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1.
I. F. Gablina L. L. Demina O. B. Dmitrenko N. S. Os’kina E. A. Popova T. A. Khusid V. V. Shilov 《Oceanology》2011,51(3):476-490
The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic
Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms,
as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns
and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred
in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts.
The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal
activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone
of Fe-Mn crusts. 相似文献
2.
The South Armorican Shear Zone (SASZ), in the French Armorican Variscan belt, is a lithospheric wrench fault that acted during the Late Carboniferous as a transition zone between two distinct domains: a thickened domain to the south affected by extension and crustal magmatism, and a weakly thickened domain to the north subjected to dextral wrenching and crust- and mantle-derived magmatism. The Pontivy-Rostrenen complex is a composite intrusion emplaced along the SASZ. To the south, the complex is made of leucogranites whereas, to the north, monzogranites outcrop together with small intrusions of quartz monzodiorite. U-Pb dating of magmatic zircon by LA-ICP-MS reveal that most magmatic rocks were emplaced at ca. 315 Ma (between 316.7 ± 2.5 Ma and 310.3 ± 4.7 Ma), excepted a late leucogranitic intrusion that was emplaced at 304.7 ± 2.7 Ma. The leucogranites (− 4.8 < εNd (T) < 2.1; presence of Archean to Paleozoic inherited zircon) are strongly peraluminous (A/CNK > 1.1) and formed by partial melting of metasediments and peraluminous orthogneisses. The monzogranite (− 4.0 < εNd (T) < − 3.2; scarce Paleozoic inherited zircon) is moderately peraluminous (1 < A/CNK < 1.3) and formed by partial melting of an orthogneiss with a probable metaluminous composition whereas the quartz monzodiorite (− 3.2 < εNd (T) < − 2.2; no inherited zircon) is metaluminous (0.7 < A/CNK < 1.1) and formed by partial melting of a metasomatized lithospheric mantle. The evolution of the magmas was controlled by fractional crystallization, magma mixing and/or peritectic mineral entrainment. At the scale of the Armorican Variscan belt, crustal partial melting, to the south of the SASZ, was triggered by lithospheric thinning and adiabatic decompression during extension. Conversely, to the north, asthenosphere upwelling during strike-slip deformation and subsequent slab tearing, as suggested by tomographic data, induced the melting of both the crust and the mantle fertilized during previous subduction events. This process is likely not exclusive to the Armorican Massif and may be applied to other regions in the Variscan belt, such as Iberia. 相似文献
3.
This study provides 87Sr/86Sr, δ13C and δ18O data from the best-preserved limestone and dolomite of the Ediacaran carbonate-dominated Khorbusuonka Group of the Olenek Uplift, NE Siberian Craton, as well as detrital zircon geochronological data from both underlying and overlying sandstones. The Maastakh Formation is characterized by 87Sr/86Sr ratios of ca. 0.70822 and δ13C values between + 4.8 and + 6.0‰. 87Sr/86Sr ratios in limestones of the Khatyspyt Formation are fairly uniform, ranging from 0.70783 to 0.70806. The carbon isotopic composition slowly decreases from bottom (+ 3.7‰) to top (− 0.2‰) of section. The Sr isotopic composition of the Turkut Formation varies from 0.70824 to 0.70914, value of δ13C is about zero: − 0.7…+0.7 ‰. The youngest population of detrital zircons from Maastakh Formation indicates that these rocks were formed not later than 630 Ma. U–Pb detrital zircons data of Kessyusa Group has a single peak at about 543 Ma, which is almost identical to the earlier dating. Based on biostratigraphy and isotopic data, the Sr isotopic compositions from the Khatyspyt Formation (87Sr/86Sr = 0.70783–0.70806) represent the composition of seawater at 560–550 Ma. Such low values of 87Sr/86Sr ratio in Ediacaran water were probably caused by the quick opening of Iapetus Ocean. 相似文献
4.
Synchronous observations of the electrotelluric field were performed on the lake ice and the coast. The ice-based vertical/horizontal field ratio at periods of a few seconds to a few minutes ranges from a few hundredths to a few thousandths, which is comparable to the noise level. The results of these observations favor a plane wave model. At the coastal station, the vertical and horizontal fields are similar, which is related to geoelectric heterogeneity of the medium. An electric tipper is used to control the behavior of heterogeneity in the spectral-time domain. Anomalous changes associated with earthquakes of K ≥ 12 are revealed from data of the tipper monitoring at epicentral distances of up to 300 km. A longitudinal MTS curve free from the effect of local geoelectric heterogeneities is obtained from ice-based data. Deep conducting layers are recognized as minimums in this curve. 相似文献
5.
