Precambrian Complex Research Articles

The Age, Composition, and Provenances of Terrigenous Rocks in the South of the Sangilen Block of the Central Asian Orogenic Belt

Abstract —We have first determined the petrogeochemical, Sm–Nd isotope, and U–Th–Pb geochronological (detrital-zircon LA-ICP-MS) characteristics of terrigenous rocks from a thick sequence in the south of the Sangilen block, which is part of the Central Asian Orogenic Belt (CAOB). The rocks are heterogeneous in facies composition: From west to east, there is a transition from graywacke sandstones with an admixture of pyroclastics to much more silicic lithoid arenites. Geochronological data on detrital zircons from the predominant graywacke sandstones mark the following intervals of concordant ages (Ma): 787–907, 1870–2236, 2613–2725, and 2900–2980. With regard to the oldest determined age (early Cambrian, 520 Ma) of the igneous rocks intruding these sandstones, the possible period of accumulation of terrigenous sequences in the south of the Sangilen block is estimated at 790–520 Ma. The obtained geochemical, Sm–Nd isotope, and U–Th–Pb geochronological data point to Neoproterozoic and early Precambrian island arc and continent-marginal complexes as probable provenances for the terrigenous deposits of the “southern band”. The relative proportions of rocks of these complexes in the deposits changed with distance from the sedimentary basin (from west to east, in modern coordinates): The portion of early Neoproterozoic juvenile rocks decreased, and the portion of early Precambrian metamorphic complexes increased. The Paleoproterozoic and Mezoarchean detrital zircons found in the terrigenous rocks of the Sangilen block could not originate from any known Precambrian complexes of the Tuva–Mongolian microcontinent. This gives grounds to regard other craton blocks of the CAOB as their sources.

Concerning the discussion about the Bug series of the Middle Bug (Ukrainian shield)

The materials of several articles and reports published in 2022 by the authors of this work and V.P. Kirilyuk (Kirilyuk, 2022 a,b), who discussed the structure and stratigraphy of the Вug area granulite complex of the Ukrainian Shield. The authors, relying on their geological, geophysical and geochemical studies, isotopic geochronology data, as well as on the world experience in studying the Early Precambrian complexes of the Canadian and Australian shields, argue that during 3.8—1.7 Ga, the Bug area granulite complex underwent at least a threefold structural metamorphic processing. Its modern structural plan, as well as, to a large extent, the composition and structural and textural features of metamorphic rocks, are of Early Proterozoic age. Therefore, its division into suites of primary sedimentary-volcanogenic rocks and their vertical distribution by age does not make sense. Only a division into two series is possible — the Dniester-Bug and the Bug, between which there is a tectonic contact. Contrary to this, V.P. Kirilyuk, relying on the experience of his stratigenic-metamorphogenic studies and the authority of the well-known school of L.I. Salopa, E.M. Lazko et al., defends the point of view on the stratigenic nature of the Bug area granulite complex, in which the primacy and stability of the position of strata-formations relative to each other were preserved throughout the entire time. According to V.P. Kirilyuk, there are no breaks and disagreements between the suites, so he proposes to abandon the identification of the early Precambrian USh Bug Group. And the seven suites identified by him, the youngest of which is 3.8 billion years old, are proposed to be attributed to a single Dniester-Bug series. The authors of both alternative points of view apply to the National Stratigraphic Committee of Ukraine with a proposal to revise the stratigraphic scheme of the Early Precambrian of the USh.

