Geodynamics of the Barents–Kara margin in the Mesozoic inferred from paleomagnetic data on rocks from the Franz Josef Land Archipelago     

N. E. Mikhaltsov  Yu. V. Karyakin  V. V. Abashev  V. Yu. Bragin  V. A. Vernikovsky  A. V. Travin 《Doklady Earth Sciences》2016,471(2):1242-1246

New data on paleomagnetism and isotope geochronology of Jurassic and Early Cretaceous basic igneous rocks on Franz Josef Land Archipelago (FJL) represented by flows and dikes are discussed. The first paleomagnetic data obtained for these rocks offer the opportunity to suggest a model of spatial changes in the FJL block position during the Jurassic?Cretaceous. In the Early Jurassic, the block occupied a different position relative to Europe from the modern one. It was displaced in the northeasterly direction by a distance of approximately 500 km and rotated clockwise by about 40° relative to its modern position. By the Early Cretaceous, the FJL block occupied a position close to the present-day one avoiding subsequent substantial relative displacements. The data obtained are of principal significance for reconstructing the geodynamic evolution of Arctic structures in the Mesozoic and contribute greatly to the base of paleomagnetic data for the Arctic region, development of which is now in progress.  相似文献   

Disseminated gold–sulfide mineralization at the Zhaima deposit,eastern Kazakhstan     

K. R. Kovalev  O. N. Kuzmina  B. A. Dyachkov  A. G. Vladimirov  Yu. A. Kalinin  E. A. Naumov  M. V. Kirillov  I. Yu. Annikova 《Geology of Ore Deposits》2016,58(2):116-133

The Zhaima gold–sulfide deposit is located in the northwestern part of the West Kalba gold belt in eastern Kazakhstan. The mineralization is hosted in Lower Carboniferous volcanic and carbonate rocks formed under conditions of marginal-sea and island-arc volcanic activity. The paper considers the mineralogy and geochemistry of primary gold–sulfide ore and Au-bearing weathering crusts. Au-bearing arsenopyrite–pyrite mineralization formed during only one productive stage. Disseminated, stringer–disseminated, and massive rocks are enriched in Ti, Cr, V, Cu, and Ni, which correspond to the mafic profile of basement. The main ores minerals are represented by finely acicular arsenopyrite containing Au (up to few tens of ppm) and cubic and pentagonal dodecahedral pyrite with sporadic submicroscopic inclusions of native gold. The sulfur isotopic composition of sulfides is close to that of the meteoritic standard (δ³⁴S =–0.2 to +0.2). The ⁴⁰Ar/³⁹Ar age of three sericite samples from ore veinlets corresponds to the Early Permian: 279 ± 3.3, 275.6 ± 2.9, and 272.2 ± 2.9 Ma. The mantle source of sulfur, ore geochemistry, and spatial compatibility of mineralization with basic dikes allow us to speak about the existence of deep fluid–magmatic systems apparently conjugate with the Tarim plume.  相似文献   

Deposition conditions and distribution features of native gold individuals in the veins of the Tokur mesothermal deposit,Russia     

N. S. Ostapenko  O. N. Neroda 《Geology of Ore Deposits》2016,58(3):213-223

The paper discusses factors in the deposition and concentration of native gold and the spatial distribution of its individuals within the sufide-poor gold–quartz veins at the mesoabyssal Tokur deposit. The major factors in deposition of gold were sealing of the hydrothermal system, a sudden drop in fluid pressure, and repeated immiscibility in the fluid. Native gold was deposited in relation to initial acts of prolonged and discrete opening and preopening of cavities in three mineral assemblages of the productive association II. Most native gold individuals with a visible size of 0.1–1.5 mm were together with the early generation of quartz 2 on cavity walls adjacent to altered rocks. This is caused by the high content of Au complexes in initial hydrothermal solutions favoring rapid oversaturation during cavity formation. Gold fills interstices between grains of quartz 2 throughout the deposit and mineral assemblages. The vertical-flow distribution of gold has been established in economic veins; the upper and middle levels are enriched in gold, and samples with the greatest gold grade of 100–500 g/t or higher are concentrated there. This is caused both by the predominance of mineral association II at these levels and probable natural flotation of gold grains contained in the gold–gas associate for immiscibility of the hydrothermal fluid at the second stage of the ore-forming process.  相似文献   

