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The paper discusses possible immiscibility between fluoride salt ("cryolite") and silicate liquids into which the parental melt of the Katugin massif exsolves, and the petrological implications of this phenomenon. Results of a detailed study of the cryolite and zircon are presented. Liquid immiscibility is demonstrated to have triggered the massive crystallization of zircon and, together with the processes of subsequent evolution of the cryolite melt, contributed to the formation of the large cryolite bodies. Data on mineral-hosted inclusions were used to estimate the crystallization temperatures of fluoride salt and silicate melts and outline the pathways of their evolution during the formation of the massif. It is shown that the granites of the Katugin and West Katugin massifs were most likely derived from distinct sources, that differed mainly in fluorine content. Data on the chemical composition of three zircon generations identified in the granites of the Katugin massif are presented. [ABSTRACT FROM AUTHOR]

Geochemical, geochronological (U–Pb zircons, ID-TIMS) and isotope-geochemical (Sm–Nd) studies of the rocks of the Bambukoy volcano-plutonic association, which form the Zhanok-Bambukoy volcano-tectonic structure within the Anamakit–Muya terrane on the northern flank of the Barguzin–Vitim superterrane of the East Transbaikalian segment of the Central Asian orogenic belt. The association includes volcanic rocks of the Zhanok Suite (dacites and rhyolites mainly), as well as leucocratic and biotite granites of the Bambukoy Complex that cut through them. The granites of this complex host the Mokhovoe tin deposit, which is attributed to the tin-porphyry formation. Subvolcanic rocks of the Zhanok Suite are considered as ore-bearing. The geochemical features of the volcanic rocks of the Zhanok Suite and the granites of the Bambukoy complex bring them closer to S-type granites, and belonging to a single tin-bearing Bambukoy volcanic-plutonic association. The formation of this association is determined by the age interval 834 ± 23–818 ± 7 Ma. The isotopic data point to a source of parental magmas from the rocks of the Bambukoy volcano-plutonic association, formed as a result of mixing of the material of two crustal sources, the mature Early Precambrian and the juvenile Early Baikal. The geochemical data also point to an exclusively crustal source of the rocks of this association. Thus, the Bambukoy tin-bearing volcano-plutonic association was formed in the Neoproterozoic time (Tonian), most likely under lithospheric extension conditions due to a source with a complex and long crustal prehistory. [ABSTRACT FROM AUTHOR]

The temporal relations between alkaline rocks of the Aryskan rare metal (Y, REEs, Nb, Ta) deposit are determined using metamict zircon with high U and Th contents, which was prepared for geochronological U–Pb (ID TIMS) studies following a special procedure. Dating of this zircon from alkali granites of the Aryskan and neighboring Astyg plutons showed that they formed synchronously: 448 ± 1 and 446 ± 1 Ma, respectively. The suggested genetic link of alkali granites with country alkali feldspar syenites formed at 472 ± 2 Ma (zircon, U–Pb, ID TIMS) is not confirmed. [ABSTRACT FROM AUTHOR]

The higher alkali granitoids traditionally combined into the Middle Paleozoic (Silurian–Devonian) Ognit complex are widespread in the Oka part of the Eastern Sayan region. The Snezhnoe biotite–phenakite–beryl deposit is located within their outcrops. Its age was earlier determined at 305 Ma. The geochronological U–Pb (ID-TIMS) studies of zircon from alkali granites containing the deposit resulted in an age of 311 ± 1 Ma. A similar age (307 ± 1 Ma) was obtained for monzogabbro from the bimodal gabbro–alkali granite assemblage in the Ust'-Sentsa massif in the same area. The obtained age estimates are indicative of the fact that, along with Ognit Middle Paleozoic granitoids, Late Paleozoic alkali granitoids and moderately alkali gabbro assemblages were also formed within the Oka part of the Eastern Sayan region. Their characteristic feature was enrichment in rare metals and the structural connection with the Eastern Sayan riftogenic rare-metal magmatism zone. [ABSTRACT FROM AUTHOR]

The possibility of the application of high-uranium self-irradiation-damaged metamict zircon for U-Pb geochronological studies (ID-TIMS) after preliminary high-temperature annealing and acid treatment was demonstrated using zircon from the Li–F granites of the Turga massif (Eastern Transbaikalia). Optimal conditions of high-temperature annealing and acid treatment of zircon with high self-irradiation α-dose can be selected to remove completely a metamict phase and preserve sufficient quantities of the mineral for U-Pb (ID-TIMS) studies. [ABSTRACT FROM AUTHOR]