Structural Styles of Thrust Zones of the Urals and Pay-Khoi Foredeep

The article presents an interpretation of geophysical data characterizing the structure of the frontal fold and thrust zones of the Urals and Pay-Khoi, which show the diversity of structural styles of deformations in the study region. The following structural styles of deformations are considered: classical-style thrust zones, which are in-sequence thin-skinned imbrication systems (i); areas of distribution of wedge-shaped allochthons, composed of duplex tectonic plates that are not reflected in the sub-surface layers (ii); inversion zones where faults associated with Ural rifting are transformed into thrust faults (iii); areas whose structure is determined by the deformation of salt diapirs and extrusion of salt (iv); zone, tectonic thickening of the Precambrian complexes overlain by the Paleozoic cover (v). Interpretation of historical and new data on the structure of fold belts makes it possible to significantly update understanding of the structure and development of areas such as zones of wedge-shaped thrusts, areas of development of squeezed salt diapirs, and areas where reactivation and tectonic thickening of Precambrian complexes occurred due to the reactivation of pre-existing faults. New seismic data provided constraints on the magnitude of horizontal displacements in the thrust zones as well as timing of shortening. For the first time they have revealed the development of arrays of small-scale protothrusts.

Zealandia and Australia at Ordovician continental margins: reconciling their similar and differing detrital zircon provenances within Rodinia

ABSTRACT New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China.

Geochemistry of Xenoliths in Rapakivi Granites of the Korsun-Novomyrhorod Pluton (Ukrainian Shield)

Rapakivi of the Korsun-Novomyrhorod pluton (KNP), being the latest Precambrian granites of the central part of the Ukrainian shield, contain older acidic and intermediate rocks as xenoliths, the geochemical features of which reflect the Early Proterozoic geodynamic situation. Rapakivi granites, their differentiates and three types of xenoliths in them, represented by plagiogneiss, pink granite and charnockitoid (mangerite), were selected in the northwestern part of the KNP for geochemical studies. Analysis findings were compared with the geochemical characteristics of similar rocks of igneous and metamorphic Precambrian complexes that surround the KNP and could serve as a source of xenoliths. Based on distribution patterns of rare earth elements, lithophile elements content and their ratios relations in the rocks, taking into account their petrographic composition, it was established that plagiogneiss belongs to the upper part of the Inhul-Inhulets series, pink granite belongs to the Kirovohrad complex, and charnokitoid belongs to the intermediate rocks of the Tashlyk complex. In the latter, acid charnockitoids (enderbites) are probably younger than intermediate ones and were formed in another geodynamic setting. Pink granite, like the granites of the Kirovohrad complex, shows collisional geochemical features, in contrast to the rapakivi granites containing these xenoliths, which have predominantly within-plate geochemical characteristics. Thus, in the form of xenoliths in rapakivi those rocks were preserved that had been generated before and during the collision that occurred about 2 billion years ago and constructed a crust thickening at the site of the Inhul megablock, under subsequent extension of which about 1.75 billion years ago the KNP was intruded. Acid charnockitoids of the Tashlyk complex and rocks of the Novoukrainian complex, which are absent in xenoliths, probably were formed after the collision.

Late Mesozoic Adakite Granites in the Northern Framing of the Eastern Flank of the Mongol–Okhotsk Orogenic Belt

The examination of original and available petrochemical, geochemical, and isotope (Sm-Nd, Rb-Sr) data showed that subalkaline granitoids in the northern framing of the eastern flank of the Mongol–Okhotsk orogenic belt belong to the adakite series. The granitoids are characterized by high Sr/Y, Sr, Al2O3, and LREE, extremely low HREE concentrations, and the absence of negative Eu anomalies. The results obtained and the analysis of the geodynamic setting of their formation made it possible to assume that the granitoids were formed at a depth of more than 45 km through melting of garnet-bearing (20–50% garnet) rocks, which are likely represented by lower crustal Precambrian complexes widespread in the southern framing of the Siberian craton. The source of parental melts involved both mantle and crustal matter. This likely occurred in a subduction setting through melting of frontal or lateral parts of oceanic slab in subduction “windows”. The Late Jurassic–Early Cretaceous Chubachin adakite complex (149–138 Ma) was distinguished. Its formation preceded the initiation of suprasubduction differentiated calc-alkaline magmatism (140–122 Ma) in the northern framing of the eastern flank of the Mongol–Okhotsk orogenic belt.

