Evolutionary Processes in Anthropogenic Biogeochemical Provinces     

T. I. Moiseenko 《Geochemistry International》2018,56(10):982-991

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N–C–Ar–He Isotopic Systematics of Quenched Tholeiitic Glasses from the Bouvet Triple Junction Area     

A. I. Buikin  A. B. Verchovsky  N. A. Migdisova 《Geochemistry International》2018,56(13):1368-1383

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Composition,Structure, and Conditions of Formation of Fluorine-Bearing Sodalite: Experimental Evidence     

E. N. Gramenitskii  A. R. Kotel’nikov  T. I. Shchekina  O. V. Yakubovich  V. N. Devyatova  E. S. Zubkov  N. I. Suk  M. F. Vigasina  Z. A. Kotel’nikova 《Geochemistry International》2018,56(6):521-534

Fluoro-sodalite was synthesized for the first time at temperatures of 400–800°C and H₂O pressures of 1–2 kbar in the Si–Al–Na–H–O–F system. X-ray diffraction and infrared spectroscopic investigations showed that fluorine is incorporated in the sodalite structure as anionic octahedral groups, [AlF₆]^3–, the number of which can vary from 0 to 1. Correspondingly, the end-members of the F-sodalite series are Na₇(H₂O)₈[Si₅Al₇O₂₄] and Na₈(AlF₆)(H₂O)₄[Si₇Al₅O₂₄]. Depending on the composition of the system, F-sodalite associates at 500–650°C with nepheline, albite, cryolite, and villiaumite, which are joined by analcime below 500°C and aluminosilicate melt above 650°C. Fluorine-bearing sulfate–chlorine-sodalite was found for the first time in a pegmatite sample from the Lovozero massif. The highest fraction of the fluorine end-member in natural sodalite is 0.2. The incorporation of F into the sodalite structure requires much more energy compared with Cl^– and SO ₄ ^2- , because it is accompanied by a structural rearrangement and a transition from tetrahedral Al to octahedral Al.  相似文献   

Geochemistry,Tectonic Settings,and Age of Metavolcanic Rocks of the Isakovskii Terrane,Yenisei Range: Indicators of the Early Evolution of the Paleo-Asian Ocean     

I. I. Likhanov  A. D. Nozhkin 《Geochemistry International》2018,56(4):292-303

The geodynamic nature of the Late Neoproterozoic island-arc dacites (691 ± 8.8 Ma) and rift basalts (572 ± 6.5 Ma) of the Kiselikhinskaya Formation, Kutukasskaya Group, in the Isakovskii terrane is inferred from geochemical data and U–Pb zircon (SHRIMP-II) dates. The volcanic rocks were produced during the late evolutionary history of the Yenisei Range, starting at the origin of oceanic crustal fragments and their accretion to the Siberian craton to the postaccretionary crustal extension and the onset of the Caledonian orogenesis. The reproduced sequence of geological processes marks the early evolution of the Paleo- Asian Ocean in its junction zone with the Siberian craton. The data refine the composition and age of volcanic rocks in the trans-Angara part of the Yenisei Range and specifics of the Neoproterozoic evolution of the Sayan–Yenisei accretionary belt.  相似文献   

Mercury in Hydrobionts and Their Habitat in Grønfjorden,West Spitsbergen,in Early Springtime     

N. V. Lebedeva  O. L. Zimina  N. N. Fateev  A. L. Nikulina  I. V. Berchenko  N. I. Meshcheryakov 《Geochemistry International》2018,56(4):332-343

The first data were obtained on the total mercury content in hydrobionts and their habitat in Grønfjorden, Spitsbergen, at the waste discharge sites of the settlement of Barentsburg in early spring 2017. The Hg concentration was below the detection limit in the water and varied from 7.1 to 42.3 ng/g of dry weight in the bottom sediments. Mercury concentration in the hydrobionts increased toward the inner fjord and was higher near the mouth of the Grøndalen River, which flows into the fjord. Elevated Hg concentrations at the mouth of the Grøndalen River indicate that much of the toxic metal is brought to the inner part of the fjord with riverine runoff, and this Hg source is likely more important than the surface supply of Hg transferred from local surface pollution centers at Barentsburg. The Hg concentration depended on the position of the marine organisms in the trophic chain and was the highest in the detritophage mollusks Thyasira gouldi, Cardium sp., and Macoma calcarea, the specialized predatory sea snail Cryptonatica affinis, and the cod Gadus morhua, which is a benthosophage–secondary predator. The total Hg concentrations in the hydrobionts and their habitat in Grønfjorden were generally relatively low and close to the background one.  相似文献   

