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The paper presents new original data on the Devonian felsic volcanism of the NW Rudny Altai (Russia) in the west of Central Asian Orogenic Belt (CAOB) – the front part of the Altai convergent margin of the Siberian continent. Two geochemical types of subvolcanic rhyolites were emplaced synchronously with the bimodal rhyolite-basalt association, which began to form in the end-Emsian, and clearly manifested on the border of the Givetian and the Frasnian. The rhyolites yield zircon U-Pb ages of ca. 390 Ma (R1-type) and 380 Ma (R2- and R3-types), reflecting two peaks of the volcanic activity. Most of these rocks have extreme petrochemical characteristics of high SiO2 contents and have contrast Na/K ratios. Their compositions are transition between calc-alkaline and tholeiite series: (La/Yb)n ~ 2–7, Zr/Y ~ 4 (Zr 350 ppm), Zr (>250 ppm), and high Ga/Al (>2.6) values. The island-arc-like R1-rhyolite formed immediately after the beginning of rifting due to widespread crustal melting under reduced conditions. The generation of rift-like R2- and R3-rhyolites took place under non-equilibrium conditions, synchronously with the rise in the upper crust of Givetian-Frasnian basic magmas, as a result of the active lithospheric extension and high thermal input from the underlying hot mantle. We propose an extension regime in the transition area between the island-arc and back-arc basin for the origin of rhyolites. The study of the Devonian volcanism of the Rudny Altai gives important information about the processes that occurred at the initial stage of the formation of the Altai convergent margin.

The paper presents the results of geological, geochemical and isotope-geochronological studies of subvolcanic rhyolites of the Western Gorny Altai and Rudny Altai which have related to two large volcanic systems, the Altai-Minusinsk and Altai-Salair, respectively. The results of U-Pb isotopic dating of zircons revealed two groups of ages ~410-405 and 390-381 million years. Isotope-geochemical characteristics of rhyolites show relatively high values of εNd(T) = +2,7...6,0 with relatively young values of model ages T(DM) = 851-966 Ma in the Rudny Altai and more ancient - up to 1266 Ma in the West Gorny Altai. Geochemical characteristics indicate that its composition is consistent with transitional field between within-plate and island-arc felsic magmas. The results obtained correspond to the two-stage evolution of volcanism and its migration from the continent to the ocean.

The paper presents new original data and a review of previous studies on the Late Carboniferous – Early Permian granitoids of the Kunush and Kalguty intrusive complexes from the Kalba fold belt (East Kazakhstan). These rocks formed at the initial post-collisional stage of the Irtish-Zaisan orogen in the western Central Asian Orogenic Belt (CAOB). The granitoids form isometric or NW linear intrusions inside the Late Devonian - Early Carboniferous metasediments which overlap the accretionary lithology of the Kalba fold belt in front of the Altai active margin of the Siberian continent. These granitoids contain zircon grains with U-Pb ages of ca.308–291 Ma, synchronous with the peak post-orogenic magmatic event at ∼300 Ma in the CAOB. The Kunush high-Na granitoids, with high SiO2 (67–72%) and Al2O3 (15–18%) contents and the Na2O/K2O ratio (1.94–6.43), and low HREEs (Yb = 0.22–0.93 ppm) but moderate Sr/Y ratios (47–179), Mg# (35–55) and Ni, Cr, are generally common to high-Al TTG-series with non-subduction geochemical signatures. The Kalguty granitoids mostly belong to calc-alkalic to subalkalic high-K series, have non-corundum CIPW-norm compositions and mainly weakly peraluminous (ASI = 0.97–1.09) characteristics. Their Fe∗ = 0.7–1 at 62–74 wt.% SiO2 and relatively high Y/Nb (2–4) and Rb/Nb (9–18) ratios are similar to transitional compositions reported for fractionated I- and A2-type post-orogenic granites worldwide. The Kunush high-Na and Kalguty high-K granitoids formed at different depths in the crust and the parent melts were derived from metabasaltic (MORB; P = 10–15 kbar) and metagranitic (TTG-like; P

