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Tait J.,University of Edinburgh | Zimmermann U.,University of Stavanger | Miyazaki T.,Japan Agency for Marin Earth Science and Technology | Presnyakov S.,All Russian Geological Research Institute VSEGEI | And 3 more authors.
Geological Magazine | Year: 2011

High-precision SHRIMP U-Pb zircon dating yields a late Palaeoarchaean age (3290 ± 8.6 Ma) for a large, unmetamorphosed, weakly peraluminous TTG body (the Keonjhargarh-Bhaunra pluton) in the Singhbhum craton of eastern India. One inherited subhedral zircon grain gave a concordant age of 3495.9 ± 5.3 Ma and Nd isotope characteristics show a juvenile trend with εNd t ∼ 0 and TDM 3395-3453 Ma. The data support a model of typical Archaean crustal evolution until late Palaeoarchaean times for the Singhbhum craton, which is in contrast to the more southerly Bastar craton where Palaeoarchaean non-TTG granites have been identified. These data demonstrate the diachronous development of continental crustal blocks now forming the basement of the eastern and central peninsular of India. © Cambridge University Press 2010.


Schenker F.L.,ETH Zurich | Schenker F.L.,University of Lausanne | Burg J.-P.,ETH Zurich | Kostopoulos D.,National and Kapodistrian University of Athens | And 3 more authors.
Tectonics | Year: 2014

The magmatic history of the Pelagonian Zone, in northern Greece, is constrained with secondary ion mass spectrometer (SIMS) U-Pb dating on zircons of various granitoids whose structural positions were defined with respect to the regional main foliation. Ages pertain to four groups: (i) Mesoproterozoic (circa 1430Ma) crystallization of granites inferred from inheritedmagmatic zircon cores that have been partially molten during the (ii) Neoproterozoic at circa 685 Ma (metamorphic zircon rims) and subsequently intruded by a Neoproterozoic leucogranite (circa 600Ma). (iii) Late- or post-Variscan calc-alkaline granitoids (315-301 Ma) were in turn intruded by a subvolcanic dike at about 280 Ma. In the Early Permian the εNd(t) in magmas decreased from -7.3 to -1.3, hinting to mantle-derived melts produced during extension. Rifting is further heralded by two acidic and one mafic dike containing Lower-Middle Triassic zircons (246-242 Ma). (iv) Early Cretaceous anatecticmelts at 117± 8 Ma formed during regional metamorphism. This age is the first report of in situ anatexis in the Pelagonian Zone. Cretaceous anatexis developed during the Mesozoic collision of Pelagonia with the Eurasian margin. Major- and trace-element geochemistry of amphibolites further attests for the complex pre-Alpine tectonic history with Neoproterozoic calc-alkaline and back-arc geochemical signature and Triassic alkali-magmatism. ©2014. American Geophysical Union. All Rights Reserved.


Bugrova I.Y.,Saint Petersburg State University | Bugrova E.M.,All Russian Geological Research Institute VSEGEI
Stratigraphy and Geological Correlation | Year: 2015

This work summarizes updated data on Paleocene and Lower Eocene deposits of the Crimean Peninsula concerning the systematics of assemblages of small foraminifers (and partly data on other microfossils) and results of biostratigraphic subdivision of sections. It is shown that Lower Paleocene and Lower–Middle Eocene deposits accumulated during two cycles of carbonate sedimentation in a warm-water shallow basin. These deposits are separated by Upper Paleocene deep-water deposits. The systematic composition of foraminifers testifies that there were different facies conditions in different parts of the Crimean basin and its connection to Western European and Tethyan basins during the Paleocene–early Eocene. © 2015, Pleiades Publishing, Ltd.


Sakoulina T.S.,JSC Sevmorgeo Rosnedra | Pavlenkova G.A.,Russian Academy of Sciences | Kashubin S.N.,All Russian Geological Research Institute VSEGEI
Russian Geology and Geophysics | Year: 2015

The 1370 km long 4-AR reference profile crosses the North Barents Basin, the northern end of the Novaya Zemlya Rise, and the North Kara Basin. Integrated geophysical studies including common deep point (CDP) survey and deep seismic sounding (DSS) were carried out along the profiles. The DSS was performed using autonomous bottom seismic stations (ABSS) spaced 10-20 km apart and a powerful air gun producing seismic signals with a step size of 250 m. As a result, detailed P- and S-wave velocity structures of the crust and upper mantle were studied. The basic method was ray-tracing modeling. The Earth's crust along the entire profile is typically continental with compressional wave velocities of 5.8-7.2 km/s in the consolidated part. Crustal thickness increases from 30 km near the islands of Franz Josef Land to 35 km beneath the North Barents Basin, 50 km beneath the Novaya Zemlya Rise, and 40 km beneath the North Kara Basin. The North Barents Basin 15 km deep is characterized by unusually low velocities in the consolidated crust: The upper crust layer with velocities of 5.8-6.4 km/s has a thickness of about 15 km beneath the basin (usually, this layer wedges beneath deep sedimentary basins). Another special property of the crust in the North Barents Basin is the destroyed structure of the Moho. © 2015.


