We present the results of study of the geologic structure, petrologic composition, and age of plagiogranitoid associations in the east of the Kaa-Khem batholith (Eastern Tuva). The batholith is located in the junction zone of the Tannu-Ola island arc (TIA) of Vendian-early Cambrian age and the Precambrian rocks of the Tuva-Mongolian microcontinent (TMM). Plagiogranitoids of this region formed in an accretion-collision setting in the period 490-450 Ma. Three stages of formation of plagiogranitoid associations have been established (similar to 489, similar to 476, and similar to 450 Ma). The plagiogranitoid associations in the east of the Kaa-Khem batholith do not differ in petrologic composition and age from the plagiogranitoid associations (500-450 Ma) in the west. Xenogenic zircons in the studied plagiogranitoids of the eastern Kaa-Khem batholith have ages of 2335-517 Ma. Their ages are divided into several clusters (524-517, 549-536, 615-586, 684-647, 739-735, 810-794, 842-827, and 2335 Ma) reflecting the heterogeneity of the crust in the TIA-TMM junction zone. The wide range of ages and the abundance of xenogenic zircons in plagiogranitoids of the eastern Kaa-Khem batholith testify to the contribution of older crustal sources to the granite formation at all stages of accretion-collision processes (from 490 to 450 Ma). The much narrower age range of xenogenic zircon (616-474 Ma) and its low contents in coeval plagiogranitoids of the western Kaa-Khem batholith are consistent with their localization within the TIA and the relative homogeneity of the crust in the area of felsic-melt generation. In the west, the influence of older crustal sources was insignificant and manifested itself only at the final stage (similar to 450 Ma) of accretion-collision processes.

Based on the isotope-geochronological (zircons, U-Pb method), petrogeochemical, and structural and petrologic data, the following paper provides a detailed description of the characteristics of the Late Paleozoic basic and granitoid magmatism in the eastern part of the Kaakhem magmatic area (Eastern Tuva). During the formation of the Shivey alkaline-granitoid and Chadal gabbroid massifs in the period of 292–283 Ma, there were revealed two stages of contrasting magmatism. The early stage is characterized by the formation of plutonic mingling structures and intermediate rocks. Deformation structures, widespread in the early-mingling rocks, are superimposed and formed in extensional regime. At a later stage, there occurred a sequential intrusion of salic and mafic magmas into the zones of local extension in the early-mingling host rocks. A similar petrogeochemical composition of basic rocks of the early and late mingling indicates that they all formed from enriched magma. Granosyenites and granites are derived from melting of tonalities and metasedimentary rocks with a significant contribution of the mantle component. The simultaneous formation of the Chadal gabbroid and Shivei granitoid massifs took place at the intraplate stage of the development of geological structures of Eastern Tuva in the Late Paleozoic.

The Cambrian Kharly alkaline plutonic complex composed mainly of foidolite and nepheline syenite makes up a small intrusive field in the Sangilen Plateau in Tuva (southern Siberia). The rocks show large ranges of major oxides (38-58 wt% SiO2 ; 1-18 wt% Na2O + K2O; 11-28 wt% Al2O3; 1.5-20 wt% CaO; 0.1-8 wt% MgO; 2-12 wt % Fe2O3) controlled by variable percentages of minerals: clinopyroxenes, calcic amphiboles, micas, nepheline and feldspars. Alkaline rocks are cut by carbonatite veins composed of predominant calcite coexisting with femic minerals (10-15% of aegirine-ferrosalite-hedenbergite, sodic-calcic amphiboles, ferrobiotite, Ti-garnet), Na-K feldspar and nepheline (up to 15-20%), fluorapatite (up to 20-25%), Sr-apatite, and accessory carbocernaite, titanite, Ti-magnetite and ilmenite. Carbonatites (4057-8859 ppm Sr, 426-1901 ppm Ba (Sr/Ba >= 2), 290-980 ppm REE + Y, 2 to 100 ppm Zr, and 0.5 to 15 ppm Nb) possibly originated at high (>= 500-650 degrees C) temperatures as a result of liquid immiscibility. The isotope systematics of rocks and minerals (epsilon(Nd)(t) from similar to 2.9 to 6.5; Pb-20(7)/Pb-20(6)in = 0.89; (208)pb/Pb-206(in) = 2.15; Sr-87/Sr-86(t) = 0.70567-0.70733, delta O-18(v-smow) approximate to 7.2-19.5 parts per thousand, and delta C-13(v-PDB) from -6.0 to -1.4 parts per thousand) suggest mixing of PREMA and EM 1 material during magma generation and crustal contamination of the evolving melts. The rocks bear signatures of interaction with "magmatic-equilibrated" fluids or heated meteoric waters. LILE/HFSE ratios indicate mixed magma sources that involved the material of IAB and OIB, as well as a crustal component, possibly, due to interaction of a mantle plume with rock complexes on the active continental margin.

