The eclogite-blueschists Maksyutov Complex is characterized by a complex fold-and-thrust structure that was developed during the Late Devonian collision between Baltica (East European Plate) and the Magnitogorsk Arc, that was formed during the Early Devonian intraoceanic subduction. Eclogites are the most studied rocks of the complex; their formation and exhumation are usually associated with the collisional stage of orogen development. At the same time, the origin of meta-ultramafic rocks, which together with eclogites form sheeted and lenses within metasedimentary rocks (shales and quartzites), still remains unknown. This paper presents the results of the first detailed petrological study of meta-ultramafic rocks, represented by antigorite-chlorite and magnesite-antigorite metaharzburgites, chlorite-antigorite metaorthopyroxenite. Mineral compositions and textural relationships between minerals in metaharzburgites indicate at least two stages of rock transformations. Minerals of the early mineral paragenesis (first stage) – olivine, accessory chromite and low-fluorine Ti-clinohumite – have a metamorphic genesis; ultrahigh-pressure (UHP) conditions of their formation are discussed. At the second stage, there was a partial replacement of olivine by orthopyroxene-bearing parageneses with Cr-Al antigorite and/or high-chromium chlorite. Based on the phase equilibria modeling using the Perple_X software package, it was found that the formation of antigorite-orthopyroxene paragenesis was associated with Si-Al metasomatism at: T ~ 630°С, P ~ 2 GPa, logaSiO₂~ –0.6, logaAl₂O₃~ – 2.5. It is important to note that the mineral paragenesis are highly sensitive to aSiO₂: a slight decrease in lgaSiO2 relative to the above value would lead to the growth of olivine with antigorite, and an increase would lead to the growth of orthopyroxene. The latter may explain the formation of meta-orthopyroxenites, which are widely distributed among the meta-ultramafic rocks of the Maksyutov Complex. Similar calculations performed for the range of XCO₂= 0.01–0.05 in H₂O-CO₂fluid showed replacing silicate minerals by magnesite under the established thermodynamic conditions. Carbonation and Si-Al metasomatism are specific features of high-pressure transformations of meta-ultramafic rocks, which have not been established in the associated eclogites, quartzites, and shales. Such selectivity of fluid influence on different rock types is interpreted as a result their different tectono-metamorphic evolution: meta-ultramafic rocks are fragments of the suprasubduction mantle, which were tectonically combined with the rocks of the subducting plate (eclogites and metasedimentary rocks).

Research subject. This article presents mineralogical, petrological and geochemical studies of lawsonite eclogites and metasomatites of the Utarbayev Аssociation of the Maksyutov complex. The Utarbayev Association forms an independent unit in the Maksyutovsky complex accretion structure. This Association features a variety of lawsonite-bearing metasomatites that form zonal halos in the frame of block-like diopside-grossular bodies included in the antigorite-serpentinite melange. The Utarbayev Association differs from typical lawsonite-blue shale complexes of collisional oro genes by the absence of mineral parageneses of lawsonite-bearing rocks of blue amphibolites.Methods. A microprobe analysis of the mineral composition was performed using a Cameca SX-100 microanalyzer. The content of petrogenic, rare and rare-earth elements was determined by X-ray spectroscopy (CPM-18) and mass spectroscopy (ICP-MS, ELAN-90). Results. An indicator mine ral paragenesis (Grt + Omp + Lws + Di) ± (Coe-Qz + Ttn) that characterizes lawsonite eclogite was found. Omphacite (Jd38–44) and unchanged lawsonite (Н2O-OH – 11.8%, Ca/Al = 0.48–0.51 и Fe/Al = 0.01 0.02%) are represented as inclusions in grossular-almandine garnet (Alm39–46Grs41–51), coesite – as microinclusions in omphacite. Thermobarometry (Grt-Omp, Grt-Omp-Ph) showed the following formation conditions of lawsonite paragenesis: T = 495–622°C under P = 2.2–2.4 GPa. The age of crystallization of lawsonite eclogite was found to be Lower Paleozoic (471–444 Ma).Conclusions. The lawsonite eclogite of the Utarbayev Association is similar to the complexes of «cold» eclogites, which are formed under the conditions of a very low geothermal gradient and are rarely preserved when removed into the upper crust. The latest review published in the «Journal of Metamorphic Geology» (2014) mentions 19 sites, where lawsonite eclogites were discovered on the earth’s surface. Тhe HP-UHP lawsonitebearing Utarbayev Rock Association complements this list.