Peculiarities of the present structure of the Bug granulite complex developed within the Middle Bug area and its partitioning into series and suits

The Gaivoron-Zavalie site and the Golovanevsk suture zone (GSZ) of the Bug mining region (BMR) in the Middle Bug region have been a «testing ground» for studying the structure and stratigraphy of the Early Precambrian complexes of the USh for many years. In the article, using their example, the Early Precambrian part of the Correlation Chronostratigraphic Scheme of the USh (CCS USh) and the issues arising around its discussion and the need for changes have been considered here. The main problem is to find out series, formations and rock strata in the CCS of USh, which is quite debatable. It has been shown that some rock strata (leucogranulite formation and Zelenolevadov rock strata, a significant part of the Koshar-Alexandrov suite) refer to the formation-genetic series of quartz-feldspar metasomatites, in particular, to the structural-formation association of metasomatites of zones of regional faults and they are not stratigenic. According to isotope-geochronological data, the bereznin rock strata is not Archean and therefore does not belong to the Dniester-Bug series. The layering, banding and gneissovity of the enderbite-gneiss complex of the Gaivoron-Zavalie section are associated with its intersection of a dense network of fault zones and therefore this area refers to the area of development of highly dispersed metamorphic tectonites, rather than the stratigene rock strata, which some researchers try to call the «Salkovska Formation». The association of the iron-ore strata of the Bug mining region into the Pavlov rock strata of the Archean Dniester-Bug series is not correct, because the present overlapped section of such rock strata has been studied in the Moldovian structure in the GSZ structure, and it refers to the Bug series. However, the genesis of iron-ore rocks is disputable, so the authors consider it undesirable to include them in the CCS of the Ukrainian shield. The genesis of graphitic gneisses and quartzites of the Khaschevato-Zavaliev suite is also disputable, which leads to the conclusion that it should be excluded from the CCS of the Ukrainian shield. With the exclusion of the Zelenolevadov, Bereznin, and Pavlov strata from the Dniester-Bug Series, only the strata of hyperstene and dipyroxene plagiogneisses and crystalline schists, called as Tyvrovka, remains in it. Its stratotype becomes the stratotype of the entire series, so the stratum “Tyvrov rock strata” can also be removed from the series. The authors conclude that the division of the Bug granulite complex into suites and rock strata is impractible. When considering the division of the Bug granulite complex into series, it is shown that the concept “series” as set forth in the Stratigraphic Code of Ukraine, although it does not take into account the features of formation of the Archean series, however does not contradict them. Therefore, separation of the Dniester-Bug and Bug series of different composition and age is quite natural. Contrary to the opinions of some researchers on the continuous process of accumulation of sedimentary-volcanogenic rocks of the Middle Bug area, it is shown that the anomalies in the age distribution of clastogenic zircons from the rocks of the Gaivoron-Zavalie and GSZ correspond to the global one and reflect a worldwide process of crustal formation, in which relatively quiet tectonic regimes alternated with periods of tectonic activation. During such periods, both magmatic and metasomatic processes and sedimentary-volcanogenic processes were activated. Materials of the study of the hafnium isotope composition from the zircons of the Dniester-Bug and Bug series rocks indicate a possible difference in the age of their formation of 600—700 Ma. The questions of the origin and rearrangement of the Bug granulite complex developed in the study area are also considered here.

What happened to the Early Precambrian granulite complexes of the Bug region (Ukrainian shield) and the Limpopo belt (South Africa) and how to stratify them? A tectonist’s view