Geology and mineralogy of the Alakha spodumene granite porphyry deposit,Gorny Altai,Russia     

I. Yu. Annikova  A. G. Vladimirov  S. Z. Smirnov  O. A. Gavryushkina 《Geology of Ore Deposits》2016,58(5):404-426

The Alakha lithium–tantalum deposit in the southern Altai, Russia, is represented by a stock of spodumene-bearing granite porphyry localized in the Kalba–Narym–Koktogai lithium–tantalum rare-metal granitic belt, unique in extent (more than 1000 km). This belt is a part of the Altai accretionary–collisional system. Judging from forecasting, the Alakha deposit can be regarded as an uneroded proxy of a pegmatite body both in dimensions and mean Li₂O and Ta₂O₅ contents (0.98 wt % and 114 ppm, respectively); however, the oregenerating potential of this deposit remains insufficiently studied and had not yet been claimed. In this paper, we attempt to fill this gap with a detailed mineralogical study, which allows us to provide insights into the crystallization of Li-bearing high-silicic magma and redistribution of components during magmatic and postmagmatic processes. Accessory mineral assemblages in muscovite–spodumene–K-feldspar granite porphyry and muscovite albitite—the main petrographic rock varieties of the Alakha stock—turned out to be almost identical. A significant similarity in the chemistry of major rock-forming minerals is established for spodumene granite porphyry of the Alakha stock and spodumene pegmatites from large deposits, which makes it possible to suggest that they are close in the petrogenetic mechanism of their formation. The mineral assemblages of muscovite albitite in the apical portion of the Alakha stock are connected by gradual transition with those of spodumene granite porphyry. Such a transition is caused by postmagmatic metasomatic alteration of the latter.  相似文献   

IR photometry and models for the dust envelopes of two carbon stars     

M. B. Bogdanov  O. G. Taranova 《Astronomy Reports》2016,60(12):1046-1051

The results of JHKLM photometry of two carbon stars are presented: the irregular variable NQ Cas and the Mira star BD Vul. Data on the mean fluxes supplemented with mid-IR observations with the IRAS, AKARI, andWISE satellites are used to compute spherically symmetrical model dust envelopes for the stars, consisting of particles of amorphous carbon and silicon carbide. The optical depth in the visible for the comparatively cool dust envelope of BD Vul, with a dust temperature at its inner boundary T₁ = 610 K, is fairly low: τ_V = 0.13. The dust envelope of NQ Cas is appreciably hotter (T₁ = 1550 K), and has τ_V = 0.32. The estimated mass-loss rates are 1.5 × 10^?7M_⊙/yr for NQ Cas and 5.9 × 10^?7M_⊙/yr for BD Vul.  相似文献   

The total number of spicules on the solar surface and their role in heating and mass balanace in the solar corona     

S. G. Mamedov  D. M. Kuli-Zade  Z. F. Alieva  M. M. Musaev  F. R. Mustafa 《Astronomy Reports》2016,60(9):848-852

A critical review of determinations of the number of spicules is presented, and the role of both classical and Type 2 spicules in heating and mass balance in the corona is considered. The total number of Type 2 spicules is determined, together with the upward fluxes of energy and mass to which they give rise. The total number of Type 2 spicules on the solar surface is found to be ~10⁵, close to values obtained in other studies. The associated particle flux toward the corona is 2.5 × 10¹⁴ cm^?2 s^?1, an order of magnitude lower than the corresponding flux for classical spicules. The associated energy flux is 10⁴ erg cm^?2 s^?1, an order of magnaitude lower than estimates obtained in other studies. The results indicate that Type 2 spicules can supply the mass lost from the corona, but are not able to fully explain coronal energy losses.  相似文献   

A Tribute to Thomas M. Church: Exploring Chemical Oceanography in the Coastal Zone—The History and Future     