Crystal nucleation and growth produced by continuous decompression of Pinatubo magma     

Kenneth?S.?BefusEmail author  Benjamin?J.?Andrews 《Contributions to Mineralogy and Petrology》2018,173(11):92

High-temperature decompression experiments demonstrate that crystal textures preserve a record of the style and rate of magmatic ascent. To reinforce this link, we performed a suite of isothermal decompression experiments using starting material from the climactic 1991 Pinatubo eruption. We decompressed experiments from 220 MPa to final, quench pressures of 75 or 30 MPa using continuous decompression rates of 100, 30, 10, 3, 1, and 0.3 MPa h^?1. Amphibole, clinopyroxene, and plagioclase crystallized during the experiments, with plagioclase microlites dominating the assemblage. Total microlite number densities range from 10^7.6±0.4 up to 10^8.2±0.2 cm^?3, with plagioclase accounting for up to 65% of the total number. Plagioclase microlite area increased systematically from 19?±?8 to 937?±?487 µm² with increasing experiment duration. Our textures provide time-integrated records of crystal kinetics. Average nucleation and areal growth rates of plagioclase are highest in the fastest decompressions (~?10^7.5 cm^?3 h^?1 and 10.1?±?4.1 µm² h^?1, respectively) and more than an order of magnitude lower in the slowest experiments (~?10^5.5 cm^?3 h^?1 and 0.8?±?0.2 µm² h^?1, respectively). Both nucleation and growth rates are highest at high degrees of disequilibrium. We find that peak supersaturation-dependent instantaneous rates are generally more than an order of magnitude faster than average rates. We use those instantaneous nucleation and growth rates to introduce an iterative model to evaluate the effects of different decompression rates, decompression paths (continuous, single-step or multistep), and the presence of phenocrysts on final crystallinity and microlite size distribution.  相似文献   

Deformations and Structural Evolution of Mesozoic Complexes in Western Chukotka     

B. G. Golionko  E. V. Vatrushkina  V. E. Verzhbitskii  S. D. Sokolov  M. I. Tuchkova 《Geotectonics》2018,52(1):56-72

Detailed structural investigations have been carried out in the Pevek district to specify tectonic evolution of the Chukotka mesozoids. The earliest south-verging folds F1 formed in Triassic rocks at the first deformation stage DI. These structures are overlapped by the northern-verging folds F₂ and overthrusts pertain to the second deformation stage DII. Folding structures F₁ and F₂ were deformed by shear folds F₃, completing stage DII. The DI and DII structures are complicated by roughly NS-trending normal faults marking deformation stage DIII. It has been established that DI is related to the onset of opening of the Amerasian Basin in the Early Jurassic, or, alternatively, to the later accretion of the Kulpolnei ensimatic arc toward the Chukotka microcontinent. DII marks the collision of Siberia and the Chukotka microcontinent in the Late Neocomian. Normal faulting under the roughly E–W-trending extension during DIII is likely related to rift opening of the Podvodnikov and Makarov–Toll basins in the deep Amerasian Basin. Formation of the Okhotsk–Chukotka volcanoplutonic belt completed the structural evolution of the studied region.  相似文献   

Phosphides in Volcanic Seamount Basalts in the Sea of Japan     

V. T. S”edin  O. N. Kolesnik  E. I. Yaroshchuk 《Lithology and Mineral Resources》2018,53(4):324-328

Electron microprobe data on phosphide grains detected for the first time in basalts from volcanic edifices in the Sea of Japan are presented. The find of phosphides can testify to the endogenic source of phosphorus and, consequently, volcanogenic hydrothermal origin of phosphorites in the Sea of Japan.  相似文献   

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)     

Emily Keeble  David I. Whiteside  Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):99-119

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.  相似文献   

A Kinematic Model of the Formation of the Sim Trough of the Uralian Foredeep     

Al. V. Tevelev  I. A. Prudnikov  Ark. V. Tevelev  A. O. Khotylev  E. A. Volodina 《Moscow University Geology Bulletin》2018,73(3):238-246

The structural features and mechanism of the formation of the Sim trough within the Uralian Foredeep, as well as the development of the entire Karatau–Suleiman block, are considered. This wedge-shaped block was subject to lateral extrusion to the north along conjugated strike-slip fault zones under a general latitudinal compression. This factor determined the local meridional compression and latitudinal extension of the block. In the central part of the block, the latitudinal extension was compensated by gradual subsidence, which resulted in the formation of the Sim trough.  相似文献