Galli A.,ETH Zurich | Le Bayon B.,ETH Zurich | Le Bayon B.,Bureau de Recherches Géologiques et Minières | Schmidt M.W.,ETH Zurich | And 4 more authors.
Contributions to Mineralogy and Petrology | Year: 2012

Permian granulites associated with noritic intrusions and websterites are a common feature of the post-Variscan European crust. Such granulites are common in the Southern Alps (e. g. Ivrea Zone), but occur only in the Gruf Complex in the Central Alps. To understand the geotectonic significance of these granulites, in particular in the context of Alpine migmatisation, zircons from 15 high-grade samples have been U-Pb dated by SHRIMP II analysis. Oscillatory zoned zircons from charnockite sheets, interpreted as melts generated through granulite facies fluid-absent biotite melting at 920-940°C, yield ages of 282-260 Ma. Some of these zircons contain inclusions of opx, unequivocally attributable to the granulite facies, thus confirming a Permian age for the charnockites and associated granulites. Two samples from an enclave-rich orthogneiss sheet yield Cambrian and Ordovician zircon cores. Two deformed leucogranites and six ortho- and augengneisses, which compose two-thirds of the Gruf Complex, give zircon ages of 290-260 Ma. Most zircons have milky rims with ages of 34-29 Ma. These rims date the Alpine amphibolite facies migmatisation, an interpretation confirmed by directly dating a leucosome pocket from upper amphibolite facies metapelites. The Gruf charnockites associated with metre-scale schlieren and boudins of opx-sapphirine-garnet-granulites, websterites and gabbronorites can thus be identified as part of the post-Variscan European lower crust. A geotectonic reconstruction reveals that this piece of lower crust stranded in the (European) North upon rifting of the Neotethys, such contrasting the widespread granulite units in the Southern Alps. Emplacement of the Gruf lower crust into its present-day position occurred during migmatisation and formation of the Bergell Pluton in the aftermath of the breakoff of the European slab. © 2011 Springer-Verlag.


Vozarova A.,Comenius University | Smelko M.,Comenius University | Paderin I.,All Russian Geological Research Institute VSEGEI | Larionov A.,All Russian Geological Research Institute VSEGEI
Geologica Carpathica | Year: 2012

U-Pb dating (SHRIMP) of magmatic zircon ages from the Northern Gemericum Permian volcanics (Petrová Hora Formation) yielded the Concordia age of 272.4 ± 7.3 Ma for basaltic andesite, as well as the Concordia age of 275.2 ± 4 Ma for rhyodacites. Both zircon ages correspond to the Cisuralian Epoch in the time span of the Kungurian Stage. Acquired 206Pb/238U zircon age data support the nearly contemporaneous origin of the acid and basic volcanogenic members in the Northern Gemericum Permian strata. The bimodal volcanic suite proves the transtension/extension tectonic regime in the North Gemeric sedimentary basin during the Late Cisuralian. The magmatic zircon ages of rhyodacites, occurring in the lower thrust sheet of the Bôrka Nappe (Jasov Formation), gave a younger Concordia age of 266 ± 1.8 Ma proving the Guadalupian Epoch, in the time span of the Wordian/Capitanian. In comparison to the Northern Gemericum realm, this age refers to the relatively younger stage of rift-related extensional movements. In the wide Alpine-Dinarides realm the Middle Permian (Guadalupian) movements are related to the beginning of the Alpine sedimentary cycle. Thus, the Middle Permian rifting expresses the beginning of the formation of the future Meliata oceanic trough.


Duchesne J.-C.,University of Liège | Liegeois J.-P.,University of Liège | Liegeois J.-P.,Royal Museum for Central Africa | Bolle O.,University of Liège | And 4 more authors.
Lithos | Year: 2013

