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Konopelko D.,Saint Petersburg State University | Biske G.,Saint Petersburg State University | Seltmann R.,Natural History Museum in London | Petrov S.V.,Saint Petersburg State University | Lepekhina E.,Russian Geological Research Institute VSEGEI
Ore Geology Reviews | Year: 2014

Neoproterozoic volcanics and granitoids formed at Rodinia margins within a time span of 880Ma-700Ma, are well-documented in many terranes of the southern Central Asian Orogenic Belt (CAOB). Ages younger than 550Ma corresponding to the opening of the Terskey Ocean are also common. However, so far, there were very few published ages in the range 700Ma-550Ma from the Kyrgyz Tien Shan. In this paper we present new data for the alkaline Chon-Ashu complex emplaced at the end of the Cryogenian Period of the Neoproterozoic (850-635Ma, Gradstein et al., 2012). The alkaline complex intrudes the Precambrian metamorphic rocks north of the Nikolaev Line which separates the Northern and Middle Tien Shan terranes in the eastern Kyrgyzstan. The undeformed shallow level alkaline rocks range from olivine gabbro to nepheline and cancrinite syenites and leucosyenites. The differentiated rock assemblage can be explained by fractional crystallization of high-silica mineral phases which drives nepheline-normative melts away from the silica saturation boundary. The alkaline rocks of Chon-Ashu are enriched in LILE and HFSE indicative of their origin from lithospheric mantle. An age of 678±9Ma (U-Pb, SHRIMP) was obtained for a protolith of country gneiss, and an age of 656±4Ma was obtained for the crosscutting alkaline rocks of the Chon-Ashu complex. Seven zircon grains recovered from gneiss and alkaline rocks had bright overgrown rims which yielded a cumulative age of 400±8Ma. A metamorphic event, followed by uplift and emplacement of shallow level alkaline complex, constrains the geodynamic setting. Alkaline rocks usually form in an extensional setting and originate from lithospheric mantle. The 690Ma xenoliths of mafic granulite from the NW Tarim have been interpreted to originate by mafic underplating. This mafic underplating may have been responsible for metamorphism in the middle crust prior to emplacement of the Chon-Ashu complex. The 670Ma-630Ma period of extension and emplacement of enriched alkaline rocks can be also traced on a regional scale through southern Kazakhstan and the northern Tarim. We tentatively interpret these events as a result of mafic underplating and subsequent rifting related to the break-up of Rodinia. During field work at Chon-Ashu, rich chalcopyrite mineralization has been discovered in carbonate veinlets in leucosyenite alkaline dikes and has also been found in the adjacent Cambrian gabbro and granites shown on the map as undivided Devonian-Silurian. Stockwork mineralization predominates though disseminated mineralization is also present. The Cu content reaches 16,184ppm and is associated with elevated concentrations of Pb, Zn and Ag. The polyphase structural evolution of the area suggests that mineralization could have formed in several genetically unrelated stages. Based on structural and mineralogical evidence we tentatively relate the earliest stage of chalcopyrite mineralization to the late magmatic CO2-rich fluids emanating from the Cryogenian alkaline complex. The Early Devonian thermal event registered by growth of new zircon at 400Ma has important metallogenic implications on a regional scale. However the origin of two zones of alteration in the undivided Silurian-Devonian granites is ambiguous because their age was not determined geochronologically. The 522±4Ma Cambrian gabbro of the Tashtambektor Formation is strongly foliated along the splays of the Nikolaev Line, indicating a Hercynian origin of the fabric. Superimposed mineralized stockwork postdates the foliation and suggests a late-Hercynian age of mineralization in gabbro. The new data enable a reassessment of the metallogenic potential of the Eastern Kyrgyz Tien Shan. Presence of not eroded high-level mineralized Neoproterozoic alkaline intrusions points to a previously underestimated metallogenic potential of pre-Hercynian granitoids which may host preserved porphyry systems, skarns and shear-related mineralization. Finally, the Devonian magmato-metamorphic event which caused formation of a number of ore deposits in central Kyrgyzstan and Kazakhstan could also create potential exploration targets in eastern Kyrgyzstan. © 2014 Elsevier B.V.

Hairapetian V.,Islamic Azad University at Khorasgan | Pour M.G.,Golestan University | Popov L.E.,National Museum of Wales | Modzalevskaya T.L.,Russian Geological Research Institute VSEGEI
Estonian Journal of Earth Sciences | Year: 2012

A Llandovery (mid-upper Aeronian) brachiopod fauna is described for the first time from the Niur Formation of Central Iran. It is dominated by two succeeding rhynchonellide species Stegocornu procerum Ḑrkoop, 1970 and Stegocornu denisae sp. nov. In addition, there are three common and four rarer brachiopod species, including Dalejina? rashidii sp. nov., Isorthis (Ovalella) inflata sp. nov. and Striispirifer? ocissimus sp. nov. The Stegocornu Association gives a distinct biogeographic signature to the mid to late Llandovery rhynchonellide-dominated shallow-water brachiopod faunas of Central Iran, Kope-Dagh and Afghanistan. Its proliferation in temperate latitude peri-Gondwana was one of the earliest signs of biogeographical differentiation of the brachiopod faunas in the early Silurian. The affinities of Stegocornu and Xerxespirifer are discussed.