Research subject.U-Pb zircon dating, as well as a petrological and geochemical study of pyroxene-amphibole-, pyroxeneamphibole- biotite- and biotite-bearing fenites from the Central Alkaline Band Ilmeno-Vishnevogorsky Complex.Methods.The age of zircons was determined by an ion mass spectrometer (SHRIMP II, Centre of Isotopic Research VSEGEI). The content of REE and trace elements was estimated by secondary ion mass spectrometer methods (CAMECA IMS-4F, Valiev Institute of Physics and Technology RAS).Results.The mineralogical and geochemical (U, Th, REE) features of zircons, as well as fenites, reflect their polygenic-polychronous nature. Most zircon crystals have a metastable matrix and are characterized by averaged REE contents between igneous and hydrothermal types. These crystals are distinguished from magmatic zircons by high LREE contents and low values of Ce anomalies, and from hydrothermal zircons – by differentiated REE distribution spectra. Three ages of zircon were established: 2066–1686 (PR1), 425–404 (S2) and 284–266 (P1) Ma. PR1 zircons reflect the primary features and the degree of changes in the fenite substrate. S2 zircons, limited only to the biotite- bearing fenite, correspond to the age of the miaskite formation process. The P1 zircons clearly reflect the metasomatic process of fenitization initiated by late shear deformations. The temperature of the phenitization processes (based on the Ti content in zircons) was estimated at 630–670°C for S2and ≤ 600°C for P1fenites, respectively.Conclusions.Central Alkaline Band fenites were formed by the metasomatic process of PR1 substrate fenitization in the late stage (P1) of shear strains, which are widely expressed in the Ilmeno-Vishnevogorsky Complex.

The paper presents the main results of isotopic-geochronological and mineralogical-geochemical studies at the territory of the Ilmeny State Reserve over 2010–2020. A summarized age scheme is given for various rock types of the Ilmenogorsk polymetamorphic complex. The textural-structural features of milonites and main directions of metasomatic processes in the rocks of the complex are shown.

In the article present results of U-Pb — dating of zircons and petrologic-geochemical study of garnet-biotite plagiogneises and quartz-plagioclase-amphibole granofels host rocks samples from Vishnevogorsky sequence of the oldest rocks of the southern Urals Eastern domain are presented. U-Pb-dating of zircons were obtained by ion microprobe (SHRIMP II). The maximum age of the substrate plagiogneises Vishnevogorsky sequence not younger than 2700 Ma, and granulitic metamorphism plagiogneises falls on the Proterozoic age range 1740–2220 Ma. The dates obtained for plagiogneises and granofels Vishnevogorsky sequence reflect all major (PR1–P1) age stages of the Urals development. Many of the dated events are manifested only in the zircons generation and are not reflected in the mineral paragenesises of the studied rocks.

The results of U–Pb zircon dating, as well as the petrologic-geochemical study of samples of zircon-bearing garnet–biotite plagiogneiss and quartz—plagioclase–amphibole granofels from the Vishnevogorsky sequence of the oldest rocks of the Eastern domain of the Southern Ural are presented. The zircon ages were obtained using an ion microprobe (SHRIMP II). The maximum age of the substrate of plagiogneises in the Vishnevogorsky sequence is not younger than 2700 Ma and the granulite metamorphism of plagiogneiss falls in the Proterozoic age range of 1740–2220 Ma. The dates obtained for plagiogneisses and granofels of the Vishnevogorsky sequence reflect all major (PR 1 –P 1 ) age stages in the development of the Urals. Many of the dated events have manifested only in the zircon generations and are not reflected in the mineral parageneses of the studied rocks.

