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Probability density curves for the analysed zircons and Concordia diagrams for samples from the Pass sub-zone of the Greater Caucasus.
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Here we report results of U-Pb zircon age data, obtained using LA-ICP-MS, from a total of 14 rocks of the Pass and Elbrus sub-zones of the Main Range Zone of the Greater Caucasus, which differ quite significantly from each other in composition of sedimentary and igneous rocks. Both exotic (detrital) zircons, and those formed within the Greater Cauc...
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... GE15 is a laminated orthogneiss from the Zgimazuk intrusive complex (Fig. 2). 32 grains (1 spot/grain) are analysed. Th/U = 0.04 to 0.87. The weighted mean age is 454 ±9 Ma (MSWD=2.2; Fig. ...
Similar publications
The Greater Caucasus fold-thrust belt is the northernmost expression of the Caucasus orogen and is accreted
to the southern margin of the Precambrian Scythian platform. This paper presents new data of zircon LA-ICP-MS
U-Pb geochronology of the Svaneti segment plutons of
this orogen. The data indicate three major stages of plutonic magmatic activity...
Citations
... The basement complex of the Greater Caucasus has a collage construction, which is thrust upon the Lower Jurassic formations along the Main Thrust of the Greater Caucasus (MTGC). In general, within the basement complex, four regional structuraltectonic zones are recognized from south to north: Southern Slope, Main Range, Fore Range and Bechasyn (Somin, 2011;Gamkrelidze et al., 2020). ...
... Numerous plutonic bodies of different ages, scales and genesis make this segment the perfect site for the investigation of orogenic plutonic magmatism. Although well-mapped, there are few isotopic or tectonic studies of the area (Okrostsvaridze and Clarke, 2004;Gamkrelidze et al., 2020). Svanetian plutonic magmatism has been broadly studied in terms of age groups (Paleozoic and Jurassic) (e.g., Borsuk., 1979;Okrostsvaridze, 1995;Gamkrelidze and Shengelia, 2005;Somin, 2011;Dudauri and Togonidze, 2016). ...
... The Main Range zone is the best exposed part of the basement complex and due to of the difference in structure, and composition it is divided into two sub-zones: the Pass and the Elbrus (Somin, 1971). They are in tectonic contact along the Alibak-Urukh regional fault, where the northern part of the zone is formed with the Elbrus sub-zone and the southern -Pass sub-zone (Gamkrelidze et al., 2020). The Elbrus subzone is mainly composed of felsic rocks, which have undergone low pressure-high temperature (LP-HT) metamorphism typical of subduction zones. ...
... The basement complex of the Greater Caucasus has a collage construction, which is thrust over on the Lower Jurassic formations along the Main Thrust of the Greater Caucasus. Within the basement complex, four regional structural-tectonic zones are recognized from south to north: Southern Slope, Main Range, Fore Range and Bechasyn (e.g., Gamkrelidze et al. 2020) Variscan plutons are localized in both the Pass and Elbrus subzones of the Main Range Zone. In the Pass Subzone, the plutons are mainly represented by I-type quartz-diorites and granodiorites, while the Elbrus Subzone -by Stype two-mica granites. ...
At the head of Enguri river (Georgia), along the Main Thrust of the Greater Caucasus, in the Shkhara crystalline massif, the high concentration uranium mineralization was discovered. The parent rocks of the mineralization are represented by biotite plagiogranites and migmatites. LA-ICP-MS 206 Pb/ 238 U dating of zircons from the plagiogranite vein indicates an age of 310.2±7.5. The Shkhara mineralization is represented by hydrothermally generated uraninite veins and nests. According to ICP-MS-ES analyses, in this rocks, the Th content varies from ~25 ppm to ~90 ppm, and the U varies between ~20 ppm to ~370 ppm. Geochemical studies of the uraninite veins on the JXA-8230 electron probe microanalyzer have shown that the U mineral is high-temperature Th-bearing uraninite that consists of uranium, thorium, lead and yttrium. The overall chemical U-Pb ages of the uraninite veins, to corresponds 291±14 Ma. According to the composition, geodynamic setting, tectonic localization, isotopic age and type of mineralization, the studied U mineralization is in full correlation with the same type of the Late Variscan Uranium Deposits of the Central and Western Europe. Therefore, we believe that investigation of the Shkara U mineralization is important both from a scientific and an economic point of view.
