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Abstract Geochronological, geochemical, and structural studies of magmatic and metamorphic complexes within the Kyrgyz North Tianshan (NTS) revealed an extensive area of early Palaeozoic magmatism with an age range of 540–475 Ma. During the first episode at 540–510 Ma, magmatism likely occurred in an intraplate setting within the NTS microcontinent and in an oceanic arc setting within the Kyrgyz-Terskey zone in the south. During the second episode at 500–475 Ma, the entire NTS represented an arc system. These two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature, which led to obduction of ophiolites from the Kyrgyz-Terskey zone onto the microcontinent. The occurrence of zircon xenocrysts and predominantly negative whole-rock ɛ Nd(t) values and ɛ Hf(t) values of magmatic zircons suggest a continental setting and melting of Precambrian continental sources with minor contributions of Palaeozoic juvenile melts in the generation of the magmatic rocks. The late Cambrian to Early Ordovician 500–475 Ma arc evolved mainly on Mesoproterozoic continental crust in the north and partly on oceanic crust in the south. Arc magmatism was accompanied by spreading in a back-arc basin in the south, where supra-subduction ophiolitic gabbros yielded ages of 496 to 479 Ma. The relative position of the arc and active back-arc basin implies that the subduction zone was located north of the arc, dipping to the south. Variably intense metamorphism and deformation in the NTS reflect an Early Ordovician orogenic event at 480–475 Ma, resulting from closure of the Djalair-Naiman ophiolite trough and collision of the Djel'tau microcontinent with the northern margin of NTS. Comparison of geological patterns and episodes of arc magmatism in the NTS and Chinese Central Tianshan indicate that these crustal units constituted a single early Palaeozoic arc and were separated from the Tarim Craton by an oceanic basin since the Neoproterozoic. Graphical abstract Unlabelled Image Highlights • Extensive Cambrian to Early Ordovician magmatic realm revealed in the Kyrgyz North Tianshan • A magmatic arc evolved on heterogeneous basement, mainly on Precambrian continental crust. • Arc-related rocks represent crustal melts with minor contribution from juvenile sources. • The Kyrgyz North Tianshan and Chinese Central Tianshan represent a single early Palaeozoic arc. [ABSTRACT FROM AUTHOR]

U-Pb geochronological studies have shown at least two stages of Neoproterozoic magmatism, 940-933 and 804-789 Ma, throughout the geologic evolution of the Bureya continental massif in the east of the Central Asian Fold Belt. The first stage (940-933 Ma) was marked by the formation of the protoliths of metagabbroids and amphibole-biotite gneiss-granites of the Bureya River basin. The geochemical features of these rocks suggest that they formed, most probably, in an island-arc setting on the continental basement or on an active continental margin. The second stage (804-789 Ma) of magmatism was manifested as the formation of biotite leucogranites and hastingsite-lepidomelane granites (A-type granites) in the Chepkan River basin. The latter rocks are similar in geochemical features to within-plate granitoids. The established stages of magmatism are the most ancient for the continental massifs in the east of the Central Asian Fold Belt. It is not ruled out that these magmatism stages were related to the stages of formation and breakup of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

The performed 40 Ar/ 39 Ar geochronological studies yielded the first reliable age of trachyandesites of the Mogot volcanic field (115 ± 3 Ma), which, together with the age of trachyandesites of the Bomnak volcanic field (117 ± 1 Ma), gives grounds to recognize a new stage (117–115 Ma) of evolution of the Stanovoi volcanoplutonic belt superposed on the igneous and metamorphic complexes of the Dzhugdzhur–Stanovoi superterrane of the Central Asian Orogenic Belt and Stanovoi structural suture. The trachyandesites of the Mogot volcanic field are similar in geochemical features to adakites. Their parental melts resulted from the transformation of Precambrian continental crust under postcollisional extension after the formation of the Mongolo–Okhotsk orogen or under sliding along the boundary between the North Asian craton and the Amurian microcontinent. [ABSTRACT FROM AUTHOR]

