In 1720, the Russian Tsar Peter the Great mounted the first expedition to Siberia to identify and explore natural resources. Later, the Academy of Sciences undertook later several expeditions. The intensive development of ore reserves began in the 19th century, with the focus being on the territories of Altai and Transbaikalia. The Russian Geological Committee was established in 1882 for the purpose of compilation of the geological map of Russia and systematic study of Siberia's territory. At the end of the 19th century, a university and a technological institute were established in Tomsk. These became the first education institutions, which had a great influence on the development of geological perceptions and exploration in Siberia. The post-revolution period marks the beginning of industrialization in Russia, which highlighted the need for the exploration of more natural resources. This accelerated the advance of geological survey and exploration work. This period witnessed the discovery and exploitation of hundreds of mineral deposits, e.g., coal and iron ore deposits in the Kuznetsk Basin, copper-nickel ore deposits in the Norilsk region, gold and polymetallic deposits in Transbaikalia, etc. The research and exploration activities ceased during the Great Patriotic War, and geologists were mobilized to help the front. Immediately after the war, they again became actively involved in the restoration of the country's economy. In the 1950s, exploration geologists achieved remarkable results, e.g., the discovery of large-size oil and gas fields in West Siberia and diamond deposits in Yakutia. The Siberian Branch of the Academy of Sciences and the Institute of Geology and Geophysics as its part were established in 1957. A number of geological research institutes were also created in Irkutsk and Yakutsk. Basic geological research made an important contribution to unlocking the resource potential of Siberia.

Studies of the geological history of the Yenisei Ridge are important not only for understanding the tectonic evolution of mobile belts at the boundaries of ancient cratons but also for problem solving whether the Siberian craton was a part of the Rodinia supercontinent. The mineralogical-petrological, geochemical and isotope-geochronological studies yielded new data on the petrogeochemical composition, petrogenesis features, U-Pb age of zircon, and Sr and 147Sm-143Nd isotopic parameters for the rocks of the Ryazanovsky granitoid massif located near the Yenisei fault zone of the Yenisei Ridge. These rocks are represented by high-ferruginous peraluminous varieties and are comparable to A-granites or highly differentiated I-granites. Their composition evolves from normal to subalkaline granites and leucogranites, characterized by increased concentrations of highly charged and radioactive elements. Isotopic (Sr, Nd) characteristics of the rocks indicate generation from an ancient crustal substrate, the average age of which corresponds to the Paleoproterozoic. The formation of these granites at the Meso-Neoproterozoic boundary (1013±9.9 Ma) corresponds to the early stage of the Grenville orogeny and the formation time of the structure of the Rodinia supercontinent. This episode of regional crustal evolution is correlated with the synchronous successions and similar style of tectonothermal events on the periphery of large Precambrian cratons (Laurentia and Baltica), thus confirming the reliability of the proposed paleocontinental reconstructions of incorporation of the Siberian craton into the Rodinia.

As a large gold-bearing province, the Yenisei Ridge does not show elevated background gold concentrations. All types of its sedimentary, metamorphic, and igneous rocks, except only the carbonaceous black shales, contain concentrations of the noble metal at the level of its Clarke values. All local gold deposits are constrained within the regional Central Metallogenic Belt, in which geological–geochemical conditions occurred that were favorable for the deposition of gold and gold–uranium ore mineralization: most of the deposits are constrained within a trough structure, the area was affected by several pulses of plume magmatism, which introduced, redistributed, and concentrated gold and uranium, and the developing ore-concentrating and ore-controlling systems formed economic deposits and associated zones of hydrothermal metamorphism with geochemical aureoles of Pb, Zn, Ag, Au, Bi, and As.

Based on the proposed numerical model of the stress-strain state of polymineral rocks, which describes the formation of blastomylonites in the Yenisei Regional Shear Zone (PRSZ) in the Yenisei Ridge, the possibility of local tectonic overpressure exceeding the lithostatic pressure in rocks subjected to shear deformations is shown. For tectonites of the southern (Angara-Kan block) and northern (Isakovka terrane and Garevka complex) segments of the PRSZ, estimates of the maximum overpressure were obtained from 2–3 to 4–5 kbar, which range from 25 to 50% of the lithostatic pressure. It is shown that excess pressures can be preserved in a local volume on a geological time scale sufficient for their fixation in metamorphic minerals. Model values of overlithostatic pressure in garnet-amphibole tectonites and geobarometric estimates of peak values during stress metamorphism allow us to offer new evidence of pressure inhomogeneity in natural mineral associations. Using the results of numerical modeling for the evolution of fault metabasite blastomylonites, it was established that the overpressure at the stage of syn-deformation metamorphism in the shear zone are possible at temperatures up to 600–650°C and not reaching 800°C; the presence of fluid or partial melt prevents the occurrence of overpressure. The amount of excess pressure due to shear stresses depends on the mineral composition and structure of the rock.