... Пери-Гондванский провенанс-сигнал надежно зафиксирован в палеозоидах Аппалачей (авалониды полуострова Авалон [Murphy et al., 2004]), Западной и Центральной Европы (авалонские и кадомские блоки -тектонические блоки Осса-Морена, Коимбра-Кордоба, Бежа-Акебучес и др. на Иберийском полуострове [Sánchez-García et al., 2003;Azor et al., 2021], Центрально-Французский, Саксо-Тюрингский, Богемский [Linnemann et al., 2007] и другие массивы); в киммеридах и альпидах [Zlatkin et al., 2014]), Анатолид-Таурид [Ustaömer et al., 2009;Zlatkin et al., 2013], Закавказья (Дзирульский массив [Mayringer et al., 2011]) и Большого Кавказа [Gamkrelidze et al., 2020;Somin, 2011;Vasey et al., 2020]). Недавно пояс пери-Гондванских террейнов был прослежен далее на восток до Южного Зауралья, где пери-Гондвандский провенанс-сигнал зафиксирован в некоторых геологических единицах палеозоид южной части Урала [Kuznetsov, Romanyuk, 2021]. ...
U-Th-Pb isotope dating of grains of detrital zircon from quartzites of the Suvanyak metamorphic complex, which forms the Suvanyak tectonic unit that forms the western part of the Uraltau uplift, located in the east of the West Ural megazone in the Southern Urals. The results of isotope dating of grains of detrital zircon from quartzites of the southern part of the Suvanyak metamorphic complex (samples G18-1 and R14-396) show that numerous populations of Late Neoproterozoic–Early Cambrian detrital zircon grains suggest a Peri-Gondwanan origin of the primary sources of detrital material for the protolith of the studied rocks.
The structure of the Suvanyak tectonic unit involves metamorphic formations of different ages – Early Paleozoic in the south and Late Precambrian in the north, which are now formally united into a single Suvanyak metamorphic complex. Their differentiation requires additional research.
For the Late Paleozoic southeastern margin of the Baltica (at that time already involved in the structure of the composite continent Arct-Laurussia), according to the results of isotope-geochronological study of detrital zircon from the sedimentary and metasedimentary sequences of the Southern Urals, a number of the following tectonic structures were identified. Near the southeastern edge of the margin, there was a Late Neoproterozoic–Early Cambrian oceanic basin, within which a volcanic arc or arcs were active during 650–520 Ma. The structure of the southeastern edge of the margin included the Peri-Gondwanan terrane or terranes (? Cadomian type), as well as thick Riphean-Early Paleozoic sedimentary sequences, autochthonous to the Baltica.
... Numerous plutonic bodies of different ages, scales and genesis make this segment the perfect site for the investigation of orogenic plutonic magmatism. Although well-mapped, there are few isotopic or tectonic studies of the area (Okrostsvaridze and Clarke, 2004;Gamkrelidze et al., 2020). Svanetian plutonic magmatism has been broadly studied in terms of age groups (Paleozoic and Jurassic) (e.g., Borsuk., 1979;Okrostsvaridze, 1995;Gamkrelidze and Shengelia, 2005;Somin, 2011;Dudauri and Togonidze, 2016). ...
... The Main Range zone is the best exposed part of the basement complex and due to of the difference in structure, and composition it is divided into two sub-zones: the Pass and the Elbrus (Somin, 1971). They are in tectonic contact along the Alibak-Urukh regional fault, where the northern part of the zone is formed with the Elbrus sub-zone and the southern -Pass sub-zone (Gamkrelidze et al., 2020). The Elbrus subzone is mainly composed of felsic rocks, which have undergone low pressure-high temperature (LP-HT) metamorphism typical of subduction zones. ...
