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Studies of volcanic rocks in orogenic troughs of Eastern Kazakhstan were carried out. The troughs were formed at late-orogenic stages of evolution of Hercynian Altai collision system. Volcanic rocks are represented by basalts, andesites, dacites and rhyolites. Based on geochemical and isotopic data, the basalts and andesites derived from mafic magmas that formed as a result of partial melting of garnet peridotites in the upper mantle under the orogen. U–Pb zircon data prove two volcanic stages: more-scaled Middle Carboniferous (~311 Ma) and less-scaled Early Permian (297–290 Ma). Basalts and andesites in lower parts of the orogenic troughs and independent dacite-rhyolite structures were formed at the Middle Carboniferous stage. Parental mafic magmas were formed as a result of partial melting of mantle substrates in local transtensional zones along large shear faults. The formation of dacites and rhyolites could have been caused by partial melting of crustal substrates under effect of mafic magmas. Transtensional movements in the lithosphere of orogenic belts may indicate the beginning of collapse of orogens. A smaller volume of basalts and andesites formed at the Early Permian stage. Geochemical data prove the independent episode of partial melting in upper mantle. Synchronous basalts and andesites also appeared at wide territory in Tian Shan, Central Kazakhstan, and Central and Southern Mongolia. Early Permian volcanism indicates general extension of the lithosphere at the postorogenic stages. Large-scaled Early Permian mafic and granitoid magmatism in Central Asia has been interpreted in recent years as the Tarim Large Igneous Province caused by Tarim mantle plume activity. Thus, the extension of the lithosphere and associated volcanism in the Early Permian can be an indicator of the onset of the plume–lithosphere interaction process.

Purpose. Study on the chemical composition of lake waters, salt brines, brine and bottom sediments to identify the mineralization of rare metals and other types of minerals. Methodology. Mass spectrometric studies (mass spectrometer with inductively coupled plasma ICP-MS 7500cx from AgilentTechnologies) for the purpose of high-precision analytical studies on the chemical composition of salt lake water in order to assess the content of rare elements. The use of unmanned aerial vehicles for linking and geometrizing lakes. Findings. Field surveys on the geometrization and linking of lakes were carried out. From the materials obtained with the help of the drone, orthophotoplans were created (with a measurement accuracy of up to 1 centimeter), as well as a digital terrain model and a digital terrain model. A complex of analytical works was carried out using inductively coupled plasma spectrometry. When analyzing the distribution graphs of the absolute content of micro-components in the waters of the lakes of the Delbegeteysky massif, it was found that all samples were enriched with sodium, phosphorus, iron, magnesium and barium. The results of the analyses revealed the predominance of sulfates and chlorides in the composition of the surface waters of most of the water bodies of the Delbegeteysky massif. At the Burabai site, lake waters are characterized by an alkaline reaction of the environment (on average = 8.71). At the same time, the salinity of water bodies varies from 05 to 9 g/dm3. Originality. Large-scale outcrops of granites of the Kalba complex (P1), with which a rare-metal type of mineralization is genetically associated, are known to be on the selected study sites. Quartz-wire-greisen and quartz-wire tin, tin-tungsten and tungsten formations are also widely developed. Considering the large geochemical migration ability of rare alkaline elements in the thickness of loose sediments as a result of intensive geodynamic processes in the East Kazakhstan region, it is possible to assume the possibility of their migration to the upper horizons and accumulation in salt lakes localized within the area of development of granite intrusions of Permian age and associated deep tectonic faults. Practical value. The results of the research can serve as a revival of the rare metal industry in the region, which will allow developing new high-tech industries and creating new jobs in this area. The obtained results can be used for setting up further exploration and operational work on the selected promising areas.