It is established for the first time that biotite plagiogneisses from the Garevka metamorphic complex of the North Yenisei Ridge have geochemical characteristics of C-type adakites with island-arc melt sources. The Hf isotopic composition of zircons indicates the participation of several sources in the formation of the granite melt, including the juvenile mantle and older crustal rock protoliths with model ages THf(DM)с = 1838–1916 and 1965–2357 Ma, respectively. Based on the results of U–Pb dating of zircons, new pulses of Neoproterozoic endogenous activity at the western margin of the Siberian Craton (913 ± 11 and 915 ± 36 Ma for adakite-like granites and 932 ± 26 Ma for leucogranites), correlating with the Grenville tectonic events, were determined. These Grenville episodes of regional crustal evolution are correlated with the synchronous successions and a similar style of tectonothermal events along the Arctic margin of the supercontinent Rodinia. This confirms the spatial proximity of Siberia and the North Atlantic cratons (Laurentia and Baltica), which is consistent with the proposed Neoproterozoic paleogeographic reconstructions of Rodinia.

Fe- and Al-rich metapelite from the Transangarian segment of the Yenisey Ridge (East Siberia, Russia) is a potential new source of high-alumina refractories. The rocks have relatively high average contents of Al2O3 (20 wt%) and Fe2O3 (7.91 wt%), moderate K2O (3.44 wt%), and low CaO (0.74 wt%). Their dominant mineral assemblages are andalusite + muscovite + margarite + chlorite + biotite + quartz or staurolite + kyanite or/and andalusite + chlorite + muscovite + biotite + quartz with ±garnet and ±plagioclase. Al2SiO5 polymorphs occur as up to 1.5 cm andalusite porphyroblasts and partial or complete pseudomorphs after andalusite (kyanite and staurolite). Accessories include abundant Fe–Ti oxides and sporadic REE-, Y-, Ca-phosphates; sulfides are negligible. The composition of Al2SiO5 concentrates obtained in laboratory by heavy-media and magnetic separation from ≥0.06 mm fractions meet all requirements for raw material of this type: >56 wt% Al2O3, <42 wt% SiO2, <1 wt% Fe2O3, <1.2 wt% TiO2, and <0.2 wt% (CaO + MgO). The andalusite, kyanite, and mixed ores yield 0.7–4.1 wt%, 0.7–2.2 wt%, and 1.9–6.0 wt% of concentrate, respectively. The best-quality ores rich in Al2SiO5 polymorphs reside in zones of contact and/or dynamic metamorphism superimposed over regional metamorphism of Al-rich rocks.

— The paper provides evidence that collisional magmatism related to the Neoproterozoic (880−860 Ma) orogenic event occurred in the southwest of the Siberian Craton. Newly obtained data are presented on the major-component and trace-element composition, U−Pb (SHRIMP II) zircon age, and Sm−Nd isotope composition for rocks of the Gusyanka granitoid massif in the Yenisei fault zone of the Yenisei Ridge. The concordant U−Pb zircon age of the Gusyanka massif is 871 ± 11 Ma indicates that its rocks were formed in the mid-Early Neoproterozoic, simultaneously with the rocks of the Kalama and Eruda massifs in the Tatarka−Ishimba fault system, during the same stage of the collisional events at approximately 880–860 Ma. The calc-alkaline granites, granodiorites, and leucogranites of the Gusyanka massif are classified, on the basis of their high alumina content and trace element composition, as S-type and were derived from a metapelitic source. Many trace-element parameters of rocks of the Kalama and Eruda massifs correspond to those of low-potassium I-type granites, which were most likely derived from mafic rocks and tonalites. The granitoids of the Gusyanka massif, on the one hand, and the Kalama and Middle Tyrada massifs, on the other, differ contrastingly in Nd isotope composition. The source of the former was either metapelites of the Tungusik Group or metasedimentary rocks of the Sukhoi Pit Group, with the involvement of juvenile material. The melts of granites of the Kalama and Middle Tyrada massifs might have been derived from a source with the involvement of an older, possibly Paleoproterozoic, crustal material and a juvenile mafic source. Thus, the orogenic events at 880−860 Ma led to the generation of melts at different levels of the Paleo- to Mesoproterozoic crust of the trans-Angara region of the Yenisei Ridge. The geodynamic history of the region is correlated with the synchronous successions and similar style of tectono-thermal events along the peripheries of the large Precambrian cratons of Laurentia and Baltica, and this is consistent with paleocontinental reconstructions of the close spatiotemporal relations between these cratons, Siberia, and their incorporation into Rodinia.