E. O. Groznova M. G. Dobrovol’skaya V. A. Kovalenker K. V. Davydov V. T. Bitarov M. V. Razin 《Geology of Ore Deposits》2006,48(2):108-133
The mineralogy and PT formation conditions of the Dzhimidon Pb-Zn deposit in the Sadon ore district are considered. The deposit is localized in metamorphic rocks of the Buron Formation, which pertain to the pre-Jurassic basement (lower structural stage) and are cut through by Upper Paleozoic granitoids, and in the Lower Jurassic terrigenous sequence (upper structural stage). Orebodies as quartz-sulfide veins are mainly hosted in the metamorphic rocks. Galena, sphalerite, chalcopyrite, pyrite, pyrrhotite, and arsenopyrite are the most abundant sulfides, while quartz, carbonates, chlorite, sericite, and feldspar are gangue minerals. The bismuth mineralization identified at this deposit for the first time is represented by diverse phases of the Ag-Pb-Bi-S system. Five stages of the ore deposit formation are recognized: a premineral stage (quartz-feldspar), three ore-bearing stages (pyrite-arsenopyrite, pyrrhotite-chalcopyrite-sphalerite, and arsenopyrite-sphalerite-galena), and a postmineral stage (quartz-calcite); each stage comprises one or several mineral assemblages. The study of fluid inclusions in quartz, calcite, and sphalerite of the premineral, ore-forming, and postmineral stages has shown that the ore was deposited mainly from Na chloride solution with a salinity varying from >22 to <1.0 wt % NaCl equiv at a temperature from 460 to ～120°C and 430–290 bars pressure. The third stage was characterized by an abrupt increase in temperature and by the appearance of Mg(Fe,Ca) chloride solutions equally with Na chloride fluids, presumably owing to the emplacement of granite porphyry. 相似文献
6.
V. N. Benyamovskiy A. S. Alekseev M. N. Ovechkina V. S. Vishnevskaya A. V. Podgaetskii V. G. Pronin 《Stratigraphy and Geological Correlation》2012,20(4):346-379
Four upper Campanian-lower Maastrichtian reference sections are described in the Glubokaya and Kalitva river basins and in the Znamenka 1-A Borehole located in the northwestern Rostov region. The sections are composed of the upper Campanian Kagal??nik, Belgorod, Pavlovka, Sukhodol and lower Maastrichtian Efremovo-Stepanovka formations. They are characterized by successive stratigraphically significant macro- and microfossil assemblages: belemnites, calcareous nannoplankton, benthic foraminifers, and radiolarians. The Pavlovka and, particularly, Sukhodol formations contain a specific assemblage of coarsely-agglutinated benthic foraminifers. The first data obtained on radiolarians in upper Campanian-lower Maastrichtian sections of the northwestern Rostov region revealed four assemblages, two of which were previously unknown from Upper Cretaceous sediments of the East European Platform. Most sections enclose a hiatus at the base of the Sukhodol Formation, which comprises two upper Campanian benthic foraminiferal zones. The problem of recognition of the lower Maastrichtian boundary on the East European Platform is considered in accordance with international GSSP requirements. 相似文献
7.
The Olkhon terrane is a part of the Early Palaeozoic accretionary-collisional system in the northern Central Asian Orogenic Belt (CAOB). The terrane was produced by an Ordovician collision as a collage of numerous chaotically mixed tectonic units composed of rock complexes of different ages originated in different tectonic settings. The pre-collisional history of the terrane is deciphered using new data on zircon ages and chemistry of rocks from several complexes. The oldest Olkhon rocks are the 1.87–1.83 Ga granulite and gneissic granites of the Kaltygey complex, which is an exotic Palaeoproterozoic tectonic slice. The next age group consists of the Ust-Zunduk orthogneisses (807 ± 9 Ma) and the Orso amphibolites and gneisses (792 ± 10 and 844 ± 6 Ma). Samples of both complexes have negative εNd(t) values. The Ust-Zunduk and Orso complexes can have formed in active margins of continents or in crustal blocks other than southern Siberia. The Ediacaran subduction-related rocks of the Olkhon complex may have formed in an island arc setting within the Palаeo-Asian Ocean (PAO). The protolith of schists after volcanic rocks has an age of 637 ± 4 Ma and shows positive ɛNd(t) values. The Ediacaran/Cambrian Tonta mafic granulites (ca.545 Ma), with OIB affinity and slightly positive ɛNd(t), were derived from an enriched mantle source and may represent a fragment of an oceanic island. The Cambrian Shebarta gneisses after continental-arc greywackes with negative ɛNd(t) values were deposited in a back-arc basin of a microcontinent within the PAO, between 530 and 500 Ма. The Cambrian Birkhin metamorphics after PAO mature island-arc rocks have U-Pb ages of ca. 500–490 Ma and positive ɛNd(t) values. All pre-collisional complexes in the Olkhon terrane have their analogues among the rocks formed during main events in the northern CAOB history. Thus the reconstructed milestones in the Olkhon terrane history appear to be an echo of events in the CAOB northern segment. 相似文献
8.