The Greater Caucasus fold-thrust belt is the northernmost expression of the Caucasus orogen and is accreted
to the southern margin of the Precambrian Scythian platform. This paper presents new data of zircon LA-ICP-MS
U-Pb geochronology of the Svaneti segment plutons of
this orogen. The data indicate three major stages of plutonic magmatic activity that correspond to major orogenic
events in the region: 1- Ordovician (Caledonian orogenesis), 2-Late Carboniferous (Variscan orogenesis) and 3-
Middle Jurassic (Cimmerian orogenesis). In the Early
Ordovician (ca. 480 Ma), the granitoid protoliths crystallsized, wich later, during the Variscan orogeny, deformed
and metamorphosed (biotite orthogneisses). At the second stage, during Late Variscan orogenesis, Upper Carboniferous granodiorite-granite plutons (318–312 Ma)
were emplaced within Caledonian migmatised gneissic
infrastructure of the Pass and Elbrus subzones. At the
third stage, the Middle Jurassic monzo-syenite plutonic
activity is preserved in the Paleozoic-Triassic Dizi series.
The ages of the Middle Jurassic plutons gradually decreases
from north to south (177, 168, 164 Ma), which indicates
the time and direction of the Dizi basin closure. Combining of the spatial analysis with chronological constraints
provided by these plutons leads to the conclusion that the
northern margin of Neotethys subduction, were proceeding from south to north.
... The basement complex of the Greater Caucasus has a collage construction, which is thrust upon the Lower Jurassic formations along the Main Thrust of the Greater Caucasus (MTGC). In general, within the basement complex, four regional structuraltectonic zones are recognized from south to north: Southern Slope, Main Range, Fore Range and Bechasyn (Somin, 2011;Gamkrelidze et al., 2020). ...
The Greater Caucasus belt is the northernmost expression of the Caucasus orogen and is linked to the southern margin of the Precambrian Scythian Platform. In the pre-Jurassic crystalline basement of this belt, a plagiogranite vein, exposed in the headwaters of the Enguri River, with elevated radiation (μSv/h range of ~1-3), has been discovered. The vein is located along the Main Thrust of the Greater Caucasus, in the upper Paleozoic biotite migmatites of the Shkhara crystalline massif. It is ~2-3 m thick and represents hydrothermally altered rock (SiO 2 content varies from ~75% to ~85%) predominantly composed of a quartz-plagioclase assemblage. LA-ICP-MS 206 Pb/ 238 U dating of zircons from the vein indicates an age of 310.2±7.5 Ma that corresponds to the late Variscan orogenic activity. The vein is slightly fragmented and fractured, and fractures and nests are filled with Th-enriched uraninite veins and impregnations. According to ICP-MS-ES analyses, the Th content varies from ~26 ppm to ~50 ppm, and the U varies between ~55 ppm and ~290 ppm. Based on the conducted research, it was found that there is a full correlation between the studied vein and U-bearing granitic veins of different regions of the world by composition, magma series, geodynamic setting, tectonic location and isotopic age. On this basis, it is supposed that the late Variscan hydrothermally altered plagiogranite veins, which are localized in the shear zones of the Shkhara Massif, and entirely in the Main Range Zone of the Greater Caucasus, are potentially U-bearing.
... In the structure of the Greater Caucasus two major formations are distinguished: pre-Jurassic crystalline basement and Meso-Cenozoic magmatic and sedimentary formations. It has been interpreted that the pre-Jurassic basement in Paleozoic was an active continental margin, along which Paleo-Tethys oceanic crust was subducting to the north [15][16][17][18][19][20]. ...
... The basement complex along the Main Thrust of the Greater Caucasus (MTGC) is thrust over the lower Jurassic formations. In the construction of the basement complex four regional structural-tectonic zones are recognized from south to north: Southern Slope, Main Range, Fore Range and Bechasyn [20]. ...