The paper reports geochemical, geochronological (ID–TIMS zircon U–Pb) and isotope–geochemical (Nd, Pb) study of granitoids of the Kodar complex developed in the western part of the Aldan shield. It has been established that these rocks can be classified as postcollisional A–type rapakivi granites, which together with the mafic–ultramafic rocks of the Chinei complex compose a single magmatic association formed within 1876 ± 4–1859 ± 2 Ma. The massifs of this association are a part of the giant South Siberian magmatic belt over 2500 km in length, which was formed at the final stage (1.88–1.84 Ga) of evolution of the Paleoproterozoic orogen. Globally, this belt is the largest stitching suture, which marks the formation of the Siberian craton and its entrance into the Paleoproterozoic Nuna supercontinent. The formation of the initial magmas of the Kodar granitoids was related to the mantle–crustal interaction during the mixing of primary mafic mantle magmas or their derivatives with anatectic melts derived through partial melting of the Archean lower continental crust of the region under the thermal influence of mafic magma. The crustal component in the source clearly predominates and has a heterogeneous nature. The mantle component is mainly represented by ancient enriched mantle, with the possible contribution of the OIB–type component. [ABSTRACT FROM AUTHOR]

The principal possibility of using high-uranium metamict zircon with a high self-irradiation α-dose for U–Pb geochronological studies (ID-TIMS) is demonstrated. The application of the optimal parameters of "chemical abrasion," accompanied by preliminary high-temperature annealing, allowed us to estimate the age of Li–F granites of the Turga massif (Eastern Transbaikalia) (146 ± 4 Ma and 141 ± 1 Ma). [ABSTRACT FROM AUTHOR]

Granite–porphyries of the Yazovka complex occur in the northern part of the Riphean Baikal–Patom fold-thrust belt within the Tonod Uplift of the Early Precambrian basement. The geochronological (U–Pb), isotope-geochemical (Sm–Nd), and geochemical studies have shown that the rocks of this complex belong to A-type tin-bearing granites of the age of 709 ± 7 Ma. Initial magma of these granites was formed from the mixed Early Precambrian crustal and mantle source in the intraplate geodynamic setting. This tectonic event was global in nature and manifested the Late Riphean impulse of the lithospheric extension, which was associated with breakup of the supercontinent Rodinia under the influence of a mantle superplume. [ABSTRACT FROM AUTHOR]

Abstract: The Elikanskiy granite-gneiss swell represents a structure, similar to Late Mesozoic Cordilleran-type metamorphic core complexes allocated within the Eravninskiy terrane of the Yenisei-Transbaikal tectonic collage, the Mongolo-Okhotskiy orogenic belt and a northern part of the Argun-Idermeg superterrane of the Central Asian orogenic belt. The main elements of a geological structure of the Elikanskiy metamorphic core complex are the detachment zone, core and upper nappe. The detachment zone separating a core from the upper nappe is represented by a thick zone of blastomylonites and a zone of chlorite breccias. That zone was formed under the conditions of tangential stress and led to the exhumation and structural and metamorphic transformations of magmatic rocks of the Bukhtochinskiy Complex and metamorphic rocks of the Upper Olekma Complex, which compose the core of the considered structure. The upper nappe consists of Jurassic and Cretaceous stratified rocks of the Kyker-Akimin and Usuglinskiy basin and the Early Paleozoic-Mesozoic volcanoplutonic complexes in its southeastern framing. The Elikanskiy metamorphic core complex is a part of a huge belt of metamorphic core complexes which is traced along the northern border of the Mongolo-Okhotskiy orogenic belt on distance about 2000 km. The formation of the Elikanskiy metamorphic core complex as well as other similar complexes in the eastern part of the Central Asian orogenic belt is connected with collapse of the Late Mesozoic orogen which has resulted from the accretionary and collision events connected with closing of the Mongolo-Okhotskiy paleoocean basin and respectively formation of the Mongolo-Okhotskiy orogenic belt. [ABSTRACT FROM AUTHOR]

The Dotulur alkalic granite and Usugli Depression volcanics (West Stanovoi Superterrane of the Central Asia Fold Belt) have been dated by the U-Pb method, and their geochemistry has been analyzed. The geochemistry of the rocks suggests their intraplate nature. The alkalic granite and volcanics have similar ages of 142 ± 1 Ma and 138 ± 3 Ma, respectively. Considering the Usugli Depression structural position as an upper fault slice of the Elikan metamorphic core, the obtained dates allow the formation of the mentioned core and, accordingly, the collapse of central part of the Mongol-Okhotsk orogeny to have occurred not prior to 140 Ma. [ABSTRACT FROM AUTHOR]