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

The Itmurundy zone of the northern Balkhash area is a Pacific-type orogenic belt. It possesses a complex geological structure and hosts rocks of mantle, accretionary and post-orogenic associations. The volcanic and sedimentary rocks of the accretionary association belong to three suites: Itmurundy (O1-2), Kazyk (O2-3) and Tyuretai (O3-S1). The suites are separated by tectonic unconformities or faults of three orders: 1) large regional faults; 2) medium faults separating mantle and oceanic accreted rocks; 3) small faults separating packages consisting of oceanic sediments. The Itmurundy Fm. (O1-2) is the most lithologically variable consisting of oceanic basalt, pelagic chert, hemipelagic siliceous mudstone and siltstone, and trench greywacke sandstone. The packages, each consisting of chert-siliceous mudstone, are separated from each other by 2nd and 3rd order faults of probably thrust nature, i.e. they are parts of duplex structures. The presence of duplex structures and the high degree of deformation of Itmurundy Fm. rocks are typical of accretionary complexes. The associations of volcanic and sedimentary rocks under study represent a full section of oceanic plate stratigraphy (OPS): basalt (MORB, OIB)—chert (pelagic)—siliceous mudstone, siltstone and shale (hemipelagic)—trench sandstones (greywacke). The structural position and the lithology of Itmurundy rocks accord well with the model of formation of accretionary complexes at Pacific-type convergent margins, in particular, those in the western Pacific.

The paper reports results of petrological-geochemical, isotope, and geochronological studies of the Preobrazhenka gabbro–granitoid massif located in the Altai collisional system of Hercynides, Eastern Kazakhstan. The massif shows evidence for the interaction of compositionally contrasting magmas during its emplacement. Mineralogical–petrological and geochemical studies indicate that the gabbroid rocks of the massif were formed through differentiation of primary trachybasaltic magma and its interaction with crustal anatectic melts. Origin of the granitoid rocks is related to melting of crustal protoliths under the thermal effect of mafic melts. The mantle–crust interaction occurred in several stages and at different depths. A model proposed here to explain the intrusion formation suggests subsequent emplacement of basite magmas in lithosphere and their cooling, melting of crustal protolith, emplacement at the upper crustal levels and cooling of the granitoid and basite magmas. It was concluded that the formation of gabbro-granitoid intrusive massifs serves as an indicator of active mantle–crust interaction at the late evolutionary stages of accretionary–collisional belts, when strike-slip pull-apart deformations causes the high permeability of lithosphere.

The western Baikal region (Ol’khon region, Nutgei zone, Kharikta area) is characterized by the development of packets of thrust-type folds and synkinematic granites corresponding to the stage of thrust deformations (overthrust-type granites). Two stages in the formation of thrust-type folds separated by episodes of granite emplacement are definable. The data obtained make it possible to estimate both the time of transition from thrust to strike-slip deformations and the duration of accretionary‒collisional events that resulted in regional strike-slip deformations, which terminated in the western Baikal region 460‒455 Ma ago.

This is a synthesis of published and new data on the Kalba batholith in Eastern Kazakhstan, the large granitic body in the western part of the Central Asian Orogenic Belt. The batholith consists of granodiorite-granite and leucogranite rocks discriminated on the basis of major- and trace-element chemistry and isotope systematics. The granodiorite-granite rocks, which form the bulk of the batholith, are compositionally variable and can be classified as mixed S-I-type granites. The leucogranites occurring as a few large intrusions in the northwestern part of the batholith have more stable compositions, with high contents of REE, HFSE, F, Li, and B, typical of A-granites. Judging by the isotope systematics of the Kalba granites, compared with that of their potential parent rocks from the Kalba-Narym zone and its surroundings, the two groups originated by different mechanisms in two magmatic events. The granodiorite-granites were produced by large-scale melting of crustal material, including the metabasaltic basement and overlying metavolcanic and metasedimentary rocks. The origin of leucogranites was associated with low-degree partial melting of the deepest Kalba-Narym sediments under the effect of fluoride fluids. The batholith formation spanned about 21 myr: granodiorites and granites formed in the 297–286 Ma interval and leucogranites between 288 and 276 Ma. The ages of the two events bracket the intraplate postorogenic stage of the CAOB history that was coeval to the formation of the Tarim large igneous province.