The author reviews two alternative approaches (stratigenic-metamorphogenic and deformation-metamorphogenic) to the geology and mapping of the Earth’s oldest crust rocks that were metamorphized in РТ-conditions of the granulite facies, on the examples of two granulite belts — the Bug area complex (Ukrainian shield) and Limpopo belt (Southern Africa).
 There was shown a fairly good correlation of the composition and metamorphism (including the dynamometamorphism) of the rock complexes of both belts and their at least three-stage origin and transformation. The granulitic metamorphism processes within both belts happened before 3,0 b.y.a., 2,6—2,8, and c. 2,0 b.y.a. The structural-metamorphic transformations of the granulitic complexes, formation of their new structural plans with the destruction of the former (archean) by the following (proterozoan) do not allow falsifiably stratifying the archean granulitic complexes within the stratigenic-metamorphogenic approach already at the facies level. For the Bug area granulitic belt it is feasible only to isolate the Dniester-Bug and Bug series. Two of the important processes of the belt development are rock deformation in the compression and slip conditions and formation within the granulitic complexes of the sub-vertically-layered medium, slip folds with sub-vertical folds’ joints and wings. In both belts these processes began in the Neoarchean. This shows that in that time the tectonic processes were already to some significant degree propelled by plate tectonics mechanisms. Both belts had in common the formation of the linear-typeshearzonesat micro- to macroscale and their superimposition onto the deformation structures of the granulitic complexes of the preceding developmental stages. On their basis there formed the internal structure of the belts’ and their interconnections with the adjacent blocks of crust. Presumably, the archean charnokitoids and TTG-granitoids form the same structural layer of the crust, given their geochemical similarity and close age, and this layer is the base for the greenstone belts. The mineral composition, РТ-metamorphism conditions and age of granulitic belt rocks based on their U-Pb, Lu-Hf, Sm-Nd isotope systems compositions andoxygen isotope composition in Zirconium grains suggest that in the eo- and paleoarchean mantle and crust there should have already been amassed large quantities of medium-acidic matter which gave rise to the TTG complexes.

ГЕОЛОГИЧЕСКОЕ СТРОЕНИЕ ДОЮРСКОГО ОСНОВАНИЯ ЦЕНТРАЛЬНОЙ ЧАСТИ КРАСНОЛЕНИНСКОГО СВОДА В СВЕТЕ НОВЫХ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ДАННЫХ

The article reviews features of the pre-Jurassic geological structure of the Krasnoleninsky Swell, located on the western edge of the West Siberian petroleum basin. New geological and geophysical materials are presented enabling significant clarifification of the relationships pattern between Precambrian, Paleozoic and Triassic formation complexes. The stratification of the pre-Jurassic section is based on previously known age determinations and datings made in recent years by high-precision methods. The analysis of mode of occurrence of Pre-Jurassic rock complexes is based on the interpretation of seismic materials and gravity and magnetic data. The proposed model of the Krasnoleninsky Swell pre-Jurassic basement is characterized by the significantly reduced volume of pre-Cambrian formations due to the expansion of the Paleozoic complexes area, local Paleozoic depressions at the base of the Yem-Yegovskaya and Kamennaya peaks and linear zones of development of Triassic terrigenous-volcanogenic rocks on the Talinskaya Terrace and in the Palyanovsky trough have been identified. The conclusion is made about the long and complex history of the basement structure formation in the zone of collision junction of divergent Ural and Central-West Siberian folded systems.

A SUMMARY OVERVIEW OF DEPOSITS AND LARGE OCCURENCES OF NOBLE PRECAMBRIAN CORUNDUM IN THE WORLD

The paper is a summary review of the deposits and occurrences of noble corundum in Precambrian ore regions of the world. The ore bodies of ruby and sapphire deposits are divided into two groups. The first group comprises magmatic, pegmatite, and metasomatic deposits, mainly of Phanerozoic age. The second group is mainly represented by Precambrian formations. The article considers the formation of noble corundum associated with Precambrian complexes within the borders of provinces, belts and ore regions, and provides a brief description of corundum-bearing complexes in the Precambrian from Neoarchean to Neoproterozoic, with references to the respective deposits or occurrences. We indicate the P-T setup for metamorphism during the formation of corundum deposits from Precambrian corundum-bearing metamorphic complexes aged from 2.7–2.8 Ga to 610 Ma.