Gregory A. Cutter  David J. Burdige 《Aquatic Geochemistry》2016,22(4):271-274

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Direct and Indirect Effects of Estuarine Reclamation on Nutrient and Metal Fluxes in the Global Coastal Zone   总被引：1，自引：1，他引：0  

T. D. Jickells  J. E. Andrews  D. J. Parkes 《Aquatic Geochemistry》2016,22(4):337-348

We demonstrate that land reclamation in estuaries is resulting in very large-scale loss of intertidal area and disconnection of stored sediment with the water column. This process is not just causing loss of estuarine ecosystem services, it is also having a major deleterious impact on the ability of estuaries to retain nutrients and trace metals. The global scale of loss of estuarine wetlands and subtidal sediments has reached the point where the impact of this loss of estuarine retention is likely to be affecting coastal seas worldwide and possibly global element cycles.  相似文献   

Marine Chemistry in the Coastal Environment: Principles,Perspective and Prospectus   总被引：1，自引：1，他引：0  

Thomas M. Church 《Aquatic Geochemistry》2016,22(4):375-389

Marine chemistry of the coastal environment starts with principles of rock weathering that use carbonic acid to mobilize elements, only some of which comprise the majority of sea salt. The principle reason is reverse weathering, extensively represented in coastal waters, and returns most elements to newly formed colloids or minerals while recycling carbon dioxide to the atmosphere. This includes the deeper ocean expanse of sediment diagenesis, plus hydrothermal plumes and attendant low-temperature basalt alteration. Within the estuarine and extended shelf regimes, both conservative and non-conservative processes can be distinguished and modeled to determine proportions of weathered elements transmitted to the sea or consumed by reverse weathering. Conceptually, the steady-state processes that lead to the composition of seawater can be viewed as heterogeneous equilibria between dissolved constituents and solid mineral products taking hundreds of millennia. However, initial processes in the estuarine and coastal environment are characterized by shorter term scavenging associated with inorganic and organic colloids. These recycle both carbon and trace elements on timescales commensurate with estuarine flushing and coastal exchange with the ocean. The natural uranium and thorium decay series provide powerful tools for quantifying the rates of estuarine processes, including those within groundwater and the subterranean estuary. In the future, new mass spectrometric and nuclear magnetic resonance techniques will help to define the molecular nature of newly formed estuarine colloids as has been done for dissolved organic matter. As the coastal environment undergoes the forces of climate change in the form of warming and sea level rise, future research should address how these will impact chemistry of the coastal environment as a net source or sink of carbon dioxide and associated organic material.  相似文献   

Impacts of a large Sahelian city on groundwater hydrodynamics and quality: example of Niamey (Niger)     

Aïssata B. Hassane  Christian Leduc  Guillaume Favreau  Barbara A. Bekins  Thomas Margueron 《Hydrogeology Journal》2016,24(2):407-423

The management of groundwater resources is very important in the semiarid Sahel region, which is experiencing rapid urban development. Impacts of urbanization on groundwater resources were investigated in the unconfined aquifer of the Continental Terminal beneath the city of Niamey, Niger, using water level and chemical data. Hydrodynamic and chemical changes are best described by a combination of factors including the historical development of the city, current land use, water-table depth and topography. Seasonal groundwater recharge occurs with high spatial variability, as indicated by water-level monitoring in all wells, but there was no interannual trend over the 5-year study period. Groundwater salinity shows high spatial variability and a minor rising trend. The highest salinity is in the old city centre, with Na–NO₃ dominant, and it increases seasonally with recharge. Salinity is much lower and more variable in the suburbs (Ca–HCO₃, Ca–NO₃, and Na–NO₃ dominant). Nitrate is the main ionic contaminant and is seasonally or permanently above the international guidelines for drinking water quality in 36 % of sampled wells, with a peak value of 112 mg L^?1 NO₃–N (8 meq L^?1). Comparison of urban and rural sites indicates a long-term increase in groundwater recharge and nitrate enrichment in the urban area with serious implications for groundwater management in the region.  相似文献