The Karaotkel deposit of fossil Ti-Zr placers is situated in the north-western edge of the Zaysan intermontane depression in Eastern Kazakhstan. The geological structure of the mineral sands is characterized by complex morphology and a two-layered assembly, formed as the result of long-term regional geodynamic processes during the Meso- and Cenozoic. Our study is aimed to establish a genetic model for the formation of the continental Karaotkel Ti-Zr placers by utilising novel data on geology, mineralogy, geochemistry and geochronology. Sedimentological facies analyses indicate an environment of coastal wave-built formation of the Late Cretaceous kaolin-dominated weathering crust and Paleogene sediments of the North Zaysan formation. A set of geochemical indices is applied on the base of key geochemical parameters of placer composition to allow quantitative and qualitative assessment and to establish genetic trends. Mineralogical composition of the heavy fraction of the productive sediments of the Ti-Zr placer (horizon “A” of the North Zaysan formation) was determined by XRD and microprobe-probe analyses. Microprobe analyses determined the elemental composition of mineral grains of zircon, ilmenite, monazite, staurolite, titanite, epidote and gold. Gold and monazite were found also as micro-inclusions in minerals. The sediments of the horizon “A” are characterized by elevated grades of light rare-earth elements (LREE) over heavy rare-earth elements (HREE). The weathering processes reveal a gradual transition from a moderately warm and humid climate to a cold and dry climate as the placer deposit was formed. The intercalations between horizontal- and crossbedding characterize the conditions of placers’ sedimentation by eluvial, eluvial-alluvial, alluvial-lacustrine and lacustrine environments. U-Pb dating of zircons from the productive horizon “A” of the Karaotkel placer deposit showed a crystallization age of 287 ± 1 Ma. This is identical with the age of the Karaotkel-Preobrazhenka multi-phase igneous intrusion suggesting that it can be considered as the source of the Karaotkel Ti-Zr placer. In addition, comparative analyses of elemental composition of zircons confirmed that monzonites and syenites of earlier phases of the Karaotkel-Preobrazhenka intrusion are the likely source rocks for the Karaotkel mineral sands. The formation of these Ti-Zr placers comprise the following stages: 1) establishment of the bedrock of the Karaotkel-Preobrazhenka multiphase igneous intrusion of the Permian Cisuralian epoch; 2) development of weathering crust during Upper Cretaceous period; 3) washing-out of the weathering crusts during the North Zaysan formation in the Paleogene, and 4) differential redeposition by temporary streams that resulted in the accumulation of Ti and Zr minerals.

Replenishment of mineral resources, especially gold and rare metals, is critical for progress in the mining and metallurgical industry of Eastern Kazakhstan. To substantiate the scientific background for mineral exploration, we study microinclusions in minerals from gold and rare-metal fields, as well as trace-element patterns in ores and their hosts that may mark gold and rare-metal mineralization. The revealed compositions of gold-bearing sulfide ores and a number of typical minerals (magnetite, goethite, arsenopyrite, antimonite, gold and silver) and elements (Fe, Mn, Cu, Pb, Zn, As, and Sb) can serve as exploration guides. The analyzed samples contain rare micrometer lead (alamosite, kentrolite, melanotekite, cotunnite) and nickel (bunsenite, trevorite, gersdorffite) phases and accessory cassiterite, wolframite, scheelite, and microlite. The ores bear native gold (with Ag and Pt impurities) amenable to concentration by gravity and flotation methods. Multistage rare-metal pegmatite mineralization can be predicted from the presence of mineral assemblages including cleavelandite, muscovite, lepidolite, spodumene, pollucite, tantalite, microlite, etc. and such elements as Ta, Nb, Be, Li, Cs, and Sn. Pegmatite veins bear diverse Ta minerals (columbite, tantalite-columbite, manganotantalite, ixiolite, and microlite) that accumulated rare metals late during the evolution of the pegmatite magmatic system. The discovered mineralogical and geochemical criteria are useful for exploration purposes.