Research subject. Аndalusite- and kyanite-bearing (13–19 wt % Al2SiO5) rocks of the Teya metamorphic complex (Mayakon and Panimba areas), Yenisei Ridge. Aim. To study the composition and mineral content of high-alumina rocks from the Panimba and Mayakon areas. Materials and methods. Laboratory mineral processing was employed to estimate the mineral content of metamorphic rocks of the Teya complex using a magnetic and gravity separation at the Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The concentrates were obtained from typical samples of andalusite, kyanite, and andalusite-kyanite metapilites. After crushing and grinding, the rock samples were separated into size fractions <0.06, 0.06 ≤ x < 0.1 and 0.1 ≤ x < 0.25 mm. The concentrates were recovered from size fractions ≥0.06 mm. Phase, bulk rock, and trace element composition of the rock samples, mineral concentrates, and other fractions were analyzed using XRD, XRF, ICP-MS, and SEM. Results. The magnetic product obtained at the first stage of mineral processing using magnetic separation accumalated staurolite, biotite, chlorite, ilmenite, pyrrhotite, and pyrite. At the second stage, light products containing quartz, feldspars, and muscovite were separated from non-magnetic products with CHBr3 using a centrifugal concentrator. At the last stage, using a double-knife separator, the heavy product from the previous beneficiation stage was separated into a “magnetic” raw concentrate (52–92 wt % Al2SiO5) and a “non-magnetic” final (70–97 wt % Al2SiO5) concentrate. The andalusite-kyanite concentrates (up to 97 wt % Al2SiO5) were obtained by the combination of cheapest and simplest methods of magnetic and gravity separation. The concentrates containing andalusite and kyanite with low recovery (0.7–6%) are comparable to the grade of kyanite-bearing ores of Karelia, the Kola Peninsula, and Gansu Province, China. Conclusions. The study shows that high-quality andalusite and/or kyanite concentrates can be recovered from high-alumina metapelites of the Teya metamorphic complex.

The unusual composition of the protolith, its structural and textural heterogeneity, limited mass transfer and high temperatures are the causes of rare mineral formation and mineral associations during metamorphism and metasomatism. Most often, this is observed in shallow conditions (pressure up to 3 kbar) when additional heat is supplied to the rocks by magmatic intrusions. In the article, these issues are discussed on a number of geological complexes, in which the manifestations of metamorphism with the development of rare minerals and mineral associations have been studied in detail.

The reasons for the formation of rare minerals and mineral assemblages during metamorphism and metasomatosis are found to be the atypical composition of the protolith, the structural–textural heterogeneity, restricted mass transfer, and high temperatures. This is often observed under shallow conditions (pressure up to 3 kbar) during additional heating of rocks by igneous intrusions. In this paper, these questions are discussed with a series of domestic examples, the processes of mineral formation in which are studied in detail.