This work presents the results of U-Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite-granodiorite (Zerenda and Krykkuduk), Early Silurian granite-leucogranite (Borovoe and Karabulak), Late Silurian granosyenites-granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes. [ABSTRACT FROM AUTHOR]

U-Pb dating of the Torangalyk Complex (Northern Balkhash) yielded a Late Carboniferous age of 305 ± 2 Ma. Taking into account the previous data, a new scheme for Late Paleozoic granitic magmatism in this region has been proposed. It includes the Early Carboniferous granite-granodiorite Balkhash Complex, Late Carboniferous monzonite-granosyenite Kokdombak and Torangalyk complexes, and the Late Carboniferous-Early Permian granite-leucogranite Akchatau Complex. [ABSTRACT FROM AUTHOR]

Geological, mineralogical, petrographic, geochemical, and geochronological data are reported for granitoids of the Aturkol Massif (Gorny Altai). It is shown that it was formed in within-plate setting in the Early Triassic, nearly simultaneously with flood basalts of the Kuznetsk Basin and alkalic basite and lampropyre dike swarms in the western Altai-Sayan Fold Region. At the same time, the mineralogical-petrographic, geochemical, and isotope characteristics of the considered granitoids are close to those of I-type granites. Intraplate signatures (elevated HFSE and REE) are recognized only in the least silicic rocks (granosyenites). Obtained data suggest mantle-crustal nature of the granitoids. They were formed by mixing of lamprophyre magmas with high pressure (>10 kbar) crustal melts derived from a mixed source consisting mainly of N-MORB-type metabasites with insignificant admixture of high-Ti basalts and metasedimentary rocks. The contribution of mantle component in the granitoids was insignificant (<20%). Proposed petrogenetic mechanism can provide the formation of large volumes of granitoid magmas with 'crustal' geochemical and isotope signatures in an intraplate setting. [ABSTRACT FROM AUTHOR]

The crystallization age of Zhaunkar granites (829 ± 10 Ma) was determined by U-Pb zircon dating. Taking into account the data obtained earlier on the granite age (791 ± 7 Ma) in the Aktas Complex and the syenite age (673 ± 2 Ma) in the Karsakpai Complex, the Ulutau sialic massif is assumed to be composed of three igneous complexes formed during the Tonian-Cryogenian periods of the Neoproterozoic. [ABSTRACT FROM AUTHOR]

This paper reports on geochronological U–Pb studies of baddeleyite from nepheline syenite of the Korgere-Daba alkaline massif, which is the largest massif within the Sangilen Highlands (Tyva). The established age of rocks, 295 ± 1 Ma, indicates that, in the Early Permian, undersaturation by silica magmatism occurred in the region in addition to the alkaline-granite magmatism (Ulug-Tanzek, etc.). This age furthermore points to the need to make corrections in the conceptions of a petrophysical type for the Devonian Sangilen complex, which is traditionally distinguished in this region. Until now, the Korgere-Daba massif has been considered in this regard. [ABSTRACT FROM AUTHOR]

Structural studies showed that the Elikanskii granite-gneiss swell is similar to the Late Mesozoic Cordilleran-type metamorphic core complexes distinguished in the southern part of the Eravninskii terrane and in the northeastern part of the Argun-Idermeg superterrane of this belt. [ABSTRACT FROM AUTHOR]

The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U-Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural-geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm-Nd isotopic-geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan. [ABSTRACT FROM AUTHOR]

Isotope-Geochemical Sm-Nd studies of the Early Proterozoic alkaline granites of the Katugan complex (Aldan shield) were carried out. The unique Katugan rare metals (Ta, Nb, Zr, Y, and REE) deposit is confined to these granites. Parent melts of the granites are of mantle-crustal nature. [ABSTRACT FROM AUTHOR]

Granitoid massifs of the Olekma Complex form a large synonymous magmatic belt, which is located in the southern part of the Selenga-Stanovoi superterrane and is traceable in the northeasterly direction for over 700 km. According to U-Pb geochronological data, they are 358 ± 2 Ma old. The geochemical data indicate their collisional nature. The massifs were most likely formed during collision between the Selenga-Stanovoi superterrane and structures of the Baikal mountainous system and its terminal formation stage as a single structural block. [ABSTRACT FROM AUTHOR]