Granite and dolerite occurring in the eastern unit of the Maures Massif (southern France Variscan belt) were emplaced in the waning stage of the evolution of a dextral shear zone along the Gondwana border with Laurasia. We present a geochronological and petro-geochemical study (major and trace elements, Sr-Nd isotopes) of (1) the foliated Moulin Blanc cordierite granite and related foliated dykes; (2) the equant Camarat granite and dyke; and (3) the andesite-basalt dolerite dykes (frequently mingled with leucogranite material at Pinet and Capon tips) and cross-cutting leucogranitic dykes. Zircon and monazite dating of the Moulin Blanc granite gives a crystallization age of 301±2Ma. SHRIMP dating on zircons from the leucogranite component of a Pinet composite dyke only reveals zircon core ages of mainly 310±10Ma (age of migmatization of the host gneiss). Undulating contacts of dolerite dykes within the c. 300Ma old Camarat granite suggest penecontemporary relationships between the two intrusions. The age interval between the Moulin Blanc granite and the dolerite dykes would thus be very short. The Moulin Blanc pluton is formed by mingling and mixing of melts of granitic and dioritic composition, the latter occurring mainly as microgranular mafic enclaves. Two other types of diorites are also identified in the pluton. The foliated dykes are similar in composition to the Moulin Blanc granite, which confirms their relationship to the main pluton. The Moulin Blanc granite is a typical example of a pluton formed by repeated recharges coming from a deeper magma chamber. Formation of the Camarat dykes is controlled by hydrothermal fluids that are responsible for the non-CHARAC behavior of trace elements. The Pinet and Capon leucogranite components of the dolerite dykes have distinct geochemical signatures, different from the Camarat granite and dykes. The cross-cutting leucogranitic dykes have much geochemical similarities with the Capon granite. The age of similar dykes in the Tanneron Massif supports the contemporaneity of Camarat granite and dolerites. The dolerite geochemistry was deeply modified by alteration processes, but an andesite-basalt composition is still recognizable by using immobile element ratios. In a εNd vs. Sri diagram, all rocks plot close to a mixing hyperbola between a depleted mantle component and a crustal component, characteristic of the Variscan crust in the French Massif Central. There is a broad correlation between the NdTDM 2-stage model ages and the degree of fractionation of the rocks. Modeling of dehydration melting in a range of P-T conditions reveals that a variety of lithologies were the source of the Saint-Tropez magmas: high-alumina and alkali-basalt amphibolites, metagraywackes, metapelites and meta-arkoses. These sources were melted almost simultaneously at different levels in the crust. The calculated critical dyke width required to transport the granitic melt by buoyancy is far too large compared to the observed granitic dyke thicknesses. Therefore, tectonic processes and/or melt overpressure must have played a role in the emplacement mechanism. Thermo-mechanical constraints on mixing between mafic and felsic melts suggest that, in the Pinet composite dykes, both melts should have mixed. The observed lack of mixing is interpreted as due to quick cooling. The region was affected by a hot zone at the end of a transpressional regime. © 2013 Elsevier B.V.


Shatov V.V.,All Russian Geological Research Institute VSEGEI | Moon C.J.,Rose Cottage | Moon C.J.,University of Exeter | Seltmann R.,Natural History Museum in London
Journal of Geochemical Exploration | Year: 2014

Rock geochemical surveys have been widely used for mineral exploration in Russia and more generally, the former Soviet Union. Some conducted by VSEGEI have in addition to geochemistry, determined quantitative petrography on the survey samples.In the case described, a regional survey in the Yubileinoe area southern Urals of Kazakhstan has been undertaken to investigate a district which has both the characteristics of volcanic associated massive sulphide and porphyry style mineralisation. Samples were collected on a 500. m or tighter grid over a 10. ×. 10. km area and analysed by direct current arc spectrometry as well as quantitative mineral determination on thin sections. The combination of these techniques was used to determine elemental loss and gain relative to host rocks in addition to alteration facies. GIS techniques were also used to investigate the spatial variation of geochemical and mineral primary concentrations.Although the porphyry deposit at Yubileinoe gives a clear signature, software based discrimination of alteration into VMS and porphyry types allows better targeting for follow-up. The porphyry signature is detectable for approximately 350. m into wallrock in mono-element data, notably Cu and Au. Multiplicative haloes are of similar magnitude although less noisy. This approach also allows the mapping of alteration facies and combination into loss and gain maps as well as a prognostic map of mineral deposit potential.The use of manual quantitative mineralogy is prohibitively expensive where labour is costly. However the advent of computer-based methods means that this approach may well be viable in the future. © 2014 Elsevier B.V.


Based on an analysis of the significant collections of Favositidae (tabulate corals) from the Upper Ordovician-Lower Devonian of the Taimyr Peninsula, Western Slope of the North Urals and the Tchernychev Uplift, this paper focuses on the macro- and micro-structurye{cyrillic} of the corallite wall. Seven structural types of the corallite wall have been recognized; some of them seem to have a definite stratigraphic range. The results contribute to the long-time discussion on the applicability of skeletal structure for systematics of the Favositidae, its evolutionary implications, and stratigraphic correlation. It has been held that the skeletal structure of the fossilized remains of Favositidae is inapplicable for such purposes because diagenetically, it is secondary, being a product of mineral replacement of the primary structure. In contrast, an assumption is made here that the " secondary" skeletal macro- and micro-structure may reflect in some way the " primary" skeleton. As a result, it is proposed that some evidence of evolution of the Favositidae may be obtained by evaluating the stratigraphic range of favositid representatives possessing different types of structure of the corallite wall. © 2010 Elsevier Ltd and Nanjing Institute of Geology and Palaeontology, CAS.


Bugrova E.M.,All Russian Geological Research Institute VSEGEI | Starshinin D.A.,All Russian Geological Research Institute VSEGEI
Stratigraphy and Geological Correlation | Year: 2013

In Northeastern Tajikistan (Peter I Ridge), we have studied the foraminifer complex in the sulfatecarbonate deposits of the Shikerga Member, previously regarded as Jurassic. According to the data obtained, the age of the Shikerga Member is considered to be Paleocene. An analysis of the faunal remnants and rock composition makes it possible to suggest that an intracontinental basin existed in the studied area in the Paleocene. Sometimes, waters of the Tethys Ocean, settled by planktonic and thermophilic benthic foraminifera, penetrated into the Tajik Depression. © 2013 Pleiades Publishing, Ltd.

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