The results of a study of the Precambrian rocks of the Yenisei Ridge to identify gold contents in them are presented. It is shown that in all types of sedimentary, metamorphic and igneous rocks, with the exception of black carbonaceous shales, the concentration of the noble metal is at the level of its Clarke values the average abundance in these rocks. The maximum gold content (from 10-20 to 60 mg/t) was found in the black carbonaceous shales of the Teya and Sukhoi Pit groups, Rybinskaya and Panimba sequences. Gold ore bodies of deposits are confined to numerous horizons of carbonaceous shales. The data obtained show that the Yenisei Ridge, as a large gold-bearing province, is not distinguished by an increased background in Au. All gold deposits are concentrated within a single Central metallogenic belt, in which there are favorable geological and geochemical prerequisites for the formation of gold and gold-uranium mineralization. The most important of them are: the location of deposits between the Tatarsky and Ishimba deep faults in the trough structure of the Rybinsk-Panimba volcanic belt with an increased Au content in basic rocks, picritoids, carbonaceous shales; increased Au contents in black carbonaceous shales at different stratigraphic levels of the Teya and Sukhoi Pit Proterozoic groups, U and Th in granite-gneiss domes, Na-K rhyolites, and subalkaline granites; manifestation of potassium-sodium granitoid (850 Ma ago), intraplate, riftogenic plume magmatism at the level of 780, 750, 700 and 650 Ma, which led to the input, redistribution and concentration of gold and uranium; development of ore- forming and ore-concentrating systems that form economically significant deposits, accompanied by zones of hydrothermal metamorphism and geochemical aureoles of Pb, Zn, Ag, Au, Bi and As, identified using modern methods of analysis of matter.

The tectonic evolution of the Siberian cratonic margins offers important clues for global paleogeographic reconstructions, particularly with regard to the complex geological history of Central Asia. The Yenisey Ridge fold-and-thrust belt at the western margin of the Siberian Craton forms part of the Central Asian Orogenic Belt (CAOB) and is a key to understand the Precambrian tectonic evolution of the Siberian Craton and crustal growth in the CAOB. Understanding the tectonic evolution of the Yenisei Ridge is crucial for solving the debate related to the role of the Siberian Craton within the Rodinia supercontinent assemblies and breakup with the opening of the Paleoasian ocean. Here we report new data on the petrogenesis, tectonic settings, thermodynamic conditions, metamorphism and protolith ages for compositionally contrasting rocks of the Garevka metamorphic complex, obtained from the results of mineralogical-petrological, geochemical, and isotope-geochronological studies. Possible models and geodynamic settings for their formation are discussed. Based on the results of U-Pb dating of zircons, two new pulses of Neoproterozoic endogenous activity at the western margin of the Siberian craton were established, associated with Grenville (930–900 Ma) and (880–845 Ma) post-Grenville Valhalla (880–845 Ma) accretion-and-collision processes. These episodes of regional crustal evolution are correlated with the synchronous successions and similar style of rocks along the Arctic margin of Rodinia and supports the spatial proximity of Siberia and North Atlantic cratons (Laurentia and Baltica), which is consistent with the proposed Neoproterozoic paleogeographic reconstructions of the Rodinia configuration.

The relevance of the research is due to fundamental and applied aspects. The polymorphic modifications of Al2SiO5, namely kyanite, andalusite, and sillimanite - minerals of sillimanite group (MSG), are among the most important indicators of metamorphism in pelitic lithologies. The "triple point" corresponding to the equilibrium coexistence of all polymorphs Al2SiO5 is one of the most important invariant point in metamorphic petrology, and mineral associations with the participation of "triple point" polymorphs are informative for calibration of geothermobarometers. On the other hand, the Al2SiO5 polymorphs (andalusite, kyanite, and sillimanite), which are dominant constituents in aluminous metamorphic rocks of the North Yenisei Ridge, are gaining increasing importance as industrial sources for aluminum oxide, silumin, and aluminum. The polymetamorphic history of a series of metamorphic complexes of Al-rich metapelites in the Yenisei Range, with rocks containing the Al silicate triple-point assemblage (all three Al2SiO5 polymorphs) is illustrated by geologica-structural, mineralogical-petrological, and isotope geochronological evidence. In the studied aureoles, the overprinting of earlier mineral assemblages with the later ones during various geodynamic events obviously follows from the reaction microtextures and chemical zoning in minerals, the.-T trajectories of these rocks, as well as radiometric dating. These indicator features show that the Al2SiO5 polymorphs sequentially grew as a result of a complex polymetamorphic history due to the changes in the tectonic settings. In the Teya metamorphic complex, areas of development of metapelites of andalusite-sillimanite regional metamorphism have been established, within which the promising Panimba andalusite and Teya sillimanite deposits are concentrated. Products of the superimposed kyanite-sillimanite type of metamorphism in the thrust zone form a number of bimineral (andalusitekyanite) (Mayakon, Chirimba, etc.) and polymineral (andalusite-kyanite-sillimanite) (Vorogovo, Lower Veduga, Nerazgadannoe occurrences, etc.) Analysis of the resource base of alumina-containing minerals in the region shows that a number of promising for high-alumina schists (HAS) objects have been discovered in the North Yenisei Ridge, the formation of which is genetically related to tectonic-metamorphic processes of the Grenville and Baikal orogeny. Their constituent MSG, as well as HAS containing staurolite and chloritoid, have sufficient resources for their use in industry together with the explored deposits of bauxite, alumina iron ores, and nepheline syenites.