Èëüìåíñêèé ãîñóäàðñòâåííûé çàïîâåäíèê, Ìèàññ;

Research subject. This paper presents the results of a series of mineralogical, petrological, geochemical and isotope­chronological studies carried out to investigate metacarbonate­silicate rocks in the area of Ishkul Lake, the Ilmenogorsky complex.Materials and methods. The microprobe analysis of the composition of minerals was performed using a REMMA­202M scanning microscope equipped with a microanalyzer. The content of major, trace and rare­earth elements (REE) was determined using a mass spectrometer ICP­MS. The U­Pb age of zircons was obtained by a microprobe SHRIMP II. The content of REE in zircons was determined by an ion probe CAMECA IMS­4F.Results. The studied metacarbonate­silicate rocks are shown to be represented by spinel­forsterite­calcite, diopside­scapolite­calcite and clinopyroxenite varieties with a di verse range of minerals, including diopside, calcite, forsterite, spinel, scapolite, anorthite, enstatite, alumoenstatite, augite, fassaite, tschermakite, pargasite, hornblend, tremolite, barium­containing feldspar, celsian, phlogopite, graphite, titanite, fluorapatite, picroilmenite, pyrrhotite, pentlandite, sphalerite, violarite, gersdorffite, maucherite. In terms of petrochemical properties, the metacarbonate­silicate rocks under study are characterized by significant variations in the content of SiO2, CaO, MgO at a Ca/Mg ratio of 1.4–8.2, as well as by increased Ni and Cr content, low ratios of Sr/Ba, Th/U, Zr/Hf and Nb/Ta. The small ΣREE amounts of 6–25 ppm (rarely up to 70–72 ppm) correspond to sedimentary formations with a significant amount of ultrabasic material.Conclusions. The specific features of the composition of olivine, spinel, ilmenite, as well as the titanium content in the early generation zircon indicate the formation (transformation) of spinel­forsterite­calcite rocks at t = 830–850°C. According to the established specifics of REE distribution and the Th/U ratio, the early generation zircons refer to the granulite type zircons, while the late generation zircons correspond to those of transformed syenites­miaskites and various metasomatites. The formation (transformation) of the rocks is found to correspond to the following age stages: PR1 (1720–1780 Ma) ­ “granulite” metamorphism; D1–C (345–399 Ma) – metasomatic transformations caused by the formation of alkaline rocks associated with rifting processes; P1 (282 Ma) – tectonic­metasomatic transformations caused by shear processes.

Research subject. This paper presents the results of a series of mineralogical, petrological, geochemical and isotope­chronological studies carried out to investigate metacarbonate­silicate rocks in the area of Ishkul Lake, the Ilmenogorsky complex. Materials and methods. The microprobe analysis of the composition of minerals was performed using a REMMA­202M scanning microscope equipped with a microanalyzer. The content of major, trace and rare­earth elements (REE) was determined using a mass spectrometer ICP­MS. The U­Pb age of zircons was obtained by a microprobe SHRIMP II. The content of REE in zircons was determined by an ion probe CAMECA IMS­4F. Results. The studied metacarbonate­silicate rocks are shown to be represented by spinel­forsterite­calcite, diopside­scapolite­calcite and clinopyroxenite varieties with a di verse range of minerals, including diopside, calcite, forsterite, spinel, scapolite, anorthite, enstatite, alumoenstatite, augite, fassaite, tschermakite, pargasite, hornblend, tremolite, barium­containing feldspar, celsian, phlogopite, graphite, titanite, fluorapatite, picroilmenite, pyrrhotite, pentlandite, sphalerite, violarite, gersdorffite, maucherite. In terms of petrochemical properties, the metacarbonate­silicate rocks under study are characterized by significant variations in the content of SiO2, CaO, MgO at a Ca/Mg ratio of 1.4–8.2, as well as by increased Ni and Cr content, low ratios of Sr/Ba, Th/U, Zr/Hf and Nb/Ta. The small ΣREE amounts of 6–25 ppm (rarely up to 70–72 ppm) correspond to sedimentary formations with a significant amount of ultrabasic material. Conclusions. The specific features of the composition of olivine, spinel, ilmenite, as well as the titanium content in the early generation zircon indicate the formation (transformation) of spinel­forsterite­calcite rocks at t = 830–850°C. According to the established specifics of REE distribution and the Th/U ratio, the early generation zircons refer to the granulite type zircons, while the late generation zircons correspond to those of transformed syenites­miaskites and various metasomatites. The formation (transformation) of the rocks is found to correspond to the following age stages: PR1 (1720–1780 Ma) ­ “granulite” metamorphism; D1–C (345–399 Ma) – metasomatic transformations caused by the formation of alkaline rocks associated with rifting processes; P1 (282 Ma) – tectonic­metasomatic transformations caused by shear processes.