Paleogeography of the Late Precambrian basin in the south of the Siberian Platform

This work is largely a development of the ideas and continuation of the research of S. V. Bogdanova. For many years, she worked at the Department of Lithology of Gubkin University, engaged in research of Precambrian complexes, actively attracting young scientists. In her works, the main regularities of the spatial distribution of Precambrian complexes on ancient platforms were formulated.It is established that a system of folded structures existed on the western periphery of the Siberian Platform in the Late Precambrian already to the border 860 Ma. Some of them had a later age of 640 Ma. On the southern and eastern parts of the frame of the Siberian Platform in the Neoproterozoic, different-aged volcanic arcs that arose during the Neoproterozoic (the Late Riphean and Vendian) are reconstructed. Orogenic complexes from the west and southeast separated the platform sea basin from the Paleoasiatic Ocean and served as sediment provenance for the emerging foreland basin. The sediment provenance of sedimentary material for the Neoproterozoic terrigenous deposits of the sedimentary cover of the Siberian platform were located both inside the platform and on its periphery. The sediment provenances differed in the composition and age of the rocks composing them, and the glacial factor played a significant role in the transfer of sedimentary material. A fairly sharp differentiation of the composition of the sediment provenance rocks determined a wide variety of sedimentary material.Based on the results of U-Pb isotope dating of zircons, the age of the Taseeva Group in the south of the Siberian platform is determined, which cannot be older than 612 ± 6 million years. It is established that the formation of terrigenous deposits of Neoproterozoic productive complexes in the south of the Siberian Platform was significantly influenced by different age sources located both within the platform and on the territories surrounding it. They were composed of magmatic and metamorphic rocks with an age of 2800 up to 600 million years.

On the relationships between the Al2SiO5 polymorphs during formation of blastomylonites (North Yenisei Ridge)

Relevance. When mapping the vast areas of the Precambrian polymetamorphic complexes in the North Yenisei Ridge, there is a problem of metamorphism interpretation and phasing of geological development of a particular area along with thrust tectonics. The solution of these issues is also of great importance for the purposes of areas delineation of metamorphic rocks that are favorable for the detection of high-alumina (andalusite, kyanite, sillimanite) schists. Purpose of the work: to substantiate and itemize some geological prospecting, mineralogical and petrological indicator criteria for the development of high-alumina garnet-kyanite-staurolite blastomylonites of dislocation metamorphism formed by andalusite-bearing rocks of regional metamorphism. Research methodology: detailed mapping of structural-metamorphic zoning of dislocation (collisional) metamorphism in the Mayakon key area with sampling of polymetamorphic rocks for petrographic studies of mineral parageneses. Investigation of polished thin sections of polymetamorphic rocks by microprobe analysis with elucidation of minerals zoning, their chemical composition, calculation of the Р–Т paths of metamorphism and determination of the absolute age of blastomylonite formation based on the 40Ar/39Ar dating of biotite. Analysis and generalization of the results obtained for the Mayakon area and their comparison with other key areas of the North Yenisei Ridge. Results. At the Mayakon potential area, a progressive metamorphic zoning of kyanite-bearing blastomylonites has been identified, and the transitional I, outer II, middle III, and inner zones are determined as the dislocation metamorphism intensifies towards the Panimba thrust fault. Based on the compositions of garnets, biotite, and plagioclase, the P–T paths of the early regional metamorphism of andalusite-sillimanite type and late local kyanitesillimanite type were calculated. A list of geological prospecting, petrological and isotope-geochronological criteria for recognizing blastomylonites among rocks of regional metamorphism in thrust zones has been substantiated and itemized. Conclusions. Method of polymetamorphism reconstruction in the North Yenisei Ridge shows that tectonic inversion conditions took place in the Neoproterozoic, in the late Tonian era (~850 Ma ago In terms of occurrences, they are related to the final stage of the Grenville orogeny (1.1–0.85 Ga). The formation of blastomylonites of dislocation (collisional) metamorphism by metapelites of regional metamorphism in thrust zones is accompanied by an increase in the number of mineral phases and leads to a reduction in usable space of high-alumina andalusite schists.

