A large anticline structure occurs in the western part of the Azov Domain of the Ukrainian Shield. It is composed of rocks of the Mesoarchean (3.2-3.0 Ga) granite-greenstone association and relics of an older basement. The anticline is divided into two parts by the Bilotserkivka structure of sub-latitudinal strike. The northern part includes the Huliaipole and Remivka blocks, and the southern part comprises the Saltycha anticline. The U-Pb age of plagiogneisses of the Lantsevo anticline of the Bilotserkivka structure is 3299 ± 11 Ma. In terms of geochemical characteristics, they correspond to TTGs. In the western part of the Bilotserkivka structure, we previously identified quartz diorites having an age of 3297 ± 22 Ma. These data show that the Bilotserkivka structure represents an ancient basement. Dislocated trondhjemites were studied in the Ivanivka area at the eastern part of the Saltycha anticline. They contain numerous relics of heavily altered amphibolites. The U-Pb age of zircons from trondhjemite is 3013 ± 15 Ma. These rocks are of the same age as TTGs of the Shevchenko Complex cutting through the sedimentary- volcanogenic rocks of the greenstone structures of the Azov Domain. They share age and geochemical characteristics with biotite and amphibole-biotite gneisses of the “Kainkulak beds” in the Zrazkove village located at the Mokra Konka river (3.1-3.0 Ga) and with biotite gneisses in the lower reaches of the Kainkulak river (2.92 Ga). Thus, gneisses of the “Kainkulak beds” actually represent the Mesoarchean TTGs of the Shevchenko Complex, transformed in the Paleoproterozoic time due to the dislocation metamorphism. The late Paleoarchean (3.3 Ga) tonalites are known in the West Azov and KMA domains; they probably also occur in the basement of the Middle Dnieper domains, where detrital zircons of this age have been reported. These data allow us to assume the existence of a large Late Paleoarchean (3.3 Ga) protocraton, in which the Mesoarchean (3.2-3.0 Ga) greenstone belts and TTGs of the eastern part of the Ukrainian Shield and the KMA Domain were formed.
<p>The Dizi Series is exposed within the Southern slope zone of the Greater Caucasus that occurs as a complex geological structure, which constitutes an integral part of the Mediterranean (Alpine-Himalayan) collisional orogenic belt. It is built up of terrigenous and volcanogenic-sedimentary rocks faunistically dated from the Devonian to Triassic inclusive (Somin, 1971; Somin, Belov, 1976; Kutelia 1983). Most of them are metamorphosed under conditions of chlorite-sericite subfacies of the greenschist facies of regional metamorphism (chlorite-phengite-albite&#177;quartz, graphite-sericite-quartz phyllites and marbleized limestones), and only a minor part represented by clay-carbonaceous, phengite-chlorite-carbonaceous and prehnite-chlorite-carbonate schists underwent anchimetamorphism (Shengelia et al., 2015). The Dizi Series is intruded by numerous magmatic bodies of gabbro-diabases, diabases, diorites, diorite-porphyries, syenites, monzo-syenites and granitoids. The age of the intrusions was defined by K-Ar method at 176-165 Ma (Dudauri, Togonidze, 1998) and by U-Pb LA-ICP-MS zircon dating at 166.5 &#177; 4.6 Ma (authors` unpublished data) and corresponds to the Bathonian orogeny. The Middle Jurassic intrusions caused intense contact metamorphism of the rocks of the Dizi Series resulted in the formation of various hornfelses containing andalusite, cordierite, corundum, biotite, plagioclase, potassium feldspar, clinozoisite, hornblende, cummingtonite, clinopyroxene, wollastonite and scapolite. These rocks correspond to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies of the contact metamorphism (Javakhishvili et al., 2020). The analogues of the Dizi Series rocks have not previously been established either in the Greater Caucasus or in the neighboring regions. In our view, Paleozoic rocks similar to the Dizi Series occur under the Cretaceous and Jurassic deposits within the folded basement of the plain Crimea where they were recovered by wells. Most of these rocks, as in the Dizi Series, underwent metamorphism of chlorite subfacies of the greenschist facies and, to a lesser extent, deep epigenesis (clayey-carbonaceous, sericite-carbonaceous, actinolite-chlorite-prehnite, muscovite-albite-chlorite, epidote-actinolite-chlorite and graphite-talc-quartz schists) (Chernyak, 1969). These rocks are also intruded by Middle Jurassic igneous rocks, including gabbro-diabases, diabases, diorites, syenites, monzo-syenites, granite-porphyries, etc. (Shniukova, 2016; Shumlyanskyy, 2019). As a result of the contact metamorphism of the basement rocks, muscovite-quartz-cordierite and cordierite-quartz-feldspar micaceous hornfelses were formed. Quartz syenite yielded a K-Ar age of 158 Ma (Scherbak, 1981), while monzo-syenite was dated at 170 &#177; 5 Ma applying 40Ar/39Ar method (Meijers, 2010). Thus, based on the rock associations, the nature of metamorphism, the age of the metamorphic and igneous rocks, and on the spatial position of the Dizi Series and folded basement of the plain Crimea we assume that these units developed coevally in similar environment and geological conditions.<br><br>Acknowledgements.This work was supported by Shota Rustaveli National Science Foundation (SRNSF) [PHDF-19-159, Regional and Contact Metamorphism of the Dizi Series].</p>