We studied the geologic position, mineralogy, petrography, chemical composition, and age of granitoids of the Gamov batholith located in the Heilongjiang-Grodekovo terrane, southern Primorye (Russia). The studies have revealed four intrusive rock phases, from gabbro to leucogranites, in the massif. U–Pb zircon dating of tonalites of phase II and leucogranites of phase IV (254 ± 4 and 259 ± 2 Ma, respectively) shows that the intrusion of granitoids took place in the Late Permian without a significant gap in time. Structural investigations gave evidence for the intrusion in the E–W compression setting. Geochemical studies have revealed granitoids of strongly different compositional types in the intrusive massif: gabbroids, quartz diorites and tonalites with characteristics of low-alumina TTG, calc-alkalic granodiorites and I-type granites, and moderately alkaline leucogranites. The obtained data, together with the results of previous research into the Permo-Triassic granitoids of southern Primorye, reject their formation as a result of the evolution of the Solonker oceanic structures and suggest a more intricate tectonic scenario, which calls for additional study.

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).

The geologic position, age, petrologic composition, and petrogenesis of mesoabyssal plagiogranites in northern Rudny Altai, dated earlier at the Early–Middle Devonian, are considered. The Middle Carboniferous (322–318 Ma) age of granitoids has been substantiated by isotope-geochronological data (U–Pb zircon dating and Ar–Ar amphibole and biotite dating). Geologic-structural studies showed that the intrusion of granitoids took place at the time when compression was changed by sinistral faulting. This led to the conclusion that the granitoids formed at the peak of the collision between the Siberian and the Kazakhstan paleocontinents. Geochemical and isotope studies showed that most of the analyzed plagiogranites belong to high-alumina (continental) type and resulted from the deep melting (~ 15 kbar) of metabasic substrates compositionally similar to N-MORB (judging from results of geochemical modeling and the Nd isotope composition). The presence of plagiogranites of low-alumina (oceanic) type in the postgranite dike series testifies to the melting of the Rudny Altai heterogeneous crust at different depths during its collisional thickening.

We consider the geologic occurrence and PT-conditions of the generation and crystallization of siliceous melts that formed volcanic structures within the Altai collisional system of Hercynides. The data on the geologic occurrence, internal structure, and petrogeochemical age of rocks are presented, as well as results of the thermobarogeochemical studies of inclusions in minerals. The performed investigations showed the presence of siliceous dacitic melts in the studied volcanic structures. These melts were generated in the lower crust (~10 kbar, 1000–1200 oC) as a result of the partial melting of crustal substrates under the influence of high-temperature mantle melts.

New structural and petrological data have been obtained for the zone of Siberia-Kazakhstan oblique collision for Permian time. In terms of classical tectonics, the area coincides with the Zaisan folded area produced by closure of the Char paleo-ocean in the Late Carboniferous. However, the extent, structure, and composition of magmatism at the Carboniferous-Permian (280±10 Ma) and Permian-Triassic (250±5 Ma) boundaries require an active control from Morgan-type lower mantle plumes (Tarim and Siberian plumes). Structure formation in the lithosphere and heat sources of magmatism have been simulated in a 3D model including lithospheric strain rates (with regard to viscosity layering) and subcontinental upper mantle convection. According to our model, heat supply from slab break-off and/or delamination of lithosphere is insufficient to maintain large-scale mantle-crustal magmatism in the case of oblique collision between 80–100 km thick plates (“soft collision”). The Late Paleozoic-Early Mesozoic Altai is considered as a model of a large hot shear zone, a particular structure produced by interference of plate- and plume-tectonic processes. Special attention is given to structural and petrological markers of plume tectonics (reported for the case of the Altai collisional shear system), with their diagnostic features useful for understanding geodynamics of other similar regions.