U-Pb zircon age of a sheeted dike complex in ophiolites in the structure of the Revdinsky massif, Ural Рlatinum Belt

Research subject. A tectonic block of ophiolites, corresponding to the root zone of a sheeted dike complex, in the eastern part of the Revdinsky massif of the Platinum-bearing belt of the Urals (UPB).Materials and methods. Zircons for dating were collected in the first-generation dolerite dikes of the sheeted dike complex under study, which had been previously considered as Ordovician. U-Pb dating of zircons was performed by LA-ICP-MS on a NexION 300S quadrupole mass spectrometer with a laser ablation attachment NWR 213.Results. Zircons with an age of 425.6 ± 2.9 Ma are characterized by primary magmatic zoning and apparently correspond to the time of intrusion of the sheeted dike complex. In zircons with an age of 404.0 ± 2.9 Ma, inclusions of metamorphogenic minerals (amphibole, chamosite, quartz, clinozoisite) were discovered. This age reflects rock recrystallization or metamorphism, for example, during the intrusion of later vein rocks of the diorite-tonalite series or dolerite dikes of the second generation. Three points of determination showed a younger age of 362 ± 5.6 Ma, probably reflecting the time of metamorphism at the beginning of collisional processes. Conclusions. For the first time, the Silurian U-Pb age of zircons (LA-ICP-MS) was obtained for the ophiolite block (root zone of the sheeted dike complex) in the structure of the Revdinsky massif UPB. The obtained age of intrusion of the sheeted dike complex (425.6 ± 2.9 Ma) coincides with the age of zircons (428.5 ± 3.7 Ma) from gabbro screens in sheeted dikes of the East Ural zone determined earlier (Smirnov, Ivanov, 2010) and corresponds to the time of spreading over the subduction zone in the Middle Urals.

Рудно-метасоматическая зональность молибден-порфировой системы Аксу (Северо-Восток Азии)

The article presents the data from a comprehensive study of the Aksu Mo-porphyry system metasomatites (Korkodon-Nayakhan magmatic activation zone). The halo of metasomatic changes around the porphyry system, associated with the tectonic-block structure of the territory, is shown to be asymmetric. The core of the system is brought to the surface and located in a halo of kalifeldspar- muscovite metasomatites; the northwestern block is elevated and characterized by high-temperature epidote-biotite and epidote-pyroxene propylites, while in the southeastern block there is a consistent transition from kalifeldspar-sericite metasomatites to fragments of argillisite ones. The established zoning is confirmed by geochemical associations and mineralization types from the northwest to the southeast: in the northwest, Au-Bi (As, Cu) at the Solnechnoye ore occurrence; in the center, Mo (Cu, Au) at the Aksu deposit; in the southeast, Ag-Pb-Zn (Cu, Bi, As, Au) at the Vysokoye ore occurrence.

Upper Devonian brachiopods from the core of the Kurgan-Uspenskaya-1 key borehole (south-western outlying areas of Western Siberia)

Research subject. Brachiopods from the core of the Kurgan-Uspenskaya-1 parametric borehole. The borehole was drilled in the south of Western Siberia 80 km southeast of the Kurgan town. Brachiopods were collected at a depth of 1,525.4 m in the IV tectonic block (core interval 1,450–1,794 m) in the greenish-gray marls of the Famennian stage of the Upper Devonian.Materials and methods. The paleontological material is presented in the form of complete undamaged shells and individual valves of small- and medium-sized brachiopods. The safety of brachiopods makes it possible to determine their species and genera, sometimes in open nomenclature. The article provides a brief description of the available material.Results. 11 species of brachiopods of the subtype Rhynchonelliformea belonging to six orders and nine genera were identified. The following ten species were described: Orbinaria fallax (Pand.), Semiproductus amplus Bubl., Schuchertella sp., Dalejina? sp., Camarotoechia panderi (Sem.et Moell.), C. volucera Nal., Athyris tobolica Nal., Cleiothyridina tenuilineata (Row.), Cl. ex gr. pectinata (Sem. et Moell.), Retzia? sp. The presented information allows conclusions about the age of the sediments enclosing the brachiopods under study and expands the existing knowledge of both the composition of the Upper Famennian brachiopods of the basement of the south of Western Siberia and their geographical and stratigraphic distribution.Conclusion. An analysis of the stratigraphic distribution of the described brachiopods taking into account data on foraminifera allowed us to determine the age of the host rocks as the very top of the Famennian stage. The composition of the brachiopods allows these rocks to be correlated with coeval deposits of the East European Platform, Timan, the Urals, Kuzbass, the Gorny Altai, Kazakhstan and North America.