Stratigraphic position of the Oligocene-Miocene (Paleogene-Neogene) boundary in the northern Caucasus and, in this connection, of the Alkun Formation and the Caucasian regional stage in geological sections of Maikop deposits, primarily in those of the Belaya and Kuban rivers, is considered. Arguments in support of the Caucasian regional stage are presented and necessity of distinguishing the Karadzhalganian regional stage is called in question. Stratigraphic implications of the Alkun Formation, the regional reference horizon traceable in many sections of the northern Caucasus, are discussed. It is substantiated based on nannoplankton, dinocysts, foraminifers, and distinctive lithological features of deposits that the Oligocene-Miocene boundary is confined to the Alkun Formation at the Belaya River. 相似文献
9.
Stéphane Reboulet Peter F. Rawson Josep A. Moreno-Bedmar Maria B. Aguirre-Urreta Ricardo Barragán Yuri Bogomolov Miguel Company Celestina González-Arreola Vyara Idakieva Stoyanova Alexander Lukeneder Bertrand Matrion Vasily Mitta Hasina Randrianaly Zdenek Vaši?ek Evgenij J. Baraboshkin Didier Bert Stéphane Bersac Tamara N. Bogdanova Luc G. Bulot Jean-Louis Latil Irina A. Mikhailova Pierre Ropolo Ottilia Szives 《Cretaceous Research》2011,32(6):786-793
The 4th Kilian Group meeting (Dijon, France, 30th August 2010) focused on the Aptian and Albian Stages. For the Aptian, a two-fold division of the stage was adopted for the Mediterranean area with a boundary between the Dufrenoyia furcata and Epicheloniceras martini Zones. The main changes to the zonal scheme concern the Lower Aptian with: the introduction of a Deshayesites luppovi Subzone in the upper part of the Deshayesites oglanlensis Zone; the replacement of Deshayesites weissi by Deshayesites forbesi as new index-species of the second interval zone; the introduction of a Roloboceras hambrovi Subzone in the upper part of the D. forbesi Zone; and the subdivision of the D. furcata Zone into the D. furcata and Dufrenoyia dufrenoyi Subzones. For the Albian, the upper part of the Douvilleiceras mammillatum Zone (Lower Albian) is now characterized by a Lyelliceras pseudolyelli Subzone. The main amendments concern the Upper Albian. The base of this substage is defined by the base of the Dipoloceras cristatum Zone. Above it, the Upper Albian zonal scheme comprises in stratigraphic order the Mortoniceras pricei, Mortoniceras inflatum, Mortoniceras fallax, Mortoniceras rostratum, Mortoniceras perinflatum and Arrhaphoceras briacensis Zones. 相似文献
10.
N. K. Andreeva N. A. Kagramanyan T. N. Kheraskova 《Lithology and Mineral Resources》2000,35(4):373-389
New data on the stratigraphy and composition of the Devonian rocks of the Moscow Syneclise were used. Facies-paleogeographic
schemes were compiled for the Lochkovian, Eifelian, Givetian, early-middle Frasnian, late Frasnian, and early-late Famennian
evolutionary stages of the Moscow Syneclise. Seven sedimentation cycles were developed due to sealevel fluctuations and structural
rearrangements in the paleooceanic basins surrounding the East European Platform at that time. The inference was made on the
structural heterogeneity of the platform basement and on differentiated movements as well as on the strike-slip fault nature
of some fragments of the basement relative to each other in the Devonian. 相似文献