An Early Carboniferous (352-359 Ma) U-Pb (TIMS, SIMS) age is established for granitic rocks of the Kibera pluton, quartz sienites of the Kuekvun pluton, and granites from the pebbles in the basement of Carboniferous rocks of the Kuul and Kuekvun uplifts in the Central Chukotka region. These data support the suggestion of granitic magmatism to occur in the region in the Late Paleozoic. The petrogeochemistry of most granitic rocks of the Kibera and Kuekvun plutons is similar to that of I-type granites, and their age coincides with tectonic events of Ellesmerian Orogeny in the Arctic region at the Late Devonian-Early Carboniferous boundary. The Devonian-Early Carboniferous granitic complexes extend to the territories of the Arctic Alaska, Yukon, and Arctic Canada, which indicates a common geological evolution within the Chukotka-Arctic Alaska block, which experienced a motion away from Arctic Canada. [ABSTRACT FROM AUTHOR]

The article presents study to determine age of ore-bearing granitoids of the Konyrat Porphyry Copper deposit in the North Balkhash Region, Central Kazakhstan. It mentions that Tokrau Batholith is composed of tonalite, granodiorite and plagiogranite. It adds that lower part of the volcanic-sedimentary complex of the deposit comprises of sandstones with lenses of crinoidal limestone.

It was established that amphibolites of the Kichera zone of the Baikal-Muya belt (BMB) belong, at least, to two age groups: (I) Early Neoproterozoic large metamafic xenoliths entrapped by granitic rocks of 750 Ma and (II) Late Neoproterozoic (650-620 Ma) amphibolites, which compose individual tectonic sheets and lenses. The rocks of these groups are distinct in chemical composition: the low-Ti amphibolites of the first group with increased AlO contents are similar to modern IABs, whereas the highly-Ti amphibolites of the second group correspond to MORBs and OIBs. The geochemical data showed that the igneous protoliths of amphibolites of the Kichera zone were formed during different stages of the BMB evolution distinct in geodynamic settings. [ABSTRACT FROM AUTHOR]

Rhyolite-granite volcanoplutonic association was identified among the Precambrian basement complexes of the Aktau-Mointy Massif, Central Kazakhstan. This association comprises rhyodacites, rhyolites, subalkaline rhyolites, tuffs, and felsic volcanogenic-sedimentary rocks of the Altyn Syngan and Urkendeu formations, as well as granitoids of the Uzunzhal Complex. U-Pb (ID-TIMS) dating of accessory zircons from the volcanic rocks and granites showed that the association was formed in the Neoproterozoic (Tonian, 925-917 Ma). The Neoproterozoic volcanic rocks and granites are the youngest Precambrian magmatic complexes and mark the final stage in the formation of the Precambrian crust of the Aktau-Mointy Massif. In terms of major and trace element composition, the volcanic rocks and granites resemble A-type granites, thus indicating the within-plate settings of their formation. It was established that their primary magma could be derived by melting of metatonalitic or metagraywacke protolith at T ≥ 940°C and P ∼ 8-10 kbar in response to mantle magma underplating. Sm-Nd isotope data on the volcanic rocks and granites (T(DM) = 1.9−1.7 Ma, ɛ(T) from −1.9 to −3.5) testify the Paleoproterozoic age of their crustal protolith. Available data have revealed strong similarity between the Neoproterozoic tectonomagmatic evolution of the Aktau-Mointy Massif and the Congo-São Francisco paleocontinent, which, with other cratons, composed the southern Rodinia supercontinent. This suggests that the formation of the Tonian anorogenic volcanoplutonic association of the Aktau-Mointy sialic massif was related to the global-scale divergent processes in the southern Rodinia supercontinent (Congo-São Francisco paleocontinent). [ABSTRACT FROM AUTHOR]

Data obtained on the Khangai zonal magmatic areole in the Central Asian Orogenic Belt indicate that accessory zircons in alkaline granitoids have crystallogenetic characteristics that generally reflect specifics of the evolution of the parental alkaline magmas. The late differentiation of these magmas was characterized by an increase in the concentrations of trace and rare-earth elements, water, and fluorine in the residual melts and aqueous salt-bearing fluids. Their action was associated with local transformations of the zircon, first and foremost, with local enrichment of zircon crystals in fluid inclusions and in crystalline inclusions of sulfides an other ore minerals. This disturbed the Pb isotopic composition of the zircon, for example, led to its enrichment in common (admixture) Pb and thus caused significant errors and uncertainties in the U-Pb zircon dates. Our recently obtained data indicate that one of the most efficient methods of preparing accessory zircons enriched in common Pb to their U-Pb dating is their preparatory treatment with acids (Makeev, 1981; Mattinson, 1994, 1997, 2005). The application of this technique makes it possible to rid the zircons of phases enriched in common Pb and usually to obtain reliable geochronologic data. The method of preparatory acid treatment of zircons is thus best suitable for geochronologic studies of granitoids of elevated alkalinity. [ABSTRACT FROM AUTHOR]

The article discusses the geodynamic evolution of granitoids of Tukuringra Complex in the Selenga-Stanovoi Superterrane of the Central Asian mobile belt. Topics discussed include the uranium-lead geochronological investigations of diorites the first phase and granites of the second phase of the Tukuringra Complex, Tukuringra Complex that are alkaline rocks belonging to the calc-alkaline and crystallization of zircons from magmatic melt.

