THREE-DIMENSIONAL DENSITY MODEL OF THE UPPER CRUST AT THE JUNCTION OF THE LOSEVSKY AND DONSKOY TERRANES (VORONEZH CRYSTALLINE MASSIF)

The results of detailed three-dimensional density modeling of the upper crust of the area located in the southeastern part of the Voronezh crystalline massif at the junction of the Losevsky and Donskoy terranes and, partially, the Vorontsovsky terrane are presented. The resulting model was built based on the inversion of local anomalies of the gravity field into anomalous density values, taking into account all available geological and geophysical information. The field inversion was implemented within the framework of the starting model developed on the basis of the regional density model and corresponding gravitational field of the East European platform lithosphere, generalized information on the density of rocks of the sedimentary cover and crystalline basement, the thickness of the «gravitational» layer obtained by statistical analysis of the anomalous field, and geological data and topography. The resulting model shows density distribution of the crystalline basement rocks to a depth of 16 km, and provides thus fundamentally new information about the geological structure of the upper crust of the area. The model makes it possible to trace geological objects, which are most expressive in terms of density, at deep levels, and allows interpreting the relationship between the Losevsky and Donskoy terranes in the upper-middle crust. The consistency of the model and observed gravitational fields indicates the reliability of the obtained results.

EAST EUROPEAN PLATFORM. RUSSIAN PART

It is reported that 22 stationary seismic stations, 2 arrays and 7 local seismic stations, located in the area of Novovoronezh and Kursk nuclear stations, monitor seismicity of the Russian territory of the East European platform (EEP). A new station Belogornoe with high registration class has been opened, which also belongs to the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty (IMS CTBTO). The results of the microseismic noise study at the Pulkovo network stations and assessment of maximum distance of earthquake registration in the Voronezh crystalline massif are presented. In 2014, relatively strong earthquakes with М3.0 were not recorded on the Russian territory of the EEP. Weaker natural seismicity with M≤2 was recorded in Karelia and the border areas with Finland, near Kandalaksha Bay, near the Khibiny Massif on the Kola Peninsula and on the territory of the Voronezh Crystalline Massif. Observations of local networks near nuclear stations are aimed at updating the information on seismicity previously considered as an aseismic territory of the EEP. Man-made events were recorded in permanent quarries, the most powerful of them (M=3.1–3.3) were produced in the quarries on the territory of the Kursk magnetic anomaly.

Revisiting stratigraphic complexes and regional stratigraphic scheme of the lower precambrian of the Ukrainian shield Article 2. Correlation of complexes of ukrainian and other shields of North Eurasia

The second article discusses the 5 main types of stratogenic metamorphic complexes found in the East-European and Siberian platforms: 1) granulite-gneissic; 2) amphibolite-gneissic; 3) greenstone; 4) ferruginous-siliceous-schistose (metavolcano-chemo-terrigenic) 5) gneiss-schistose (metacarbonaceous-terrigenic). The types of complexes, in addition to the fact that they differ in the degree and type of metamorphism, also have different geologic-formational composition. These complexes are seen as the largest regional stratigraphic subdivisions in all regions of the Early Precambrian. They are represented with varying degrees of completeness on the Aldan-Stanovian, Anabarian and Baltic shields and on the Voronezh crystalline massif. The most complete stratigenic metamorphic complexes are developed on the Ukrainian and Aldan-Stanovian Shields. The complexes of the various regeions are mutually correllated between themselves and the Ukrainian Shield based on them corresponding to the types of stratogenic metamorphic complexes. The similarities between the complexes across different regions are to most researchers evidence not only of similar conditions of the formation of same-type complexes, but also, most likely, their conformance to identical quasi-synchronous stages in the development of the Earth’s core. Based on the results of both articles of the cycle, it is concluded that the largest divisions of the current Chronostratigraphic Scheme of the Early Precambrian of the Ukrainian Shield, which are shown in it as “series”, deserve either the transfer to the rank of “stratigraphic complexes” or the inclusion in the complexes by uniting series. Combining of the series concern to granulite-gneiss complexes that need to be renamed in the updated stratigraphic scheme. For other complexes, for the sake of inheritance with the previous schemes, it is advisable to preserve the geographical names of the series.

Mesoarchean silicic volcanics of the Kursk block, Voronezh crystalline massif: composition, age and correlation with the Ukrainian shield

Rhyolites and basite rocks are present in the Archaean greenstone belts of the Kursk Domain (KD) of the East Sarmatia. The rhyolite age is 3122 ± 9 Ma (zircons, SIMS). A positive εNd (3122) = + 0.9 for rhyolites and their Sm-Nd model age ТNd (DM) = 3300 Ma as well as the age of the inherited zircon (3250 Ma) testifies to the participation of the more ancient crust component in the formation of rhyolite magmas. In geochemistry, rhyolites are very close to the TTG of the KD with an age 2.96-3.03 Ga. In the Middle Dnieper granite - greenstone area there are rhyolites and dacites with an age of 3.12 Ga with εNd (T) = + 0.6 - (+1.2) and very close geochemical characteristics. Thus, the hypothesis of a common geological history of the eastern part of Ukrainian Shield and KD in Mesoarchean is confirmed.