There are four main types of boninites in ophiolite suites, which either spatially coexist with ophiolites though belong to other tectonic units (1), or are present as later constituents of ophiolite sequences (crosscutting dikes or lavas on top) (2), or build ophiolite sequences together with island-arc tholeiites and basaltic andesites, followed by younger volcanics of MORB or BABB affinites (3), or occupy the whole mafic portion of ophiolite sequences, together with island-arc tholeiites and basaltic andesites (4). The latter type, considered in more detail for the case of ophiolites from the southeastern Sayan Mountains (Siberia, Russia), presents an example of inconsistency between the model of ophiolite formation in mid-ocean ridge settings and subduction-related island-arc fingerprints in ophiolitic mafic rocks. The patterns of boninites record several evolution models of oceanic systems, with melting and intrusion of boninites in forearc, arc, and back-arc settings. The existing models are controversial, possibly, because there is no single mechanism to account for all types of boninites. [ABSTRACT FROM AUTHOR]

The Ider Complex of the Tarbagatai Block in northwestern Mongolia is part of a Precambrian microcontinental terrane in the Central Asian Orogen Belt and has experienced a polymetamorphic tectono-metamorphic evolution. We have investigated an enderbitic gneiss, derived from a quartz diorite and a charnockite, derived from a leucogranite, and zircon SHRIMP data reveal late Archaean protolith ages of 2520–2546 Ma for these rocks. Metamorphic overgrowth on these zircons as well as newly-formed metamorphic zircons document a high-temperature metamorphic event (T = 930–950 °C) at about 1855–1860 Ma. Nd whole-rock isotopic systematics show these and other gneisses of the Ider Complex straddling the CHUR-line in a Nd isotope evolution diagram, suggesting both crustal reworking and input of some juvenile material, with Nd model ages ranging between ca. 2.5 and 3.1 Ga. Hf-in-zircon isotopic data provide a similar pattern and also yielded Archaean Hf crustal model ages. The metamorphic zircons seem to have inherited their Hf isotopic composition from the igneous grains, suggesting a complex process of dissolution, transportation, and re-precipitation involving a fluid phase during high-grade metamorphism. The zircon age patterns do not make it possible to unambiguously assign the Tarbagatai Block to any of the cratons bordering the Central Asian Orogenic Belt, since age peaks at ca. 2520–2550 and ca. 1860 Ma are common in the Siberian, North China and Tarim cratons. [ABSTRACT FROM AUTHOR]

Abstract: We present new data on the geologic position, composition, and isotope characteristics of the Early Cretaceous granitoids of the Samarka terrane, Sikhote-Alin’, formed on a transform continental margin. Geological and geochronological data show that these granitoids were generated at two stages of magmatism: in the first half (Hauterivian–Barremian, 130–123 Ma) and second half (Albian–Cenomanian, 110–98 Ma) of the Early Cretaceous. Granitoids of the first stage form an autonomous (free of basic precursors) unimodal melanogranite–granite association and are characterized by normal alkalinity with domination of K over Na, low contents of Ca, and elevated contents of Al2O3. By composition, these are S-granites with a model Nd age of ∼1.3 Ga. Granitoids of the second stage are of more diverse petrogeochemical types. They show wider variations in K/Na and A/CNK, are richer in Ca and, sometimes, Sr, and are poorer in P than the granitoids of the first stage. Their compositions form a continuous trend from S- to I-granites, and their model Nd age is ≤1.2 Ga. Comparison of the petrochemical, trace-element, and isotope characteristics of the Early Cretaceous granitoids and upper-crustal rocks (sandstones and siltstones of the turbidite matrix of a Jurassic accretionary prism and basalts from the inclusions in it) of the Samarka terrane and the coeval garrboids has shown that the potassic S-granitoids formed at the early (Hauterivian–Barremian) stage of magmatism as a result of the anatexis of upper-crustal sedimentary rocks. At the late (Albian–Early Cenomanian) stage, the intrusion of mantle magmas led to a temperature increase in the lower crust, which favored more active anatexis, involvement of high-melting substrates (oceanic basalts) in the granite formation, and interaction of mantle and crustal magmas. This resulted in a great diversity of granitoids (from S- to I-type). [Copyright &y& Elsevier]