The article discusses geochemical and geochronological data of granitoids, granitic rocks, from Tynda–Bakaran Complex in Uda–Zeya magmatic belt, Russia. It mentions that these granites are mixture of basite and felsic magmas, and their age determined with the help of host rocks. It also mentions techniques used for geochronological data including isotopic analyses, and use of zircon grains and heavy liquids.

The article focuses on the structure and age of the Baikal granitoid Massif and new evidence for early Baikalian events in the Baikal-Muya Mobile Belt which is a well-studied tectonotypes of the Late Proterozoic fold belts of Central Asia. Topics discussed include geological aspects of the development of this belt, isotopic–geochemical (Sm–Nd) investigations of granitoids from the Baikal massif, and gneissic granites ranging from low-alkaline varieties to leucogranites.

The article discusses the geochronological study of the trachyrhyolites of the Ulkan Group. It states that the volcanic deposits overlie metamorphic rocks of the Early Proterozoic era. It mentions that Riphean deposit sequence is considered as Siberian hypostratotype. It adds that isochronous Rb-Sr method was used to identify the age of the crust located at the base of Lower Riphean Uyan Group. Furthermore, the chemical composition of volcanites correspond to igneous rocks while associated granites and acid volcanites correspond to granites which are A-type.

The article offers information on a study on the Chelkar Peridotite-Gabbronorite Pluton in Kazakhstan. It informs that Chelkar pluton is composed of peridotites, gabbro, and norites which is intruded by large bodies of Late Ordovician granites. It was found in the study that the Chelkar pluton having a complex layered intrusive body was formed in the late Middle-early Late Ordovician and cannot be a part of the ophiolitic section. It informs that it was marked by the intense magmatic activity of the Stepnyak-North Tien Shan ensialic island arc having the Kokchetav massif in its back part.

The U-Pb geochronological study of zircons from alkali granitoids of the Elenovsk Complex constituting the Zhilanda and Lesnoi massifs (northern Kazakhstan) located several kilometers away from each other revealed their close ages: 433 ± 2, 440 ± 10, and 426 ± 12 Ma. [ABSTRACT FROM AUTHOR]

The basement of the south Ulutau sialitic massif, which is located in the western part of Central Kazakhstan, comprises metamorphized volcanogenic-sedimentary and plutonic complexes of Proterozoic age. The upper boundary of the metamorphism age corresponds to the age of nonmetamorphized syenites from the Karsakpai massif (673 ± 2 Ma, Late Riphean). U-Pb geochronological studies of accessory zircon were made, and a Late Riphean age of biotite alkali granite from the Aktas massif (the youngst metamorphic Precambrian igneous units in South Ulutau) was found. The obtained age estimate of 791 ± 7 Ma can be considered as the lower age limit of metamorphism. Thus, the last stage of regional metamorphism in South Ulutau took place in the second half of the Late Riphean, in the time interval of 790-670 Ma. [ABSTRACT FROM AUTHOR]

Geological and isotopic study of rocks occurring in the Early and Late Baikalian, Caledonian, Hercynian, and Indosinian fold regions of Central Asia is carried out. The juvenile crust formation occurred in these fold regions have determined the systematic differences in isotopic compositions of the crust. In the course of the subsequent (postaccretion) evolution, the crust of these domains underwent multiple reworking. These processes were accompanied by variations in the Nd isotopic compositions of the crust, which, in turn, are recorded in the isotopic compositions of granites and felsic volcanics as products of crust melting. Three types of crust differing in Nd isotopic composition and structure and, as a consequence, in formation mechanisms, are distinguished. The isotopically homogeneous crust is a source of igneous rocks with constant model Nd isotopic age (T(DM2st)) irrespective of the age of the crustal igneous rocks. These are the isotopic provinces, the crust of which remained isolated from addition of alien materials during postaccretion evolution. The axial zone of the Hercynides in the Central Asian Foldbelt is an example. The isotopically heterogeneous layered crust consists of fragments differing in isotopic composition. The products of its melting are characterized by widely scattered ɛ(T) and (T(DM2st). The appearance of alien sources of melt is considered in terms of underplating. This mechanism develops either due to subduction of the juvenile oceanic lithosphere beneath the mature continental lithosphere at convergent boundaries or as a result of plume-lithosphere interaction. The first mechanism operated during the formation of granitoids pertaining to the Tuva-Mongolia microcontinent. The second mechanism was responsible for the formation of batholiths in the zonal Hangay, Barguzin, and Mongolia-Transbaikalia magmatic fields. The isotopically heterogeneous mixed crust is composed of fragments differing in isotopic composition, which are tectonically mixed, resulting in the formation of an isotopically uniform reservoir in the domain of magma generation. As a result, the products of melting acquire isotopic parameters substantially distinct from the juvenile rocks of the corresponding structural zone. The formation of such a crust is related to the tectonic delamination, which provides for juxtaposition and a high degree of tectonic mingling of heterogeneous fragments at deep levels. The Caledonides of the Central Asian Foldbelt are characterized by such a mechanism of crust formation. [ABSTRACT FROM AUTHOR]