We present results of a comparative study of Late Paleozoic granitoids of Eastern Kazakhstan and Western Transbaikalia composing the large Kalba–Narym and Angara–Vitim batholiths. We have established that despite the different geologic history of these regions, granitoid magmatism there proceeded nearly synchronously at the Carboniferous/Permian boundary (330–280 Ma) and was accompanied by mantle magmatism. The regularities of its evolution are considered in terms of the plume model and different stages of interaction of mantle plumes with the lithosphere. The major principles of plume–lithosphere interaction in accretion-collision fold belts have been formulated: (1) Plume-lithosphere interaction results in large-scale melting of sublithospheric mantle, lower lithosphere, and crustal substrates warmed by the preceding orogenic processes; (2) The processes last 30 to 50 Myr and produce large volumes of igneous rocks, mostly granitoids; (3) The sequence of formation of granitoid and basic igneous complexes and the metallogenic specialization can be different and depend on the lithosphere structure and preceding geologic history of the region.

This paper presents a study of ongonites from the Chechek and Akhmirovo dike belts located within the Kalba—Narym batholith in Eastern Kazakhstan. The obtained conclusions are based on the investigations of melt and fluid inclusion in quartz phenocrysts, supplemented by mineralogical and geochemical data. It was established that the dike rocks were formed by crystallization of volatile-rich rare-metal melts in the presence of an aqueous fluid phase with subordinate amounts of carbon dioxide and methane. The ongonites crystallized from three geochemically different melts. Porphyritic phenocrysts in the ongonites of the Chechek and Akhmirovo dike belts crystallized at close temperatures 560–605°C and pressure of 3.6–5.3 kbar. Ongonite magmas that formed the Chechek and Akhmirovo dike belts had a high ore potential. However, degassing dynamics was not favorable for the development of metasomatism and formation of hydrothermal mineralization at the level of dike emplacement. The area of the rare-metal magmatism represented by ongonite dikes and rare-metal granite pegmatites has been distinguished in the northern part of the Kalba—Narym zone. The formation of rare-metal magmas was related to the differentiation in large granitoid chambers under the effect of juvenile fluids derived from the Tarim mantle plume.

The paper presents new geological, mineralogical, and isotope geochronological data for rare-metal pegmatites in the Kalba granitic batholith (Eastern Kazakhstan). Mineralization is especially abundant in the Central-Kalba ore district, where pegmatite bodies occur at the top of large granite plutons and at intersections of deep faults. The pegmatites contain several successive mineral assemblages from barren quartz-microcline and quartz-microcline-albite to Li-Cs-Ta-Nb-Be-Sn-bearing cleavelandite-lepidolite-spodumene. Ar-Ar muscovite and lepidolite ages bracket the metallogenic event between 291 and 286 Ma. The pegmatite mineral deposits formed synchronously with the emplacement of the phase 1 Kalba granites during the evolution of hydrous silicate rare-metal magmas that are produced by the differentiation of granite magma at large sources with possible inputs of F and rare metals with fluids.

Geological and new geochronological data are summarized for the Kalba-Narym granitic batholith in eastern Kazakhstan, and their geodynamic interpretation is suggested. In the structure of the batholith, we consider (from late to early) the Kunush plagiogranitic complex, the Kalguta granodiorite-granitic association, and the Kalba granitic, Monastery leucogranitic, and Kainda granitic complexes. The granitic complexes of the Kalba-Narym batholith were formed between the Carboniferous-Permian and the Early-Middle Permian (∼30 Ma). New data indicate that formation of the Kalba-Narym batholith was related to the activity of the Tarim mantle plume. Heating of the lithosphere by the plume coincided with postcollision collapse of the orogenic structure and led to the crust melting and formation of the studied granitic complexes in a relatively short period.