The Fe- and Al-rich metapelites of the North Yenisei Ridge are redeposited and metamorphosed products of Precambrian kaolinite-type weathering crusts of predominantly kaolinite–illite–montmorillonite–quartz composition. The petro- and geochemical characteristics of the metapelites studied are mainly due to the features of sedimentation during the formation of the protolith, which could have been formed due to erosion of the Lower Proterozoic microgneisses (1962–2043 Ma) of the Siberian Сraton with the involvement of an admixture of mafic and felsic rocks into the provenance area and subsequent accumulation in marginal continental shallow basins under humid climate conditions and a calm tectonic regime. The data obtained on the nature and composition of the protolith of these rocks are consistent with data of lithofacies analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the North Yenisei Ridge.

The tectonic evolution of the Siberian Cratonic margins offers important clues for global paleogeographic reconstructions, particularly with regard to the complex geological history of Central Asia and Precambrian supercontinents Columbia/Nuna and Rodinia and its subsequent breakup with the opening of the Paleo-Asian Ocean. Here, we present an overview of geochemical, petrological, and geochronological data from a suite of various rocks to clarify the age, tectonic settings, and nature of their protolith, with an emphasis on understanding the tectonic history of the Yenisey Ridge fold-and-thrust belt at the western margin of the Siberian Craton. These pre-Grenville, Grenville, and post-Grenville episodes of regional crustal evolution are correlated with the synchronous successions and similar style of rocks along the Arctic margin of Nuna-Columbia and Rodinia and support the possible spatial proximity of Siberia and North Atlantic cratons (Laurentia and Baltica) over a long period ~1.4–0.55 Ga.

Research subject. Fe- and Al-rich metapelites of the Teya, Garevka and Angara complexes of the North Yenisei Ridge (western margin of the Siberian craton) were studied. Research methods. Recently-obtained geochronologic (SHRIMP II U-Pb zircon dating) and geochemical data on the distribution of major and trace elements were used to reproduce the composition and age of the protolith, along with the paleofacies formation conditions. Results. The ferruginous-aluminous metapelites of the North Yenisei Ridge consitute redeposited and metamorphosed products of Precambrian weathering crusts predominantly of the kaolinite rather than lateritic type, as was previously thought. The chemical weathering of rocks in the Early Proterozoic on the Yenisei Ridge did not reach the deep stage of lateritization with the formation of zones of final decomposition of aluminosilicates; however, this process was limited to the formation of weathering products of predominantly kaolinite-illite-montmorillonite-quartz composition. Conclusions. The petro- and geochemical characteristics of the studied metapelites are mainly due to the features of sedimentation during the formation of the protolith, which could have been formed due to the erosion of the Lower Proterozoic microgneisses of the Siberian craton with ages in the range of 1962-2043 Ma with the involvement of granitoid and volcanic admixture of mafic rocks into the erosion area and subsequent accumulation in marginal continental shallow basins under the conditions of a humid climate and a calm tectonic regime. These results are consistent with the data of lithofacies analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the North Yenisei Ridge.