Systematized geological, geochronologic, geochemical, and Sm-Nd isotopic geochemical data obtained over the past decade on A-granitoids in the Aldan Shield and in adjacent mobile belts surrounding it in the south make it possible to identify the sources from which the rocks were derived and the geodynamic environments in which they were generated. The territory in question provides evidence of five episodes of Early Precambrian within-plate magmatism, including the derivation of A-granites: at 2.62, 2.40-2.52, 2.07, 1.87-1.88, and 1.70-1.74 Ga. Although all of the granitoids were derived within plates, the environments of their derivation were different: (i) postcollisional lithospheric extension at 2.64 and 1.87-1.88 Ga in an anorogenic environment and (ii) in relation to the activity of mantle plumes at 2.40-2.52, 2.07, 1.74-1.70 Ga. The postcollisional magmatism generated only potassic granitoids of the subalkaline type, whereas the anorogenic magmatic rocks comprise both subalkaline granitoids (of K series) and alkaline granites (of Na series), which are intensely fractionated and strongly enriched in incompatible elements. A-granitoids in the Aldan Shield and its surrounding folded structures were derived from mixed mantle-crustal sources. The sources of the subalkaline granitoids were dominated by the material of the continental lower crust, while the alkaline granitoids were derived from mantle sources. Thereby the mantle source material of the anorogenic granitoids consisted of an OIB-type component, and the postcollisional granitoids were derived from MORB and OIB sources. [ABSTRACT FROM AUTHOR]

The article focuses on the study on which aims to determine the Riphean age of zircons from alkaline syenites of the Karsakpai massif of South Ulutau in Central Kazakhstan with the uranium-lead (U-Pb) method. It mentions that the granitoids varying in chemical composition associated with Precambrian metamorphic strata were considered as coarse-grained gneissic granites (Zhaunkarskii complex), porphyroblastic granite-gneisses, and sub-alkaline potassic granites (Aktas complex). It states that the characteristics features of syenites of the Karsakpai granites and massif of the Aktas complex are massive structures and an absence of metamorphic transformations. Furthermore, it says that the age of intrusion of the massif allows to consider more ancient metamorphic complexes as Pre-Riphean.

The article discusses the tectonic position and age of volcanic and granites in the Eastern Margin of the Selenga. It cites the plutonic belt of Vitim volcano in Selenga. It mentions that geochemical and geochronological investigations were performed for the development of volcano-plutonic rocks in the western flank of Vitim volcano-plutonic belt. It states that acid rocks of alkaline and calc-alkaline represents the volcanic of Kuitun Formation. It adds that the volcanic composition and age of the Kuitun Formation and Nerchugan Complex's granitoids are close to volcanic rocks of the Vitim volcano-plutonic belt in the Selenga.

In the structure of west Kyrgyz Ridge (North Tien Shan), a great role is played by complexly dislocated Upper Precambrian-Cambrian terrigenous-carbonate and shale strata, as well as by granitoids that comprise several coupled WNW-striking synforms and antiforms, the largest of which is the Makbal antiform. Southeast of the core of this antiform, granitoids comprise the large Kara Dzhilga massif and several massifs that are of lesser size and have tectonic correlations with the hosting terrigenous-carbonate strata. In the Kara Dzhilga massif, the rocks of three penetration phases are distinguished; contacts between rocks are often of tectonic character. The early phase is presented by monzonite and monzodiorite; the main one, by large-porphyric biotitic granites; and the additional one, by aplitic granites and pegmatites. By the chemical composition, granites of Kara Dzhilga massif of the main phase correspond to subalkaline granites of high-potassium calc-alkali series. The age of their crystallization (zircon-based U-Pb method) is 1131 ± 4 Ma (Stenian). The formation of Stenian granitoids in the North Tien Shan may be related to development of Grenville fold belts, whose fragments were identified in the units of the Central Asian Belt. Tectonic correlations between these granitoids and hosting terrigenous-carbonate strata appeared as a result of immersion to significant depths and subsequent exhumation into the upper crustal horizons in the Early Ordovician. [ABSTRACT FROM AUTHOR]

