantle geoelectrical structures for three different tectonic regions in the Ukraine. The greatest difference is observed between the Ukrainian shield and the Carpathians together with the Tornquist-Teisseyre zone.

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Seismic structure of the crust-mantle transition zone of the Ukrainian shiels

Starostenko V., Kharitonov O., Tripolsky A.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 2

185-201

EN

The Ukrainian shield is one of the largest heterogeneities of the East European Platform. The deep seismic sounding results indicate a blocked layred structure of the shieldsand enabled us to separate several long submeridonal crustal blocks, notably differing from each other in thickness, which are cut deep falts of mantle origin. The geologic and geophysical features of these blokcs suggest that they belong to protoplatform structures with 38-51 km thick crust and protogeosynclines with Moho-discontinuity depth to 65 km. An analysis of dynamic characteristics of reflection waves shows that within the protoplatform blokcs the Moho-discontinuity is mainly a sharp boundary of the first order with longitudinal waves velocity contrast corresponding to the basic-ultrabasic rocks contact. In the protogeosynclinal systems, a 3-9 km thick crust-mantle transition zone is distinguished. By using of combinated kinematic-dynamic analysis for the Ukrainian shielld, several of acoustic models of the crust-mantle transition zone were distinguished. The nature of this zone may be either a gradual transition from mafic to ultramafic rocks or its origin may be results of the underplanting.