(1) Department of Geology, Lund University, Solvegatan 12, SE-22362 Lund, Sweden (Svetlana.Bogdanova@geol.lu.se), (2) Sodankyla Geophysical Observatory/Oulu Unit, University of Oulu, FIN-90014 Oulu, Finland, (3) Institute of Geophysics, Polish Academy of Sciences, Ks. Janusza 64, PL-01-452 Warsaw, Poland, (4) Institute of Geochemistry and Geophysics, Kuprievich 7, 220141 Minsk, Belarus,(5) Institute of Geochemistry, Mineralogy and Ore Fomation, NAS, Ukraine
The results of a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating and a Hf isotope study of zircon crystals separated from small eclogite xenoliths found in Devonian kimberlites within the Prypyat horst, Ukraine, have been reported. The studied area is located in the junction zone between the Sarmatian and Fennoscandian segments of the East European Platform. Four laser ablation sites on two zircon grains yielded Paleoproterozoic U–Pb ages between 1954 ± 24 and 1735 ± 54 Ma. In contrast, three of four Hf sites revealed negative εHf values and Paleoarchean to Mesoarchean model ages, excluding the possibility that the eclogite xenoliths represented segments of a juvenile Paleoproterozoic subducted slab or younger mafic melts crystallized in the subcontinental lithospheric mantle. A single laser ablation Hf spot yielded a positive εHf value (+3) and a Paleoproterozoic model age. Two models for eclogite origin can be proposed. The first foresees the extension of the Archean lower-crustal or lithospheric roots beneath the Sarmatia–Fennoscandia junction zone for over 200 km from the nearest known outcrop of Archean rocks in the Ukrainian Shield. The second model is that the Central Belarus Suture Zone represents a rifted-out fragment of the Kola–Karelian craton that was accreted to Sarmatia before the actual collision of these two segments of Baltica.
tHe bIlOKOrOVyCHI bAsIN, NOrtH-WesterN reGION OF tHe uKrAINIAN sHIelDThe Bilokorovychi basin is located in the North-Western region of the Ukrainian Shield.It is a 2 to 6 km wide and 22 km long weakly deformed and metamorphosed volcano-sedimentary basin that was formed between c. 1.98 and 1.80 Ga.The Palaeoproterozoic conglomerates and sandstones of the basin host unusual association of native gold and diamond.Native gold from conglomerates is variable in terms of its morphology and chemical composition.Massive fine anhedral gold grains prevail.Grains of the porous gold and grains with numerous autoepitaxic overgrowths of the secondary gold are also common.The microscale overgrown crystals are very variable in terms of their morphology and range from crystallographically undefined grains to ideal octahedrons and their intergrowths, including twins, fivelings, and skeletal octahedrons.chemical composition ranges from pure gold to medium-grade, silvery, and cuprous gold.Pure gold prevails.Gold and quartz intergrowths are common.Several types of native gold were distinguished according to the mineral assemblages and to the morphology and chemical composition of gold crystals.These types are detrital gold which is rather rare, and a prevailing authigenic gold including biogenic and secondary gold.Diamonds from conglomerates of the Bilokorovychi basin are the oldest so far found in europe.In terms of the crystal morphology, carbon isotope systematics, and the concentration and state of nitrogen admixture, Bilokorovychi diamonds resemble mantle-derived diamonds from kimberlites and lamproites.In terms of the degree of nitrogen aggregation, some of the Bilokorovychi diamonds are similar to the Archaean diamonds which crystallized in quiet conditions and a low thermal gradient in the mantle.Rest of the studied diamonds, according to the degree of nitrogen aggregation, had grown at higher temperatures which are more common for the Proterozoic diamonds.An average nitrogen concentration evidence that the studied diamonds are closer to the mantle eclogitic assemblage than to the peridotitic assemblage.The heavy roundness of diamond crystals indicates their prolonged transportation from the bedrock source to the site of deposition.The bedrock source may be represented by kimberlite, lamproite or other rock with the age exceeding or close to 1800 Ma.The most favorable model of the Bilokorovychi diamonds origin is a subduction model.Available data indicate that the North-Western region of the Ukrainian Shield was formed between c. 2150 and 1980 Ma due to continuous subduction of the oceanic lithosphere and gradual accretion of the newly-formed continental crust.A large-scale magmatic event that started at c. 1815 Ma could be a suitable transporter of the mantle-derived material, including diamonds, to the surface.
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