The results of studies of the Chechek and Akhmirovo dyke belts (the Kalba-Narym zone of Eastern Kazakhstan) constituted by rare-metal Li-F-granitoids (ongonites) are presented. The results of geochemical mapping of dyke belts are given, as are the first-obtained data on the rare-metal composition of rock-forming minerals and melt inclusions. The data on precision dating of rocks by means of the 40Ar/39Ar-isotope technique are presented. It is shown that the dyke belts were formed from the melts of three different geochemical types. The existence of these types might be caused by differentiation within the deep-seated magma chambers. The data of geochronology permit us to conclude that the centers of rare-metal Li-F-magmatism characteristic of the large magma provinces that appeared under the impact of mantle plumes on the arisen continental crust might have been formed at the final stages of the formation of the Kalba-Narym batholith. This allows one to assume the rare-metal Li-F-granitoids (ongonites) of the dyke belts in Eastern Kazakhstan belong to the large Late-Paleozoic magma province that appeared in the region of Central Asia as a result of the activity of the Tarim plume.

New data of petrography, mineralogy, and geochemistry from the Irtysh shear zone in Eastern Kazakhstan reveal three types of gabbro: (1) dolerite and gabbrodolerite, (2) biotite-bearing gabbronorite and gabbrodiorite, and (3) layered peridotite-gabbro intrusions. Rocks of types 1 and 2 occur mainly as small bodies and share similarity in major- and trace-element compositions. Layered gabbro (type 3) forms the largest intrusion in the area and has a different composition: higher CaO and Al2O3 but lower K2O, TiO2, P2O5, Zr, Nb, REE. Correspondingly, the gabbro of two first types may result from differentiation of the same tholeiite magma, whereas the layered gabbro rather derived from a magma intermediate between tholeiite and calc-alkaline series. According to geochemical and isotopic signatures, both types of primary magma originated from the same sublithospheric depleted mantle by low- and high-degree partial melting of spinel lherzolite. The obtained 317–313 Ma U-Pb and Ar-Ar ages of the gabbro fall within the time of collisional events in the area. The suggested model explains the origin of syncollisional gabbro as intrusion of ascending mafic melts from a mantle wedge at the transform boundary of colliding plates along the Irtysh shear zone where strike-slip faulting produced slab windows open to inputs of hot asthenospheric material.

Early Caledonides in the Olkhon region of western Cisbaikalia, being part of the folded framing of the Siberian craton, are a unique geologic object for studying processes of mantle–crust interaction at deep levels of the Earth’s crust. This paper describes restitic ultramafic bodies and boudins spatially confined to faults (blastomylonite sutures), as well as synkinematic granites related to amphibolite facies of metamorphism. Estimates are given for the PT-conditions of metamorphic rocks from the folded framing of the ultramafic bodies, the chemical and mineral compositions of ultramafic rocks, blastomylonites and synkinematic granites, and the results of U–Pb and Ar–Ar isotopic dating. Particular attention is paid to the thermal history of tectonic exposure of the ultramafic bodies as relics of the paleo-oceanic crust in the Early Caledonian collisional system of western Cisbaikalia.

One of the problems faced by researchers when paleogeodynamic reconstructions are carried out for deeply eroded orogenic terranes is the limited usage of geological and isotopic geochemical data on volcanic associations. The utilization of information on gabbroids and granitoids considered separately also fails to resolve this problem. The convergence of features of arc, collisional, and within-plate magmatic processes leads the researcher to search for indicator plutonic associations, such as paired gabbrogranite intrusive series. The latter were distinguished using geoinformation databases (including those compiled by the authors of this paper), which were composed for the Early Caledonides in the Altai-Sayan folded area and adjacent territories. This makes it possible to characterize mantle-crustal magmatism in suprasubductional and collisional environments and the conditions under which these geodynamic regimes (plate- and plume-tectonic factors) interact. This paper presents estimates of the composition of the parental basic magmas, distinctive features of their differentiation, and the compositional specifics of the accompanying extensive granite-forming processes. The example of the Altai-Sayan folded area and adjacent territories is employed to correlate the composition of the basic-ultrabasic and granitoid magmas and, on this basis, distinguish (a) differentiated gabbro-tonalite-plagiogranite intrusive series corresponding to accretionary-collisional geodynamic environments, and (b) gabbro-monzonite-granosyenite-potassic granite intrusive series, which were produced when the accretionary-collisional system was affected by a plume.