Abstract: We generalize results of geological, geochronological, geochemical, and isotope-geochemical studies of the Vendian–Early Cambrian island-arc plagiogranitoid magmatism in the Altai–Sayan folded area and in the Lake Zone of western Mongolia. Based on these data, we analyzed the scales of development of plagiogranitoid magmatism, studied the petrologic composition and isotope characteristics of granitoids, and established the main sources of plagiogranitoid-generating melts and the leading mechanisms of formation of Early Caledonian juvenile crust. [Copyright &y& Elsevier]

Abstract: The structure, composition, and age of Vendian–Early Cambrian plagiogranitoid associations composing the Kshta and Taraskyr massifs of the Yenisei pluton in the Altai–North Sayan island-arc belt are considered. We have established that these associations formed within 550–520 Ma and differ in petrographic composition and sources. Two stages of island-arc plagiogranitoid magmatism are recognized: early (550–540 Ma, formation of plagiogranitoids of the Kshta (545 ± 8 Ma) and Taraskyr (545 ± 7 Ma) massifs) and late (525–520 Ma, formation of plagiogranitoids of the Maina complex of the Yenisei (524 ± 2 Ma) and Tabat plutons). By petrochemical composition and geochemical characteristics, the rocks of the Kshta massif are high-alumina plagiogranitoids similar to adakites. They might have been produced through the melting of metabasites compositionally similar to N-MORB in equilibrium with garnet-containing restite during the subduction of oceanic slab at ≥15 kbar. The rocks of the Taraskyr massif are low-alumina plagiogranites. They formed through the melting of metabasites located in the lower layers and(or) the basement of the island-arc system in equilibrium with plagioclase-containing restite at 3–8 kbar. The low-alumina plagiogranitoids of the Yenisei pluton melted out under the same conditions. Isotope-geochemical studies showed that the Vendian–Early Cambrian plagiogranitoids formed at the early stage are characterized by high positive ∑Nd(T) values (7.5–4.9), Late Riphean model Nd-age (TNd(DM) = 0.64–0.98 Ga), and Sr isotope ratio varying from 0.7040 to 0.7053. These data point to the juvenile parental melts of the rocks and the varying content of ancient crustal material in the magma generation zone. [Copyright &y& Elsevier]

Abstract: In the Tannu-Ola zone, there are island-arc (Late Vendian) and subduction-accretionary (first half of the Early Cambrian) complexes whose mantle sources were generated from melts produced in suprasubduction conditions as a result of the melting of mantle wedge peridotites. The island arc, whose fragment is present in the Tannu-Ola zone, formed tentatively at 570 Ma and ceased as an individual structure at the Vendian–Cambrian boundary, though the subduction continued till the middle Early Cambrian. From the Vendian–Cambrian boundary to middle Early Cambrian, the accretion of island-arc, back-arc, oceanic, and metamorphic structure-lithologic complexes took place at this segment of the Central Asian Fold Belt. From middle to late Early Cambrian, the Tannu-Ola zone was an active continental margin, where basalts with island-arc characteristics, quartz microdiorites of adakite composition, basalts, dolerites, and quartz microdiorites of intraplate type, and diorite-tonalite-plagiogranite association of island-arc type formed. To explain the spatial and temporal conjugation of different magmatism manifestations on the active margin, we applied the slab–window model. [Copyright &y& Elsevier]

Abstract: The history of the Vendian–Early Paleozoic formation of protoliths of continental crust in the Gorny Altai segment of the Central Asian fold belt is considered, and their composition, isotopic characteristics, and formation mechanisms are estimated. We have established two stages of crust-forming processes in Gorny Altai: Early and Late Caledonian, with the different structures of formed geoblocks and nature and compositions of crustal protoliths. At the Early Caledonian stage, fragments of oceanic lithosphere of basic composition (MORB, OIT, OIB) (T Nd(DM-2st) = 0.65–1.1 Ga) formed, as well as island arcs with andesite-basaltic and andesitic protoliths with low contents of incompatible elements (T Nd(DM-2st) = 0.7–0.9 Ga). At the Late Caledonian stage, the redistribution of the substance of these blocks and the external supply of material led to the formation of heterogeneous crust of turbidite basins with an oceanic basement and andesite-dacitic upper-crustal protoliths (T Nd(DM-2st) varies from 0.8–0.9 Ga in the framing of the volcanic arc of Altaids to 1.4–1.6 Ga at the boundary of the Altai–Mongolian microcontinent). [Copyright &y& Elsevier]