The article offers information on the structural position and age substantiation of Middle Riphean gneiss granites of the Kokchetav Precambrian sialic massif in northern Kazakhstan. It says that the gneiss granites studied in the central areas of Kokchetav Massif such as Kokchetav, Chaikino Settlement, and Lake Chelkar have the development of small blocks and boundinized amphibolite, eclogite, and garnet amphibolite. It states that gneiss granites had structural-metamorphic alterations which transformed into blastomilonites with augen structure and well-developed linearity. Moreover, the age estimate of gneiss granites using uranium-lead (U-Pb) geochronological measurements corresponds to the age value of 1148 ± 8 Ma as deterrmined by discordia for zircon isotope composition.

The article presents a study which discusses uranium (U)-lead (Pb) geochronological dating of Paleozoic era granitoide rock formation of the Kiviliyskii complex in the Bureya Terrane in Russia. It says that porphyroblastic granites and rare quartz diorites from the Kiviliyskii massif were used as samples, in which accessory zircon crystals were selected and were subjected to multiple removal of surface contamination with ethanol, acetone, and nitric acid (HNO3). It says that Krogh's modified procedure was used for the chemical decomposition of zircon and U and Pb separation and isotope analyses were performed with the use of the MAT 261 multicollector mass spectrometer from Finnigan Corp. Results show that the granitoides in the site have an early Paleozoic era age.

The central portion of the Aldan Shield hosts very widely spread Archean and Early Proterozoic granitoids, much of which are granite-gneisses. Geochemical lines of evidence, data on inclusions in minerals, and Sm-Nd isotopic geochemical data suggest that the protoliths of granite-gneisses in the central part of the Aldan Shield were granitoids that had various composition, age, and were derived from distinct sources and under different parameters and were then emplaced in different geodynamic environments. The granitoids belong to at least two types of different composition that occur within spatially separated areas. The protoliths of granite-gneisses in the western part of the Western Aldan Megablock and the junction zone of the Chara-Olekma and Aldan geoblocks (granite-gneisses of type I) had the same age and affiliated to the same associations as the within-plate granitoids of the Nelyukinskii Complex. Their parental melts were derived at 2.4-2.5 Ga by the melting of Archean tonalite-trondhjemite orthogneisses of the Olekma and Aldan complexes. The protolith of granite-gneisses in the eastern portion of the Western Aldan Megablock (granite-gneisses of type II) can be subdivided into two groups according to their composition: granitoids with geochemical characteristics of subduction- and collision-related rocks. The protoliths of the type-II granite-gneisses with geochemical characteristics of subduction granitoids were produced simultaneously with the development of the Fedorovskaya island arc (at 2003-2013 Ma), whereas the protoliths of the type-II granite-gneisses with geochemical characteristics of collision granitoids were formed in the course of accretion of the Fedorovskaya island arc and the Olekma-Aldan continental microplate at 1962-2003 Ma, via the melting of magmatic rocks of the Fedorovskaya unit and older continental crustal material. [ABSTRACT FROM AUTHOR]

Abstract: According to U–Pb dating, the granitoids of the Tyrma–Bureya complex in the northern Bureya–Jiamusi superterrane of the Central Asian fold belt are not of Paleozoic, as previously thought, but of Mesozoic age (Nizhnyaya Stoiba massif, 218 ± 2 Ma; Talakan and Ust’-Dikan massifs, 185 ± 1 Ma). They formed at the early stages of collision between the North Asian and Sino-Korean cratons and the intervening Amur superterrane. [Copyright &y& Elsevier]

The article offers information on the results of the dating of alkaline granitoids of the Ulug-Tanzek Massif deposit in Tuva, Russia through uranium-lead (U-Pb) method for zircon and Argon-Argon (Ar-Ar) method. A sample from polylithionite-bearing ribeckite granite was studied for Ar-Ar geochronological investigations, in which, results revealed that approximately 85% of Ar that has clearly formed reflected three-step plateau with an age of 296 plus-minus two million years (Ma). In U-Pb dating, a sample of muscovite quartz-albite-microline granite with a netlike texture was used, in which, the determined age of 301 plus-minus three Ma, is similar within the error limits of the age estimation for the first sample using Ar-Ar method.