Formation of the Neoproterozoic Continental Crust in the Structures of the Central Segment of the Central Asian Fold Belt

The paper considers the results of geochronological (U-Pb method, ID-TIMS), geochemical, and Sm-Nd isotopic studies of granitoids, volcanics, and terrigenous rocks of the eastern Dzabkhan terrane, as well as felsic volcanics of the Dzabkhan Formation in its southern part. It is established that the post-kinematic granitoids of the Dzabhan–Mandal Zone, Erdenekhairkhan, and Bogdoingol blocks were formed in the range of 813 ± 9–772 ± 3 and ca. 720 Ma, and the rhyolites of the Dzabkhan Formation were formed at 790 ± 3 Ma. The rock sources in the southern part of the terrane and in the Bogdoingol Block were mainly ancient crustal complexes. Nd isotopic data on the rocks of the Dzabkhan–Mandal Zone and the Erdenekhairkhan Block demonstrate the mixed nature of their sources and suggest a significant contribution of Early Neoproterozoic juvenile material. Based on obtained and previous data, it is shown that the Dzabkhan terrane is not a homogeneous block of the Early Precambrian continental crust, but represents a Neoproterozoic composite terrane consisting of rocks of island arc and continental margin complexes, and reworked Early Precambrian continental crust. The correlation of the Precambrian complexes of the Dzabkhan terrane with those of the Songino, Baidarik, and Tarbagatai terranes is discussed, and features of the formation of the Neoproterozoic continental crust in the central segment of the Central Asian fold belt are considered. It is established that the Khangay group terranes comprise widespread oceanic, island arc, continental margin, and riftogenic complexes formed at ca. 960–930, 880–850, and 810–790 Ma. Based on the data obtained, a model of the formation and evolution of the Neoproterozoic crust of the Central Asian fold belt is proposed by the example of paleoreconstructions for 925 and 825 Ma. It is assumed that the extensive growth of the Neoproterozoic continental crust of the region was related to the subduction processes in the framing of the Rodinia supercontinent at about 960–860 Ma ago and continental rifting that initiated the breakup of the supercontinent in the middle Tonian at about 860 and 800 Ma ago.

Фосфаты Стрельцовского рудного поля Юго-Восточного Забайкалья (Часть 3)

The conclusions’ reliability of geologists who created the largest uranium ore base in the country on the territory of the Streltsovsky ore field (SOF) in the South-Eastern Transbaikalia, about the belonging of spatially isolated phosphate mineralization and powerful industrial mineralization to a final stage of Late Mesozoic tectonomagmatitic activation, is clarified. The relevance of the research lies in the need to study the geological materials at the SOF and the surrounding area to assess the prospects for involving in the exploitation of phosphate mineralization developed on the flanks of uranium deposits developed under the state program of the TOP. The object of study is the “blind” Argunskoye and Zherlovoye deposits and their western flanks on the surface, and the subject is the phosphate mineralization developed in the block of terrigenous-carbonate rocks. The purpose of the research is to clarify the time and features of the formation of phosphates, and the task is to assess the industrial significance of phosphate mineralization for decision-making. The methodology of scientific research is based on the interpretation of geological facts given in the literature and stock materials, use of concepts, terms, creation of hypotheses and their consequences, consistency of the comparison of which with the established facts determines the relatively high reliability of geological results. The author has used a descriptive method that takes into account a system of interrelated consistent positions, and a method of theoretical modeling, which raises the strategic goals of nature cognition to a higher scientific level. The results of the research are presented in three articles (parts). In the second part, phosphates of the region and SOF are characterized. It is established that the Talan manifestation of apatites belongs to the phosphate sorption-biogenic metalliferous formation of the Precambrian metamorphic rocks complex and combines the promising second and third most important industrial types of deposits. It is recommended to perform geological exploration at the evaluation stage and to test the electrothermal method for producing fused phosphate-magnesium fertilizers. In the third part, the known types of phosphogenesis and the genetic features of their manifestation in PSA are considered. Attention is drawn to the advantage of the recommended electrothermal method for processing apatite-carbonate and apatite-silicate rocks of the Talan manifestation