... Because of differences in structure; and composition it is divided into two sub-zones: the Pass and the Elbrus. They are in tectonic contact along the Alibek-Urukh regional fault, where the northern part of the zone is built with the Elbrus sub-zone and in the southern part by -Pass sub-zone [20]. ...
A granite vein with a thickness of ~2-3 m exposed in the headwaters of the Enguri River, with elevated radiation (μSv/h fluctuates in the range of ~1-3) has been studied in detail. It is located along the Main Thrust of the Greater Caucasus, in the Upper Paleozoic biotite-bearing migmatites of the Shkhara massif. The vein represents hydrothermally altered rock composed of a biotite-quartz-plagioclase assemblage, whose zircon LA-ICP-206 Pb/ 238 U age was determined to be late Variscan (310.2±7). It is slightly fragmented and fractured, where the existing fractures and nests are filled with quartz and thorianite-uraninite veins. According to ICP-MS-ES multielement analysis, in this vein, the Th content varies from ~26 ppm ~50 ppm, the U-varies between ~55 ppm and ~290 ppm, while the content of all other chemical elements is within the normal concentrations. Of particular interest in this vein is an elevated concentration of uranium, as it is almost 100-200 times higher than normal. Those are industrial contents for the vein-type deposits. Based on the conducted research, it has been found that there is full correlation between the studied vein and of U-bearing granitic veins of different regions of the world, by genesis, composition, localization and age. Based on these data, we suppose that the Late Variscan hydrothermal plagiogranite veins, which are localized in the shear zones of the Shkhara massif granite-migmatite complex and entirely the Main Range Zone of the Greater Caucasus, may be potentially U-bearing. © 2021 Bull. Georg. Natl. Acad. Sci. Greater Caucasus, Shkhara massif, plagiogranite vein, U-Th mineralization As is known, thick felsic melts that are formed in subduction zones and experience postmagmatic hydrothermal action in the upper part of these structures is often enriched with economic deposites of metals [1-4]. These types of geodynamic regimes also form hydrothermal uranium-vein ore deposits, which make up ~ 30% of the global uranium reserves. Two main types of these uranium ore deposits are distinguished: granitic vein-like and breccia complex [5]. Breccia complex-type uranium ore deposits are mostly related to Proterozoic rocks (Ukraine, Australia,
... It should be noted that the ages of the crystalline basement of the Greater Caucasus and the Georgian Block bordering it from the south, which were determined employing the SHRIMP and LA-ICP-MS methods (Gerasimov et al. 2010;Somin 2011;Gamkrelidze et al. 2020), are similar to Zrn1 and Zrn2 populations. The age of crystallization of diorite-porphyrite (Zrn3, 166.5 ± 4.6 Ma) is fully consistent with the age of the Chegem orogeny. ...
The Dizi Series is exposed within the Southern Slope zone of the Greater Caucasus, in the core of the Svaneti anticlinorium. It is mainly composed of terrigenous, volcanogenic and carbonate rocks faunisti-cally dated from the Devonian to the Triassic inclusive. Regional and contact metamorphism of the Dizi Series rocks was studied. It is stated that the degree of regional metamorphism corresponds to the chlorite-sericite subfacies of the greenschist facies, occurring at a temperature of 300-350°C and a pressure of 1.5-2.3 kbar. As a result of the action of the Middle Jurassic intrusive rock bodies, the regionally metamorphosed rocks of the Dizi Series underwent contact metamorphism. Three zones of contact metamorphism were distinguished corresponding to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-bio-tite-muscovite-hornfels subfacies. Contact metamorphism took place at a significantly higher temperature and lower pressure than the preceding regional metamorphism. The maximum temperature of the contact meta-morphism reached ≈ 570°С, while pressure varied within the range of ≈ 0.3-0.8 kbar. The evolution of rock associations of regional and contact metamorphism of the Dizi Series was studied. The fields of facies and subfacies of regional and contact metamorphism are shown in the Ps-T diagram. Three age populations of zir-cons were identified using U-Pb LA-ICP-MS dating of the diorite-porphyrite intrusion in the Dizi Series: Zrn1 (ca. 2200 Ma) and Zrn2 (458 ± 29 Ma) that were captured by the diorite-porphyrite magma from the ancient magmatic and metamorphic rocks of the crystalline basement, and Zrn3 (166.5 ± 4.6 Ma) that corresponds to the age of diorite-porphyrite crystallization.