The geological position, U-Pb monazite age, and composition of charnockites from the central part of the Anabar shield are presented. The charnockites are localized in a block of the Paleoproterozoic metasedimentary granulite-facies rocks, which include aluminous schists, sapphirine-bearing schists, and hypersthene plagiogneisses typical of the Archean Daldyn granulite complex. Moderate-K charnockites form small pockets and lenses in the hypersthene plagiogneisses, inherit their gneissic appearance, and are related with them by gradual transitions. High-K charnockites compose large vein bodies with cutting contacts. The charnockites differ in the structural position, but have similar age (1982 Ma) and are separated in time from metasedimentary rocks, whose age is estimated at 2.4–2.5 Ga. Hypersthene plagiogneisses correspond to igneous rocks of predominantly intermediate composition, while charnockites are granodiorites and granites. Compared to the plagiogneisses, charnockites are enriched in Th, light REE, Zr, Nb, Rb, and Ba. Hypersthene plagiogneisses and charnockites are characterized by a highly fractionated REE distribution pattern with an increase in (La/Yb)n and Eu minimum in charnockites. According to geochemical data and close Nd isotopic composition, high-K charnockites could have been generated during the high-temperature melting of hypersthene plagiogneisses. Charnockites (~2.0 Ga) are almost coeval to the Paleoproterozoic granulite metamorphism and emplacement of granite intrusion in collision zones. All these processes are caused by the accretion of Early Precambrian terranes into the structure of the Siberian craton. Charnockitization was superimposed on the hypersthene plagiogneisses, which have been already deformed in folds and migmatized, and on the metasedimentary sequence. This process completes the formation of the granulite complex of the Anabar Shield.

The Al2SiO5 polymorphs (andalusite, kyanite, and sillimanite), which are widespread in aluminous metamorphic rocks, gain increasing importance as industrial sources for producing aluminum oxide, silumin, and aluminum. The polymetamorphic history of a series of metamorphic complexes of Al-rich metapelites in the Yenisei Range, with rocks containing the Al silicate triple-point assemblage (all three Al2SiO5 polymorphs) is illustrated by geological–structural, mineralogical–petrological, and isotope geochronological evidence. In the studied aureoles, the overprinting of earlier mineral assemblages with the later ones during various geodynamic events obviously follows from the reaction microtextures and chemical zoning in minerals, the Р–T trajectories of these rocks, as well as radiometric dating. These indicator features show that the Al2SiO5 polymorphs sequentially grew as a result of a complex polymetamorphic history due to the changes in the tectonic settings. A comparative analysis of the results and literature data on other metamorphic regions worldwide shows that the Al2SiO5 minerals always (at least in the studied rocks) occur in reaction relationships with one another, grew at different time periods during the metamorphic history of the rocks, and hence, cannot be regarded as true triple-point assemblages, although some segments of the looping P–T paths may pass near the triple point. We conclude that the aluminum silicate triple-point assemblages, in which all three Al2SiO5 minerals are in stable equilibrium, are not possible in metapelitic rocks of any chemical composition. Hence, such purported triple-point assemblages cannot represent a stable association and cannot be used to calibrate or test geothermobarometers.

Metapelites and metabasites within the Yenisei regional shear zone of the Yenisei Ridge underwent strong deformations with substrate recrystallization and blastomylonite formation during the Ediacaran. The geostructural, petrological, and isotopic–geochronological characteristics of development of the Late Neoproterozoic blastomylonite complexes marking the junction zone of the paleocontinental and paleoceanic sectors of the Yenisei Ridge have been analyzed. Two zones of heterogeneous blastomylonite complexes have been recognized from west to east, in order of increasing distance from the paleoceanic structures: (I) high-baric complexes of the suture zone and (II) frontal (above-suture) medium-baric and medium- to low-temperature complexes. The established differences in the Р–Т parameters of metamorphism between strongly and weakly deformed rocks were interpreted using well-known geodynamic models based on different tectonic mechanisms. As a result of the analysis, we found that the polychronous dynamic metamorphism of gneisses of the Angara–Kan block in the south and formation of the bulk of blastomylonites in the northern segment of the shear zone in the Northern Yenisei Ridge occurred with a 1.5–3 kbar increase in pressure along with insignificant increase in temperature and low metamorphic gradient dT/dH < 10°C/km compared to the background values of earlier regional metamorphism. This was probably due to crustal thickening as a result of rapid thrusting/subduction, followed by rapid uplift. The maximum excess values of the thermodynamic parameters of metamorphism were established in apometabasite tectonites of the suture zone with relict glaucophane schist associations that underwent metamorphism with a simultaneous significant increase in pressure by 3–5 kbar and temperature by 180–240°C with a higher dT/dH gradient of 15–20°C/km. Such excess Р–Т values could be due to progressive metamorphism, complicated by local heating of rocks during viscous deformations and excess oriented tectonic pressure over lithostatic in ductile shear zones. The data agree well with the results of numerical experiments, and this confirms the role of tectonic stress as an additional thermodynamic factor of metamorphic alterations in crustal suture zones.