Vdovets M.S.,Russian Geological Research Institute VSEGEI | Silantiev V.V.,Kazan Federal University | Mozzherin V.V.,Kazan Federal University
Geoheritage | Year: 2010

The area, which occupies the right bank of the Volga River from the mouth of its tributary, Sviyaga River, to the southern border of Tatarstan, and the right bank of the Kama River from its mouth to the northeastern border of Tatarstan, is considered to warrant the possible creation of a national geopark. The area is characterized by well-defined limits, and it occupies 2,080 km2 that is commensurate with an area of many successfully functioning geoparks. It has more than 150 years of history of comprehensive geological studies carried out by prominent Russian and foreign geologists. A significant number of geosites (29) of different types and significance levels accessible to visitors are revealed there. The majority of the geosites are of interest first of all in terms of stratigraphy and palaeontology as well as geomorphology, tectonics, petrology, hydrogeology, and history of geology and mining. These geosites allow study of the history of the Earth's organic world in the Middle-Upper Permian, geological events, and processes that occurred in this region, as well as landform evolution. This area is of aesthetic value owing to the variety and beauty of its natural landscapes. It also contains abundant nongeological natural, historical, and cultural heritage sites attractive for tourists. It is also characterized by a high level of economic development, well-developed infrastructure, and the existence of officially protected sites that occupy a fifth of the territory. The area is of high educational significance as well. It has, for a long time, been used as a geological training ground for students of the Kazan State University, Russia. Moreover, the scientific and methodical basis for seven educational-excursion routes including visiting particularly interesting geological, historical, and cultural sites of the planned geopark has been already developed. The comprehensive evaluation of this area shows that it meets all necessary criteria for geopark creation. © 2010 Springer-Verlag.

Ghavidel-syooki M.,University of Tehran | Alvaro J.J.,CSIC - National Institute of Aerospace Technology | Popov L.,Natural Museum of Wales | Pour M.G.,Golestan University | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

High-latitude Hirnantian diamictites (Dargaz Formation) and lower-Silurian kerogenous black shales (Sarchahan Formation) are locally exposed in the Zagros Mountains. The glaciogenic Dargaz deposits consist of three progradational/retrogradational cycles, each potentially controlled by the regional advance and retreat of the Hirnantian ice sheet. Glacial incisions of sandstone packages change laterally from simple planar to high-relief (<. 40. m deep) scalloped truncating surfaces that join laterally forming complex polyphase unconformities that scour into the underlying Seyahou Formation. The glaciated source area was to the present-day west, in the region of the Arabian Shield, where numerous tunnel valleys have been reported. Based on a study of palynomorphs and graptolites, the glaciomarine Dargaz diamictites are dated as Hirnantian, whereas the youngest Sarchahan black shales are diachronous throughout the Zagros, ranging from the Hirnantian persculptus to the earliest Aeronian (Llandovery) triangulatus zones. The diachronism is related to onlapping geometries capping an inherited glaciogenic palaeorelief that preserved different depth incisions and source areas. Our data suggest the presence of Hirnantian satellite ice caps adjacent the Zagros margin of Arabia and allow us to fill a gap in the present knowledge of the peripheral extension of the Late Ordovician ice sheet. © 2011 Elsevier B.V.

Konopelko D.,Saint Petersburg State University | Kullerud K.,University of Tromso | Apayarov F.,North Kyrgyz Geological Expedition | Sakiev K.,National Academy of science | And 3 more authors.
Gondwana Research | Year: 2012

In this paper we present the first results of sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating obtained for the ultra-high pressure (UHP) metamorphic rocks of the Makbal metamorphic complex in the Northern Tien Shan, Kyrgyzstan. Zircon grains from two HP eclogite samples and one sample of UHP garnet-talk-chloritoid schist have similar bright rims identified on cathodoluminescence (CL) images. The rims are interpreted as zircon overgrowth during UHP metamorphism. Dating of zircon rims from the three samples yielded similar ages of 509. ±. 7. Ma, 502. ±. 10. Ma and 498. ±. 7. Ma. The time span of 510-500. Ma is considered as the "minimum" age of UHP metamorphism of the Makbal complex. This age is in accordance with Middle Cambrian faunal age of the Kara-Archa ophiolite in the Makbal area. It is suggested that the Makbal rocks were metamorphosed in the Middle Cambrian subduction zone dipping north under the Northern Tien Shan microcontinent. A deformed granodiorite associated with the Makbal metamorphic rocks yielded an age of 514. ±. 5. Ma, indicating development of a magmatic arc simultaneously with the UHP metamorphism. Cores of zircon grains from the garnet-talk-chloritoid schist yielded a wide spectrum of ages (1850-800. Ma) characteristic for detrital zircons of continental origin. A depositional age <. 800. Ma points to a possible derivation from a Riphean passive margin of the Terskey Ocean. Analyses of zircon grains from two eclogite samples fit well-defined discordia lines with upper intercepts at 1446. ±. 25. Ma and 1447. ±. 29. Ma, indicating a homogeneous Mezoproterozoic protolith of these rocks. The possible presence of such protoliths in Makbal is illustrated by a similar age of inherited zircon recovered from the granodiorite (1443. ±. 25. Ma) and by Mesoproterozoic detrital zircons from the garnet-talk-chloritoid schist. Ages of Kokchetav, Makbal, Aktyuz and Anrakhai HP-UHP complexes in the Kokchetav-Northern Tien Shan belt vary from 537 to 475. Ma and register subduction-accretion events during the Caledonian orogeny which finally formed the Paleo-Kazakhstan continent prior to Middle Ordovician. © 2011 International Association for Gondwana Research.

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