—The Paleozoic foidolite–foyaite plutons of the Sangilen upland (Bayan-Kol, Dakhu-Nur, Chik, and Kharly ones) might have formed in the Late Cambrian–Early Ordovician (~490–500 Ma, Sm–Nd and U–Pb); they are the result of the oldest alkaline magmatism in southeastern Tuva. The intrusion was accompanied by the formation of high-temperature (up to ~600–900 ºC) endogenous carbonate rocks containing calcite, alkali pyroxene, Na–Ca amphibole, biotite, fluorapatite, microcline, and nepheline. Silicate and carbonate derivates were produced, most likely, from genetically related heterogeneous sources with εNd(T) varying from 3.0 to 6.3 and from –0.5 to 6.5, respectively, which might be due to the mixing of the depleted (PREMA) and enriched (EM) mantle materials. Initial ratios 207Pb/206Pb ≈ 0.89 and 208Pb/206Pb ≈ 2.15 in K-feldspar from calcitic rocks are close to those of EM 1. The correlation between the stable-isotope ratios (δ18O ~ 7.2–19.5, δ13C from –6.0 to –1.4‰) and the high 87Sr/86Sr(T) ratio (0.7057–0.7076) indicates a significant crustal contamination of magma in the upper horizons of the lithosphere and a minor impact of a meteoric fluid. The assumed synchronous formation of the studied plutons and other alkaline rock complexes of the Early Paleozoic Large Igneous Province in the west of the Central Asian Orogenic Belt as well as their isotope similarity do not rule out that the intrusion took place in the plume–lithosphere interaction setting.

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.

The link of lithogenesis with granitogenesis is gradually substantiated. The role of atmosphere and hydrosphere is pointed out in the maximum efficiency of exogenous processes that caused the differentiation of the basaltic crust and the formation of the sedimentary crust. The origin of water and oxygen on the Earth is explained. The role of the eutectic is described in the formation of likecomposition granite melt and as consequence, the formation of an intergranular eutectoid granite melt that further the continuous process of granite formation under the certain thermodynamic and geodynamic conditions.

The Kaakhem (> 30,000 km(2)) is one of the major magmatic areal within the Altai-Sayan folded area (Eastern Tuva, Russia). Formations of the Kaakhemsky area were more than 250 million years with change of geotectonic conditions. The last stage is bound to intraplatform magmatism (300 Ma ago). Massifs of bimodal association - gabbroic and alkaline granitoids particularly the Chadal gabbroic and the Shivey alkaline granite-quartz-syenite massifs were formed as a result of its activities within the Kaakhem magmatic areal. The object of the study are rocks breccia-like and drip-like structurs in the contact zone of the alkali-granitoid Shivey and gabbroid Chadal massifs in the Kaakhem magmatic. Predecessors repeatedly noted that such structurs relationships have typical features of mingling: flexuous, scalloped contours of mafic bodies with orientation of protrusions towards granitoids; oval, rounded form of basal fragments; signs of plastic deformation in the basices and others. Geochemical analysis of rare and scattered elements contents in contact zone rocks showed strongly marked character of hybridization. Results of scanning electron microscope analysis and X-ray microanalysis let consider the probable sequence of mineralization in contact zone of massifs of bimodal association of gabbroic and alkaline granitoids of the Kaakhem magmatic areal. Relationship established between microtexture and geochemical inherity indicate the interaction of basic and granitic magmatic meits and it was formation of middle group rocks.

U–Pb geochronological studies of garnet of the andradite–morimotoite series and Sm–Nd geochronological studies of this garnet and apatite from the Chikskii Massif (Tuva-Mongolia microcontinent) were carried out. The garnet studied is characterized by relatively high concentrations of U (14–16 ppm) and by a low level of common Pb (Pbс/Pbt = 0.07–0.1). The concordia age of garnet is 492 ± 2 Ma (MSWD = 0.01, probability 92%) and matches within the error with the Sm–Nd age determined by the isochrone for apatite, garnet, and bulk rock (489 ± 9 Ma, MSWD = 0.86). This allows us to consider calcic garnets of the andradite–morimotoite series as promising mineral geochronometers for U–Pb dating of ultrabasic alkaline rocks.

The research is aimed at proving the age, nature of parental magma sources, and geodynamic conditions, under which alkaline intrusives of the Tuva Mongolian terrain were introduced. That is relevant when reconstructing development of the Paleoasian Ocean and Paleozoic magmatism in folded frames of the Siberian Craton. The studied Dakhunur intrusion of ultrabasic foidolites and foyaites in the Sangilen Upland is an Early Carboniferous derivative of a Paleozoic alkaline magmatism of the South-Eastern Tuva. According to the precision isotopic Ar-Ar data obtained for the first time, its formation took place ~ 328 Ma. Geochemical features of alkaline rocks of pluton revealed by ICP-MS method indicate the intrusion occurred in a difficult geodynamic environment, where mantle plume interacted with accretionary complexes of active continental margin. Based on this fact, the duration and conditions of a tectonic regime of formation of one of the largest igneous provinces in the Central Asian folded belt are estimated.