... 16. Сопоставление Hf-изотопных характеристик dZr из образцов K15-007 и K-15-003 Горного Крыма с аналогичными характеристиками для dZr из пород Украинского щита (по [116]) и комплекса Каракая (Западные Понтиды) (по [127] В распространенных в зоне Главного хребта герцинских метаморфических породах булгенского и лабинского комплексов (Перевальная подзона), а также гондарского и макерского комплексов (Эльбрусская подзона) установлены многочисленные унаследованные зерна циркона с возрастами в диапазоне от 500 до 675 млн лет [95,70]. ...
... Здесь мы коснемся лишь Большого Кавказа и его северного склона, сопряженного с Предкавказьем. Вполне исчерпывающие данные по геологическому строению Большого Кавказа, важные в контексте проводимого нами исследования, опубликованы в [9,22,70,95,119].В строении Большого Кавказа выделяются разделенные главным Кавказским разломом домены южного склона Кавказа и Северного Кавказа. Северокавказский домен состоит из расположенных с севера на юг более дробных единиц:-зона Главного хребта, включая Перевальную и Эльбрусскую подзоны;-зона Передового хребта. ...
В статье проведен синтез результатов выполненного U–Pb датирования зерен детритового циркона (dZr) из верхнедокембрийских–фанерозойских толщ южного и юго-восточного обрамления Восточно-Европейской платформы, верхнедокембрийских и кембрийских–ордовикских толщ Южного Урала, ордовикской толщи Прикаспия, а также юрских грубообломочных и верхнетриасовых флишевых толщ Горного Крыма. Проведен сравнительный анализ спектров U–Pb возрастов dZr из исследуемых толщ с аналогичными данными, характеризующими песчаники верхнедокембрийских и кембрийских–ордовикских толщ, участвующих в строении Пери-Гондванских террейнов. Показано, что пояс Пери-Гондванских террейнов, известный в северных Аппалачах, Западной и Центральной Европе, Ближнем Востоке, Северной Африке и Аравии, протягивается в северное Причерноморье, Предкавказье и Прикаспий, слагая фундамент Скифской и Туранской эпипалеозойских платформ, и прослеживается далее на восток, до южного Зауралья, принимая участие в строении палеозоид южной части Урала.
The mid-Tournaisian black radiolarian cherts of the Lydiennes Formation are exposed in deep-shelf successions of the Puech de la Suque and Col des Tribes sections of the Mont Peyroux Nappe area in the Montagne Noire, southern France. This interval represents the mid-Tournaisian anoxic event that is also termed the Lower Alum Shale Event. This event is associated with a global marine transgression that was characterized by increased productivity and drastic facies changes from pelagic carbonate sedimentation to the widespread deposition of black organic-rich siliceous shales and radiolarites in many parts of the world. In the present study, high-resolution inorganic geochemistry and framboidal pyrite analyses were employed to decipher changes in depositional conditions during the mid-Tournaisian anoxic event in the Montagne Noire. The results show that the total organic carbon contents of sediments associated with the Lower Alum Shale Event vary from 0.09 to 1.9 wt %. These low to moderate total organic carbon contents, high U/Th, low Corg/P and intermediate V/Cr ratios, enrichment in redox-sensitive trace elements, such as U, Mo and V, as well as varying sizes of pyrite framboids, indicate periodic dysoxic to anoxic bottom-water conditions during deposition of the studied sediments. Anomalous Hg spikes (>500 ppb) are also reported in the mid-Tournaisian deep-water marine succession of the Montagne Noire in the present study, which confirm a possible influence of increased regional volcanic activity during this environmental turnover.