Geomorphological and Statistical Assessment of Tilt-Block Tectonics in the Garhwal Synform: Implications for the Active Tectonics, Garhwal Lesser Himalaya, India

Active tectonics is manifested in geomorphological features such as drainage basins and drainage patterns. Geomorphic parameters asymmetry factor (AF) and transverse topography symmetry factor (T) is calculated for 94 third order basins of the Garhwal synform to decipher the tilt-block tectonics based on remote sensing and geographical information system (GIS) techniques. The quantitative analysis of the AF suggests that all the 94 basins are asymmetric and gentle to steeply tilted, indicating active tectonics and early and late stage of development, respectively. The mean vector magnitude (θv) of T suggests the migration of the basin stream towards the south in most basins (60%), suggesting a unidirectional tilting of the tectonic block. The χ2 test for statistical significance indicates that the θv is significant for southern and northern limb basins. The χ2 test affirms that the third order basin position on either side of the main channel of the river basin influences the tilt direction. The regional tectonics suggests migration of the Lansdowne klippe towards the south, as the majority of third order basins show southward tilt. The study provides a quick appraisal of tilting in the tectonic blocks of active margins, such as in the Himalayas.

SEISMIC MODEL OF THE UPPER EARTH`s CRUST ON NORTH-EAST PART OF TRAVERSE 3-DV BASED ON RESULTS OF HEAD WAVES DIGITAL PROCESSING

Digital processing of refracted waves data, which are registered on North-East part of profile3-DV, is done. Time sections and velocity model are formed. It is proved, that refraction horizons on depth interval of 0-1.5 km are geologic boundaries in sedimentary cover on Ayan-Yuryakh tectonic block. Refraction boundary on depth of ~1.0 km is not lithologic border on Inyaly-Debin block. Layers, which are potentially productive for ore mineral resources, are substracted by low values of V/V (1.66-1.70) on depth below 1.0 km, on Inyaly-Debin block and Orotukan-Balygychan elevation.

KORDONKA TERRANE — A FRAGMENT OF THE EARLY PALEOZOIC ACTIVE MARGIN

The Kordonka Formation (lower Silurian) forms a lens-shaped tectonic block up to four km wide, extending southward from the Pogranichny village area (Primorsky Krai) for about 30 km. The formation is composed of argillaceous slate, volcanic-sedimentary rocks with horizons of sandstones, siltstones, conglomerates, and cherts, and also contains flows of basalts and andesite-basalts. The results of lithological-geochemical study of the terrigenous rocks of the formation indicate that the Kordonka Formation was accreted in the outer pre-oceanic part of the paleo-island arc system. The eastern part of the formation is intruded and partially assimilated granitoids of Middle Paleozoic and Late Permian age. The early phase of the granitoids was dated by U-Pb zircone 373.5±1.7 and 383.5±1.6 Ma (Late Devonian). The late phase is characterized by 261.2±1.2, 257.4±0.93 and 261.5±1.6 Ma (Wuchiapingian and Capitanian stages of the Middle and Late Permian). The Devonian granitods first identified in this area may be evidence of the Kordonka block accession to the Bureya-Jiamusi-Khanka orogenic belt consolidated during the Ordovician. The Kordonka terrane thus marks an independent Early-Middle Paleozoic episode in the formation and closure of the Central Asian paleo-ocean.