Tuvino-Mongolian massif is held to be one of largest massifs in a structure of the Central-Asian Fold Belt fringing the Siberian Platform on the south and south-west. Such massifs with the crystalline basement are considered as microcontinents - fragments of continental massifs, included in the supercontinent Rodinia and attached to structures of surroundings of the Siberian Platform in the course of the Paleoasian ocean development. New information on development of endogenous processes in the Tuvino-Mongolian massif has been obtained from recent investigations. Features of geological setting of metamorphic complexes (Naryn, Moren, and Erzin complexes) have been studied. The Naryn complex is made of essential carbonate, terrigenous-carbonate, and terrigenous piles of the Balygtyglchem, Chartys, Naryn, and Chinchilig formations. These rocks are attributed to deposits of epicontinental shelf seas. The Moren complex includes volcanic and sedimentary rocks metamorphosed in the conditions of the amphibolite facies and formed in the environment of rifting structures of passive continental margins. The Erzin complex is made of biotite and garnet-biotite gneisses, intense migmatitized, with relicts of the granulitic facies. Their protoliths were sedimentary rocks typical of basins of passive continental margins. Hypersthene and bipyroxene crystalline schists of the Lower Erzin tectonic plate are attributed to the Erzin complex too. The initial rocks of the schists can be considered as fragments of paleoisland-arc and paleoocean formations. U-Pb dates (SHRIMP) of detrital zircons from metaterrigenous rocks of the Moren complex are 750 M.a. and of the Erzin complex - 800 and 900 M.a. This determines a lower age boundary of rocks accumulation.

The Snezhnoe phenakite-beryl deposit is one of the highest-grade deposits in the Altai-Sayan beryllium province. This deposit is spatially associated with the alkali granite of the Ognit Complex and localized in the apical part of the granitic pluton. The trace element composition of granite, as well as of Be and Ta-Nb ores was studied. The Rb-Sr age of Be mineralization estimated at 305 Ma is consistent with the time of formation of numerous rare-metal alkali granitic plutons in the Eastern Sayan and the eastern Tuva. The region of these granitic plutons is outlined as the Late Paleozoic East Sayan rare-metal metallogenic zone specialized for Nb, Ta, Be, Li, Zr, Th, and REE mineralization. The East Sayan zone is localized in the marginal part of the Barguzin igneous province and is similar to the marginal zone of this province in composition of igneous associations and metallogenic specialization. The formation of the Barguzin igneous province and the East Sayan metallogenic zone is related to the evolution of the Late Carboniferous-Early Permian mantle plume.

Одним из богатейших месторождений Алтае-Саянской бериллиеносной провинции является Снежное фенакит-берилловое. Оно пространственно ассоциирует с щелочными гранитами огнитского комплекса и расположено в его апикальной части. Изучен редкоэлементный состав огнитских щелочных гранитов, бериллиевых и Nb-Ta-руд месторождения. По полученным Rb-Sr-изотопным данным, возраст бериллиевого оруденения на месторождении Снежное – 305 млн. лет. Полученный возраст согласуется со временем образования многочисленных массивов редкометальных щелочных гранитоидов в Восточном Саяне и в Восточной Туве. Область распространения этих гранитоидов выделена как позднепалеозойская Восточно-Саянская редкометальная щелочногранитная металлогеническая зона, специализированная на Nb, Ta, Be, Li, Zr, Th, REE оруденение. Восточно-Саянская зона возникла в периферической части Баргузинской магматической провинции и по составу магматических ассоциаций и металлогенической специализации подобна другим периферическим зонам этой провинции. Образование Баргузинской магматической провинции и Восточно-Саянской металлогенической зоны связывается с формированием мантийного плюма в конце карбона–начале перми.

Geological, petrologeochemical, and geochronological studies of the rocks from the Shivei alkali-granitic pluton were conducted. A pluton about 500 km 2 in area is a part of the larger (more than 30 000 km 2 ) Kaakhem magmatic area. The data obtained allow us to characterize the magmatic complex of the Shivei pluton as a bimodal association with picrobasalts, subalkali basalts, and subalkali and alkali granitic rocks differentiated from syenites to leucogranites. The SHRIMP_II zircon dating from quartz syenites and alkali granites indicate the Permian age of the pluton (293.8 ± 3.8 Ma and 297.1 ± 3.8 Ma, respectively). Mafic-alkali-granitic associations similar in age and type, which are traced in the meridional direction along the Eastern Sayan toward the Siberian Platform, were distinguished as the Eastern Sayan zone of the Late Paleozoic alkaline magmatism. Its location corresponds to the western periphery of the Angaro-Vitim batholite and fits well into the zonal structure of the Barguzin magmatic province. We relate the geodynamic position of the Barguzin province with the mantle plume that was overlapped by the edge of the Siberian Pale-ocontinent in the course of its Paleozoic migration above the African hot spot.