Age and Composition of Zircons From the Devonian Petrivske Kimberlite Pipe of the Azov Domain, the Ukrainian Shield

Results of a study of U-Pb and Hf isotope systematics and trace element concentrations in five zircon crystals separated from the Devonian Petrivske kimberlite are reported in the paper. Four zircons have yielded Paleoproterozoic and Archean ages, while one zircon grain gave a Devonian age of 383.6±4.4 Ma (weighted mean 206Pb/238U age). The Precambrian zircons have been derived from terrigenous rocks of the Mykolaivka Suite that is cut by kimberlite, or directly from the Precambrian rock complexes that constitute continental crust in the East Azov. The Devonian zircon crystal has the U-Pb age that corresponds to the age of kimberlite emplacement. It is 14 m.y. younger than zircon megacrysts found in the Novolaspa kimberlite pipe in the same area. In addition, Petrivske zircon is richer in trace elements than its counterparts from the Novolaspa pipe. Petrivske and Novolaspa zircons crystallized from two different proto-kimberlite melts, whereas the process of kimberlite formation was very complex and possibly included several episodes of formation of proto-kimberlite melts, separated by extended (over 10 M.y.) periods of time.

Возраст монацита из метапелитовых сланцев серий Атомфьелла и Моссель (полуостров Ню-Фрисланд, о. Западный Шпицберген) по данным Th-U-Pb (CHIME)-датирования

The article presents the results of CHIME (chemical Th–U-total Pb isochron method) dating of monazite from metamorphic rocks of Precambrian complexes located in the north part of the West Spitsbergen Island. It is shown that for rocks of Atomfjella Series and Mossel Series, monazite ages are coeval within error (Atomfjella Series: 381 ± 18 Ma, Mossel Series: 377 ± 23 Ma). These age estimates show that metamorphism of the crystalline basement possibly took place during the Late Caledonian orogeny.

Geospatial mapping and suitability classification of groundwater quality for agriculture and domestic uses in a Precambrian basement complex

Application of groundwater for domestic and agricultural uses has increased in sub-Sahara Africa. However, geology and anthropogenic activities can impact groundwater quality. But information on quality evaluation and suitability classification of groundwater based on water quality index (WQI) is limited. Thus, this study evaluated the spatial variability of groundwater quality and its suitability for potable and irrigation purposes in a Precambrian complex of southwest Nigeria. Water samples were collected from 40 wells across the study area and analyzed for physicochemical properties. Suitability for domestic and irrigation uses were determined. Maps showing spatial variations of pH, electrical conductivity (EC), total dissolved solid (TDS), total hardness (TH), cations (Ca2+, Mg2+, Na+, and K+), anions (SO42−, Cl−, NO3−-N, PO3−-P, B−, F−, and HCO3−) and irrigation water quality index (IWQI) and drinking water quality index (DWQI)) were produced using ArcGIS. The average values of pH, EC, TDS and TH were 6.6, 0.3 dS m−1, 152.4 mg L−1, and 208.7 mg L−1, respectively. The concentrations of Ca2+, Mg2+, K+ and Na+ were 28.7, 32.8, 2.49, and 7.13 mg L−1, respectively, whereas SO42−, Cl−, NO3−-N, PO3−-P, B−, F−, and HCO3− concentrations were 20.4, 0.32, 0.46, 0.04, 0.39, 0.42, and 230.7 mg L−1, respectively. The quality indices for irrigation (IWQI) and drinking (DWQI) were 0.22 and 0.75, respectively. The IWQI significantly correlated with Mg2+, TH, SO42−, pH and TDS (P ≤ 0.05, r = 0.34–0.66), whilst DWQI significantly correlated with TDS, SO42−, Cl−, NO3−-N, PO3−-P, Ca2+, Mg2+, pH, TH, and F− (P ≤ 0.05, r = 0.38–0.93). The suitability classification of the groundwater quality in the area shows that 100% and 78% of the water are safe for irrigation and domestic purposes, respectively. However, regular quality monitoring of the groundwater is recommended in order to avert likely deterioration indicated by some quality parameters.