—Data on the mineralogy, geochemistry, and geochronology of zircons from plagioclase and spinel lherzolite and dunites of the Nurali massif are presented. The age of the main-type zircons from lherzolites (plagioclase ones, 446.2 ± 2.8 Ma, and spinel ones 433.3 ± 3.4 Ma) and dunites (443.8 ± 6.9 Ma) suggests their synchronous crystallization (Tav = 440 ± 5 Ma). The metamorphic age of zircons is 410–415 Ma. In addition to grains belonging to the main subset, the older grains with an age between 527 and 2045 Ma and newly formed metasomatic grains with an age of 380–385 Ma were found. The structure and REE patterns of most zircons from ultramafic rocks point to their magmatic origin, which is probably related to crystallization of a fluidized mantle melt.

ÂâåäåíèåÈëüìåíî-âèøíåâîãîðñêèé êîìïëåêñ (Þaeíûé Óðàë) ïðåäñòàâëÿåò ÷àñòü Èëüìåíî-Êàöáàõñêîé êîëëèçèîííîé ñòðóêòóðû («çîíû ñìÿòèÿ») øèðèíîé 20-25 êì è ïðîòÿaeåííîñòüþ íåñêîëüêî ñîòåí êèëîìåòðîâ

The formation time of 410.5 ± 1.1 Ma (zircon U/Pb SHRIMP) and the duration of rock crystallization (2–2.5 Ma) were determined for gabbro from the Nurali massif. The gabbro zircons showed a complicated polyphase structure. A new polygenous type of zonality including traces of primary growth and of the processes of crushing, dissolution, and substitution was discovered in the zircons. The formations of gabbro and ultramafites (lherzolites) of the massif are separated by a time break of 30–35 Ma determined by the genetic discontinuance.

ÂâåäåíèåÓëüòðàìàôèòîâûå ìàññèâû çàíèìàþò êëþ÷åâîå ïîëîaeåíèå â ãåîäèíàìè÷åñêîé èñòîðèè Óðàëà.Îäíèì èç îñíîâíûõ âîïðîñîâ èõ îáðàçîâàíèÿ/ïðåîáðàçîâàíèÿ ÿâëÿåòñÿ âîññòàíîâëåíèå òåðìîäèíàìè÷åñêèõ è âîçðàñòíûõ ïàðàìåòðîâ ôîðìèðîâàíèÿ èõ íèaeíåé ãèïåðáàçèòîâîé ÷àñòè.Ìàññèâû óëüòðàìàôèòîâ çîíû ñî÷ëåíåíèÿ Þaeíîãî è Ñðåäíåãî Óðàëà, ê êîòîðûì îòíîñÿòñÿ è óëüòðàìàôèòû èëüìåíî-âèøíåâîãîðñêîãî êîìïëåêñà, ðàññìàòðèâàþòñÿ êàê àëüïèíîòèïíûå, ïðåäñòàâëÿþùèå ñîáîé áëîêè âåðõíåé ìàíòèè [14].Óëüòðàìàôèòû èëüìåíî-âèøíåâîãîðñêîãî êîìïëåêñà (ÈÂÊ) ðàçâèòû â îñåâîé ÷àñòè êîìïëåêñà, â åãî âîñòî÷íîì è çàïàäíîì îáðàìëåíèÿõ