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.

Based on the first isotopic geochronological data obtained by the classic U–Pb method by zircons [1–3], it was established that magmatic and metamorphic rocks of the Ol’khon region are of Early Paleozoic age. The age of granulite metamorphism of the Chernor� udskaya zone rocks spreading as a narrow band (with a width of

Structural-petrologic and isotopic-geochronologic data on magmatic, metamorphic, and metasomatic rocks from the Chernorud zone were used to reproduce the multistage history of their exhumation to upper crustal levels. The process is subdivided into four discrete stages, which corresponded to metamorphism to the granulite facies (500–490 Ma), metamorphism to the amphibolite facies (470–460 Ma), metamorphism to at least the epidote-amphibolite facies (440–430 Ma), and postmetamorphic events (410–400 Ma). The earliest two stages likely corresponded to the tectonic stacking of the backarc basin in response to the collision of the Siberian continent with the Eravninskaya island arc or the Barguzin microcontinent, a process that ended with the extensive generation of synmetamorphic granites. During the third and fourth stages, the granulites of the Chernorud nappe were successively exposed during intense tectonic motions along large deformation zones (Primorskii fault, collision lineament, and Orso Complex).

The problem of identifying igneous complexes related to mantle plumes that exist independently from upper mantle processes remains topical at present. The data on magmatism of “hot spots” and “hot fields” localized in both oceanic and continental geological structures, which were obtained over the last 15–20 years, indicate that the geochemical and isotopic methods traditionally used for identifying products of plume magmatism appear to be ineffective in some situations. This is explained by convergence between geochemical and isotopic characteristics of mantle rocks characterized by elevated alkalinity from different tectonic settings, on the one hand, and, to a large extent, heterogeneity of mantle sources generat� ing magmas with “intraplate” properties, on the other. It is clear now that along with autonomous “Morgan� type” lower mantle plumes, there are also the “Ander�

The Ol’khon region represents a fragment of the West Baikal collision belt that resulted from Early Caledonian accretionary‐collisional processes related to the closure of the Paleo-Asian ocean in the southern margin (in present-day coordinates) of the Siberian Craton [1‐3]. This communication is dedicated to analysis of the internal structure and age of protoliths from this region based on U‐Pb dating and the Sm‐Md isotopic composition of igneous complexes. The U‐Pb (SHRIMP-II) age of rocks was measured at the Center of Isotopic Studies (VSEGEI, St. Petersburg) using the technique described in [4]. The Sm‐Nd isotope composition of bulk rock samples was determined by the standard method [5] at the Laboratory of Isotope Geochronology and Geochemistry (Geological Institute, Kola Scientific Center, Russian Academy of Sciences, Apatity). Figures 1 and 2 demonstrate experimental results obtained for two periods (500‐485 and 475‐465 Ma ago) (Figs. 1, 2), which reflect the scale and spatial distribution of synmetamorphic and intrusive igneous rocks in the southwestern part of the Ol’khon region. 1

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.

We present petrological, isotopic, and geochronological data on gabbro-picrite plutons from the Altai collisional system of Hercynides (eastern Kazakhstan). The geological, geochemical, and geochronological data suggest that these rocks are indicators of the activity of the Tarim plume. The gabbro and picrites formed in two stages (~293 and 280 Ma) in an acid-to-basic succession, explained by a model for the interaction of thermochemical plumes with the lithosphere. Early igneous activity, which gave rise to subalkalic gabbro plutons, reflects the first interaction between the ascending plume and the lithosphere, with low-melting sublithospheric protoliths. Further interaction was characterized by the sublithospheric spread of the plume head with intense heating of the lithospheric base and possible intrusion of deep melts, which resulted in the formation of Cu–Ni–PGE gabbro-picrite plutons in the Altai collisional system and Northwest China.