Late Precambrian Metamorphic Complexes of the Ulutau Massif (Central Kazakhstan): Age, Composition, and Formation Settings of Protoliths

This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been traditionally identified with the most ancient Early Precambrian complexes, comprising the massif’s basement. The protoliths of the metamorphic rocks, represented by lavas and tuffs of basalt and rhyolite–trachyrhyolite composition, sandstones, and tuffaceous sandstones, comprise a contrasted volcanic-sedimentary sequence. The obtained U‒Th–Pb zircon ages (LA–ICP MS, SHRIMP II) demonstrate that the formation of this sequence occurred during a narrow (762–788 Ma) interval during the second half of Tonian (Neoproterozoic). The metamorphic transformations of the rocks were completed before an intrusion of the alkaline syenites of the Karsakpai complex (673 ± 2 Ma), which were not subject to metamorphism. The whole-rock Nd isotopic compositions of the metamorphic rocks indicate the origin of their protoliths due to erosion and partial melting of the more ancient complexes of the Precambrian continental crust of the Ulutau massif. The Hf isotopic compositions of zircons indicate that the main stages of formation and transformation of the Ulutau continental crust occurred during the Neoarchean–Neoproterozoic and coincided with the main stages of the Precambrian magmatism in the western part of the Central Asian Orogenic Belt.

New approaches to the study of the material composition and geodynamic evolution of the early Precambrian complexes

Geological interpretation of formation processes of Precambrian assemblages with a complicated structure (reconstruction of geodynamic formation settings of metamorphic rocks protoliths) requires approaches other than those applied in studying Phanerozoic objects. The current paper reports some new approaches to studying the material composition and geodynamic evolution of early Precambrian complexes. They are based on the authors’ techniques of identifying the original nature of metamorphites, statistic modeling of varied features of chemical compositions of Precambrian objects in regard to standards of geodynamic settings in the Phanerozoic and considering them in geodynamic reconstructions.

Isotope Characteristics of Carbonates from Rocks of Greenstone Belts as an Indicator of a Possible Source of Fluids in Precambrian Granulite Complexes: An Example from the Giyani Greenstone Belt and the Limpopo Granulite Complex, South Africa

Data on the carbon and oxygen isotopic composition of carbonates from the rocks of the Giyani greenstone belt, Kaapvaal craton, South Africa are presented. This belt is immediately adjacent to the Hout River Shear Zone, along which the Southern Marginal Zone (SMZ) of the Limpopo granulite complex is overthrusted onto the Kaapvaal craton. The δ13C values are –2.1 and –2.2‰ for carbonates from two metapelite samples, –5.1‰ for a meta ultrabasite sample, and –7.1 and –7.7‰ for two metabasite samples, respectively. The δ18О values are 17.1 and 17.5‰ for carbonates from the metapelites, 14.3‰ for carbonates from the metaultrabasite, and 12.9 and 13.0‰ for carbonates from the metabasites. The comparison of the data obtained to the published data on the isotopic composition of carbonates from the rocks of the different greenstone belts indicates both hydrothermal (in the metabasites and the metaultrabasite) and sedimentary (in the metapelites) origins of the carbonate material in the rocks studied. Based on the comparison of these data to δ13C of magnesite that formed in ultrabasic granulites during the interaction of the Limpopo complex with the craton, the graphite and fluid inclusions in leucocratic garnet-bearing granitoids that transported fluids, and the carbon isotopic composition of graphite from metapelites of the SMZ, it is concluded that the carbon source was located outside the SMZ and represented a heterogeneous carbonate-bearing lithologies. It could be carbonate-bearing volcanogenic–sedimentary sequences of the greenstone belts of the Kaapvaal craton, which underwent prograde metamorphism during the interaction with the SMZ granulites.