Abstract: We discuss problems of the origin, settings, and age of Neoproterozoic A-type leucogranites widespread in the Yenisei Ridge. Combined analysis of geological, petrological, and geochemical (including isotope) data shows that some granitoids (Glushikha complex) were formed at the postcollisional stage (750–720 Ma), and others (Tatarka complex), in an anorogenic environment (680–630 Ma). The anorogenic complex contains diverse igneous rocks, including alkaline varieties and carbonatites. Leucogranites form separate plutons within different igneous complexes. They have high contents of potassium (up to ultrapotassic composition in the Glushikha complex), iron, and fluorine and are depleted in europium. Postcollisional granitoids show the highest concentrations of Rb, Th, and U, extremely low concentrations of Ba and Sr, whereas anorogenic granitoids are rich in Ta, Nb, Y, Sm, and HREE. The obtained data point to the augmented mantle contribution to the formation of continental crust of the Yenisei Ridge between 750 and 630 Ma. We also report new results of U-Pb zircon dating, including SHRIMP and Ar-Ar data. [Copyright &y& Elsevier]

Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and whole-rock Nd isotopic compositions for granitoid gneisses of the Kuilyu Complex elucidate the age, origin and tectonic settings of this oldest continental fragment in the Tianshan. The Kuilyu Complex is part of the basement in the Ishim - Middle Tianshan microcontinent. It consist of a strongly deformed and metamorphosed supracrustal assemblage of paragneisses and schists which are tectonically interlayered with amphibolites, migmatites and granitoid gneisses. Our zircon dating indicates that the Kuilyu Complex contains two suites of Palaeoproterozoic granitoid gneisses with magmatic protolith ages of ca. 2.32–2.33 Ga and 1.85 Ga. Granitoid magmatism at 1.85 Ga was almost immediately followed by amphibolite-facies metamorphism at ca 1.83 Ga, evidenced by growth of metamorphic zircon rims. The older, ca 2.3 Ga granitoid gneisses chemically correspond to calc-alkaline, metaluminous, I-type magnesian quartz diorite and granodiorite. The protolith of the younger, ca. 1.85 Ga granite-gneiss is an alkalic-calcic, metaluminous to peraluminous, ferroan medium-grained porphyric granite with chemical features resembling A-type granites. The 2.3 Ga and 1.85 Ga granitoid gneisses have slightly to distinctly negative initial ε Nd values of −1.2 and −6.6, and similar depleted mantle Nd model ages of 2.7–2.6 Ga, which imply melting of Neoarchaean continental crust. The zircon age patterns of the Kuilyu Complex resemble those of exposed rocks in the Tarim Craton, where episodes of granitoid magmatism at ca. 2.3–2.4 and 1.85 Ga, followed by amphibolite-facies metamorphism at ca 1.85 Ga, are also recorded. Similarities in the early Precambrian magmatic and metamorphic episodes as well as similar histories during the Neoproterozoic and early Palaeozoic suggest that the Ishim-Middle Tianshan microcontinent was rifted off the Tarim Craton. Similar age patterns also suggest possible tectonic links of the Kuilyu and Tarim continental blocks with the Baidrag Block of central Mongolia. In contrast, substantial differences in age and Precambrian evolution between the Anrakhai block of southern Kazakhstan and the Kuilyu Complex argue against a previous connection and suggest the former to represent an independent continental terrane. Current data show that early Precambrian rocks in the western CAOB outside Tarim only occur at two sites, namely in the Anrakhai Complex of southern Kazakhstan and in the Kuilyu Complex of eastern Kyrgyzstan. [ABSTRACT FROM AUTHOR]