We present the data of geochemistry and geochronology of zircons from wehrlites and clinopyroxenites from dunite-wehrlite-clinopyroxenite bended complex of the base of crustal section of ophiolite Nurali massif. The U-Pb age of the bended complex is 450±4 Ma which is different from the previous data. Zircons from the studied rocks have complimentary REE patterns and similar U-Pb ages to lherzolites and dunites from mantle section of the Nurali massif.

The results of U–Pb zircon age dating of ultramafic massifs occurring as a chain along the Main Ural Fault zone (MUF) are given. Three groups of ages were obtained (Ma): 2500−2800, 600−2100, and 430−440. The first age group represents the time of origin of the ultramafic rocks in the Earth’s mantle. The second age group records the time of metamorphism of these rocks prior to intrusion into the host rocks. The third age group determines the time of the intrusion of ultramafic magma into the host rocks. It was established that the intrusion of ultramafic magma along the entire length of the Ural ultramafic belt occurred in the age range of 430−440 Ma.

Object. In the article presents the the results of mineralogy, geochemistry and isotope-chronological investigation of zircons from gabbro Nurali massif. Materials and methods . Amphibole gabbro is the fine-grained and massive texture rock, which cosists of hornblende, the base plagioclase and epidote. The contents of REE in the gabbro significantly exceeds their content in associated ultramafites of the massif. The content of REE and trace elements in zircons was determined by the method of secondary ion mass spectroscopy on the CAMECA-IMS-4F device. U-Pb date of zircons was obtained on the SHRIMP II microprobe. Results. Different variants of complex multiphase zonal structure of gabbro zircons are established. Along with the well known classical fine- and coarse-zonal kinds, a new type of zoning - “polygenic” - is distinguished. It combines the features of both primary growth and superimposed processes. The basis of the material evolution of zircons is progressive process of growth of their refining, reduction of U, Th and REE in later generations. These changes do not go beyond the boundaries of a single geochemical space, due to the connection with a single source. The mechanism of formation of successive zircon generations reflects the anatectic origin of gabbro. The age of zircons from gabbro is 410.5 ± ± 1.1 Ma for the duration of the process of crystallization of rock - 2.0-2.5 Ma. There is on 30-35 million years younger than the zircon from lherzolites of the massif. Conclusion .We consider that this indicates a lack of genetic links between them. The history of the development of gabbro is not associated with the formation of the ultramafic massif.

The data on the geochemistry and geochronology of zircons from wehrlites and clinopyroxenites of the dunite–wehrlite–clinopyroxenite banded complex that lies at the base of the crustal section of the ophiolite complex of the Nurali massif are presented. The obtained U–Pb age of the banded complex of 450 ± 4 Ma differs markedly from the previous age data. According to REE distribution patterns zircons from ultramafic rocks are attributed to the magmatic type and they indicate the age and supposed genetic similarity of the above rocks with lherzolites and dunites from the mantle section of the Nurali massif.

The problem of the U–Pb age of zircon crystals from ultrabasic rocks is discussed in this paper. It is shown that the assumption on the xenogenic nature of zircon crystals in dunite is not consistent with the petrographic and experimental data. The results of experimental study of the zircon–baddeleyite transition and thermodynamics of the reaction of zircon replacement with baddeleyite show that these transformations are the likely way of the formation of zoned zircon crystals in dunite. Each zone of these crystals may have its own age.