A number of plutons of charnockitic and granitic rocks have been revealed in the West Lithuanian Granulite Domain in the course of the recent geological mapping. The largest, Kuršiai (Curonian), batholith has been identified by gravity and magnetic anomalies and drill cores of 86 wells. Intrusions are composed of rocks of intermediate to felsic composition systematically attributed to charnockite, enderbite, mangerite, opdalite and granite. Rocks, characterized by 53 new ICP-MS and ES analyses, combine geochemical patterns characteristic both of A and S type granites being predominantly ferroan, alkali-calcic and calc-alkaline, high potassic to shoshonitic, but at the same time mainly peraluminous. Four U-Pb ID-TIMS zircon dates suggest formation of a charnockitic-granitic suite at around 1.85-1.82 Ga, presumably in the transitional period from the late orogenic to cratonic stages of formation of the continental crust. [ABSTRACT FROM AUTHOR]

Geological and geochronological U–Pb (zircon ID-TIMS) and 40 Ar/ 39 Ar (amphibole) data were obtained for six anorogenic magmatic associations in the Gobi Altai, southwestern Mongolia, in order to reveal its relationships with Late Paleozoic tectonothermal events in the southern part of the Central Asian Orogenic Belt (CAOB). In the Gobi Altai massifs of alkaline granites and grabens filled with bimodal volcanic suites occur as a chain 450 km long east–southeast direction. The massifs and volcanic fields are controlled by contacts of pre-Ediacaran continental crustal blocks with Late Neoproterozoic–Cambrian juvenile ophiolite and arc-type complexes of the Lake zone. Gobi Altai alkaline granites bear sodic-rich mafic silicate minerals and possess typical properties of ferroan A-type granites. Our geochronological data constrain emplacement time of the Gobi Altai alkaline granites and bimodal volcanic rocks at 293 ± 1–279 ± 1 Ma. This age interval coincides with timing of the emplacement of I-type granites (with a few S-type granites) and gabbroic intrusions in the Mongolian and Chinese Altai as well as with numerous massifs of A-type granites, layered mafic–ultramafic intrusions, and eruption of bimodal volcanic rocks between the southern edge of the Siberia craton and the northern margins of the Tarim and North China cratons. Hence, the Gobi Altai anorogenic magmatic complexes were produced by a large-scale Late Paleozoic magmatic event (or events) that encompassed a wide spectrum of terranes in CAOB. The most realistic models explaining these magmatic processes are: (i) the effect of the Tarim mantle plume, (ii) slab (or slabs) break-off after subduction blocking due to accretion of terranes of various types. [ABSTRACT FROM AUTHOR]

Jabel Sayed, in the northern part of the Arabian Shield, is an alkaline granite complex. It consists of syenogranites and aegirine–riebeckite alkali feldspar granites intruded into an older granodiorite–tonalite suite. Elemental geochemistry attests that the syenogranite and the alkali feldspar granite represent a genetically related post-collisional A 2 -type granite intrusion (e.g., high K 2 O + Na 2 O, FeO ∗ /MgO, Ga/Al, and Y/Nb, and low CaO, Ba, and Sr). U–Pb zircon dating and Nd isotopes of the alkali feldspar granites indicate an age of 593 Ma, εNd( t ) values of +4.9 to +5.3 (mean = +5.1), and depleted mantle model ages ( t DM ) between 0.78 and 0.88 Ga. These isotope results are in agreement with a juvenile magma source of Neoproterozoic age like that responsible for forming most other Arabian–Nubian Shield crust. The alkali feldspar granites have substantial modal content of albite and fluorite, wide variation of HFSE and REE and exhibit tetrad effects in REE patterns that indicate interaction with hydrothermal F-rich fluids. The fluids caused secondary metasomatic alteration superimposed on the granitic rocks. The result of the fluids–granitic rock interaction is a metasomatic pegmatite rim, which carries economic levels of HFS elements and REE, and a red granite variety (altered syenogranite) characterized by large variation in trace element abundances. Geochemical features in the granitic rocks such as strong linear positive correlation of Ta versus Nb and Zr versus Hf indicate magmatic origin of the fluids and emphasize that the behavior and enrichment of Ta and Nb are largely controlled by magmatic processes. Based on the geochemical and Nd isotopes compositions, we propose an origin for the Jabel Sayed granites which involved fractional crystallization of a parental magma derived by the partial melting of a crustal protolith accreted between 780 Ma and 880 Ma. This crustal protolith has juvenile geochemical and isotopic composition and was extracted from a subduction modified mantle source. [ABSTRACT FROM AUTHOR]