This paper presents new geochemical, U–Pb geochronological, and Sm–Nd isotopic data for early Paleozoic granitoids and acidic volcanic rocks within the Mamyn Terrane that constrain the early Paleozoic tectonic evolution of the eastern central Asian orogenic belt (CAOB). The Mamyn Terrane is usually considered part of the Argun Massif, although our new geochronological data indicate the presence of two magmatic events within the terrane that occurred at the Ediacaran–Cambrian boundary (∼541 Ma) and the late Cambrian–Early Ordovician boundary (507–488 Ma). Field observations indicate that all of the late Ediacaran–Early Cambrian (∼541 Ma) volcanic rocks are deformed whereas the Late Cambrian–Early Ordovician (507–488 Ma) intrusive and volcanic rocks are either deformed or undeformed. The ∼541 Ma magmatic event in the study area produced rhyodacite, trachyrhyodacite, and trachyrhyolite units that are either high-K calc-alkaline or shoshonitic. These units have ε Nd(t) values from −7.4 to −8.7, t Nd(DM) ages of 1.9–1.8 Ga, and formed from primary magmas generated by the partial melting of Mesoproterozoic continental crustal material in a suprasubduction zone setting. The Late Cambrian–Early Ordovician (507–488 Ma) magmatic event in this area formed gabbrodiorite, diorite, granodiorite, granite, trachyrhyodacite, and rhyodacite units that are medium-K and calc-alkaline, and have arc-like trace element compositions that are enriched in the large ion lithophile elements (LILEs) and depleted in the high field strength elements (HFSEs). These units have initial 87 Sr/ 86 Sr (i) ratios and ε Nd(t) values that range from 0.7048 to 0.7067 and from −3.3 to −0.2, respectively, yielding t Nd(DM) ages of 1.6–1.1 Ga. These features indicate that the magmas that formed these units were generated in a subduction zone setting, most likely by the partial melting of Mesoproterozoic crustal material with the addition of some younger juvenile material. In addition, the Late Cambrian–Early Ordovician trachyrhyodacite and rhyodacite units in this area are high-K and calc-alkaline or are shoshonitic and are enriched in K, Rb, the rare earth elements (REE), Y, Nb, Ta, and Zr, and are depleted in Sr and have A-type granite affinities. However, these units do not contain alkali amphibole or pyroxene and have high FeO tot /MgO ratios (6.7–12.7) that indicate they formed from highly fractionated magmas. Therefore, these volcanic rocks represent extreme melt differentiates that also formed the coeval granites. The early Paleozoic magmatic events within the Mamyn Terrane have also been identified in the Argun, Bureya, and Jiamusi areas of the eastern CAOB, suggesting that all of these areas have a common geodynamic history. [ABSTRACT FROM AUTHOR]

The geological, structural and tectonic evolutions of the Yenisey Ridge fold-and-thrust belt are discussed in the context of the western margin of the Siberian craton during the Neoproterozoic. Previous work in the Yenisey Ridge had led to the interpretation that the fold belt is composed of high-grade metamorphic and igneous rocks comprising an Archean and Paleoproterozoic basement with an unconformably overlying Mesoproterozoic–Neoproterozoic cover, which was mainly metamorphosed under greenschist-facies conditions. Based on the existing data and new geological and zircon U–Pb data, we recognize several terranes of different age and composition that were assembled during Neoproterozoic collisional–accretional processes on the western margin of the Siberian craton. We suggest that there were three main Neoproterozoic tectonic events involved in the formation of the Yenisey Ridge fold-and-thrust belt at 880–860 Ma, 760–720 Ma and 700–630 Ma. On the basis of new geochronological and petrological data, we propose that the Yeruda and Teya granites (880–860 Ma) were formed as a result of the first event, which could have occurred in the Central Angara terrane before it collided with Siberia. We also propose that the Cherimba, Ayakhta, Garevka and Glushikha granites (760–720 Ma) were formed as a result of this collision. The third event (700–630 Ma) is fixed by the age of island-arc and ophiolite complexes and their obduction onto the Siberian craton margin. We conclude by discussing correlation of these complexes with those in other belts on the margin of the Siberian craton. [Copyright &y& Elsevier]