Metamorphic core complexes (hereafter MCC) revealed in the Transbaikalia have similar features of their patterns. Three levels can be distinguished by structuralmaterial indicators: core, zone of mylonites (dynamically metamorphosed rocks) and overlying formations. The cores are composed of the Paleozoic granites and granitogneisses. Zones of mylonites skirt the cores and are characterized by various tectonites which are formed at the expense of the core rocks. The overlying formations include volcanogenicsedimentary series of the Mesozoic and the Upper Palaeozoic. The rocks are not metamor phosed, yet subject to brittle deformations. Structurally, they are detached and deposited above the zone of mylonites. In Transbaikalia, MCC are characterized by synmetamorphic structural paragenesises of one type: lowangle schistosity, micro and macrostructures (folds, mineral streaking, boudinage, pressure shadows, C-S structure, kickbends). According to the kinematic analyses, they were formed by the simple shear mechanism along the zones of deeply penetrating regional dislocations which plunged in the southeastward direction. Tectonic transportation of the materials developed in the same direction, i.e. the top parts of tectonostratigraphic sections were displaced against the lower parts in the southeastward di rection. Extension deformations tended in the northwest-southeast direction. Such movements facilitated formation of synthetic listric normal faults and rift basins. The most intensive tectonic exposure period is determined as 112-123 mln years, while the period of metamorphism is assessed as 140-130 mln years. The rocks in depth of the deep dislocation were transformed in conditions of amphibole facies of metamorphism (Т=590-640 °С; Р=3.2-4.6 kbar).

We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.

Metamorphosed volcanic rocks of the Ushmukan suite were studied in the Mukodek gold­ore field located in the Baikal­Muya belt in the Northern Baikal area, Russia. The Ushmukan suite shows interleaving of ortoschists which composi­ tions are widely variable. Basalt­andesite­dacite series of normal alkalinity are the substrate of the studied metavolcanic rocks. Based on the set of geochemical characteristics, it is concluded that the rocks were formed in suprasubduction geody­ namic conditions corresponding to a mature island arc. The proximity of the geological locations and the similarity of the geochemical characteristics of the volcanic rocks of the Ushmukan suite and rocks of the Kelyan suite (Neoproterozoic, 823 Ma), which have similar compositions, give grounds to consider these two rock suites as age peers. Specific features of gold distribution through the Mukodek gold­ore field are analyzed. Industrial gold contents are recorded only in berezite­ listvenite metasomatic rocks of the gold­quartz­sulfide formation which were formed on metavolcanic rocks of the Ush­ mukan suite. It is concluded that the volcanic rocks, which are specific of the island­arc setting, could be a source of gold for deposits in the Mukodek gold­ore field.

The petrographic, lithogeochemical and U-Pb (LA-ICP-MS) geochronological studies were carried out to investigate the terrigenous rocks sampled from the lower part of the Ipsit suite of the Karagass series (Sayan segment of the Sayan-Baikal-Patom belt). These rocks include sandstones, aleurite sandstones and aleurolites, and their mineral compositions are close to that of arkose. Most of the studied rock samples show petrographic features typical of the epigenetic changes at the stage of catagenesis: regeneration of quartz clastic grains, pelitization of potassium-feldspar clastic grains, occurrence of clay-hydromica aggregate, sericitization of plagioclase, chloritization of biotite, and silicification of dolomite pieces, and occurrence of authigenous tourmaline. The above was confirmed by the analysis of the concentrations of petrogenic elements in the studied rocks from the lower part of the Ipsit suite. The analysis results show that the concentrations of K2O are elevated, while the concentrations of Na2O are relatively very low, which may be due to the redistribution of these elements during epigenetic transformations. According to the classification by genetic types on the basis of the system of petrochemical modules, the rocks of the lower part of the Ipsa suite are of the petrogenic nature. The acidic igneous rocks are dominant in the source area, as evidenced by the presence of granitoid and quartzite fragments in the clastogenic component, as well as the set of accessory minerals typical of the igneous rocks of the acidic composition, and the distribution pattern of rare and trace elements. According to the U-Pb (LA-ICP-MS) dating of detrital zircons from the aleurite sandstone sampled from the lower part of the Ipsit suite, the zircons are exclusively of the Archean-Early Proterozoic ages. Such ages correlate with the age of the granitoids of the Sayan complex and the felsic volcanites from the Maltsev layer of the Elash series (Biryusa block). Furthermore, the detrital-zircon age spectra of the aleurite sandstone of the lower part of the Ipsit suite are identical to the detrital-zircon age spectra of the terrigenous rocks from the underlying strata of the Shangulezh and Tagul suites of the Karagass series. This study suggests that sedimentation of the Ipsit suite of the Karagass series took place due to the influx of detrital material from the southern part of the Siberian craton into the sedimentation basin, and the acidic igneous rocks of the Biryusa block were one of the main sources of detrital material.

The article reports on the geological, mineralogical, geochemical and isotope-geochemical studies of granitoids (charnockites) from the Tatarnikovsky massif located in the northern part of the Baikal uplift of the Siberian craton basement. The age of the studied granitoids is 1.85 Ga. Like other unmetamorphosed granitoids and associated volcanic, the granitoids dated 1.88-1.84 Ga are abundant in the southern area of the Siberian craton. These rocks are a part of the South Siberian post-collisional magmatic belt. The Tatarnikovsky granitoids form a series of small massifs confined to the Davan tectonic zone. However, unlike the rocks of the Davan zone, these granitoids have not been subjected to dynamometamorphism, mylonitization and metasomatism, and seem younger than the geologic structure of this zone. The formation of granitoids coincides in time with the youngest formations in the North Baikal volcanoplutonic belt (1.85-1.84 Ga). The Tatarnikovsky granitoids have two facies varieties-coarse-grained and medium-fine-grained porphyric, the transition being gradual. Considering the mineral composition of the granitoids, specifically the presence of orthopyroxene, these rocks can be classified as charnockites. The research results presented in this article are based on the study of charnockites in the Tatarnikovsky massif, the largest in the Tatarnikovsky complex. The chemical composition of the Tatarnikovsky coarse-grained granitoids corresponds to monzonite and syenite, and fine-grained porphyry granitoids are granosyenite. All the studied granitoids are close to alkaline and calc-alkaline, metaluminous (ASI=0.83-0.97), ferrous (FeO*/(FeO*+MgO)=0.86-0.89) granite, with high concentrations of Nb, Y, Zr, and Ba, and low concentrations of Sr. According to their geochemical characteristics, the Tatarnikovsky granitoids correspond to A-type granite. These rocks show negative values εNd(t)=-1.4…-3.5 and model age ТNdDM=2.4-2.5 Ga. The temperature estimated for the initial stages of crystallization of granitoid melts suggests that granitoids formed at high temperatures, 890-960°С (i.e. the zircon saturation temperature). The granitoid melts crystallized in hypabyssal conditions at the pressure of 2.2-2.9 kbar, as well as in conditions of low or moderate oxygen fugacity. According to the mineralogical, geochemical and isotope-geochemical data, the Tatarnikovsky charnockite could have resulted from melting of mafic rocks from the lower crust (gabbroid, and ferrodiorite) which are products of differentiation of the tholeiitic mantle magmas that had intruded into the base of the continental crust. Taking into account the high concentrations of Ba and the positive anomalies of Eu in the distribution spectra of rare-earth elements (REE) of the coarse-grained granitoids, it can be suggested that these granitoids are the products of partial melting of the crustal GEODYNAMICS & TECTONOPHYSICS