High-pressure neutron diffraction study on H–D isotope effects in brucite     

Juske Horita  António M. dos Santos  Christopher A. Tulk  Bryan C. Chakoumakos  Veniamin B. Polyakov 《Physics and Chemistry of Minerals》2010,37(10):741-749

A neutron powder diffraction study of hydrogenated and deuterated brucite was conducted at ambient temperature and at pressures up to 9 GPa, using a Paris–Edinburgh high-pressure cell at the WAND instrument of the ORNL High Flux Isotope Reactor. The two materials were synthesized by the same method and companion measurements of neutron diffraction were conducted under the same conditions. Our refinement results show that the lattice-parameters of the a axis, parallel to the sheets of Mg–O octahedra, decrease only slightly with pressure with no effect of H–D substitution. However, the c axis of Mg(OD)₂ is shorter and may exhibit greater compressibility with pressure than that of Mg(OH)₂. Consequently, the unit-cell volume of deuterated brucite is slightly, but systematically smaller than that of hydrogenated brucite. When fitted to a third-order Birch–Murnaghan equation in terms of the normalized unit-cell volume, values of the bulk modulus for hydrogenated and deuterated brucite (K ₀ = 39.0 ± 2.8 and 40.4 ± 1.3 GPa, respectively) are, however, indistinguishable from each other within the experimental errors. The measured effect of H–D substitution on the unit-cell volume also demonstrates that brucite (and other hydrous minerals) preferentially incorporate deuterium over hydrogen under pressure, suggesting that the distribution of hydrogen isotopes in deep-earth conditions may differ significantly from that in near-surface environments.  相似文献   

Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age,composition, sources,and geodynamic formation conditions     

Anh  Phan Luu  Vladimirov  A. G.  Kruk  N. N.  Polyakov  G. V.  Ponomarchuk  V. A.  Hoa  Tran Trong  Phuong  Ngo Thi  Kuibida  M. L.  Annikova  I. Yu.  Pavlova  G. G.  Kiseleva  V. Yu. 《Doklady Earth Sciences》2010,432(2):839-845

Doklady Earth Sciences - Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous...  相似文献   

The Ureg Nuur Pt-bearing volcanoplutonic picrite–basalt association in the Mongolian Altay as evidence for a Cambrian–Ordovician Large Igneous Province     

A.E. Izokh  A.V. Vishnevskii  G.V. Polyakov  V.M. Kalugin  T. Oyunchimeg  R.A. Shelepaev  V.V. Egorova 《Russian Geology and Geophysics》2010,51(5):521-533

The paper discusses geological, mineralogical, petrographic, and geochemical data on the Ureg Nuur volcanoplutonic association of high-Mg volcanic and subvolcanic rocks located among Vendian–Cambrian accretionary structures in the Mongolian Altay. These rocks have a high potassium alkalinity (K₂O/Na₂O up to 1.2), are enriched in LILE and Sr, and have negative Zr–Hf and Nb anomalies in multielement spectra; this confirms the suprasubduction type of the source of melts. The geological setting and established age (512.4 ± 6.1 Ma, ³⁹Ar–⁴⁰Ar dating of biotite phenocrysts) evidence picritic magmatism at the accretionary stage of the development of the Altay fragment of the Paleoasian ocean. This indicates a large igneous province related to a mantle plume.  相似文献   

North Atlantic warming: patterns of long-term trend and multidecadal variability   总被引：1，自引：1，他引：0  

Igor V. Polyakov  Vladimir A. Alexeev  Uma S. Bhatt  Evgenia I. Polyakova  Xiangdong Zhang 《Climate Dynamics》2010,34(2-3):439-457

Climate fluctuations in the North Atlantic Ocean have wide-spread implications for Europe, Africa, and the Americas. This study assesses the relative contribution of the long-term trend and variability of North Atlantic warming using EOF analysis of deep-ocean and near-surface observations. Our analysis demonstrates that the recent warming over the North Atlantic is linked to both long-term (including anthropogenic and natural) climate change and multidecadal variability (MDV, ~50–80 years). Our results suggest a general warming trend of 0.031 ± 0.006°C/decade in the upper 2,000 m North Atlantic over the last 80 years of the twentieth century, although during this time there are periods in which short-term trends were strongly amplified by MDV. For example, MDV accounts for ~60% of North Atlantic warming since 1970. The single-sign basin-scale pattern of MDV with prolonged periods of warming (cooling) in the upper ocean layer and opposite tendency in the lower layer is evident from observations. This pattern is associated with a slowdown (enhancement) of the North Atlantic thermohaline overturning circulation during negative (positive) MDV phases. In contrast, the long-term trend exhibits warming in tropical and mid-latitude North Atlantic and a pattern of cooling in regions associated with major northward heat transports, consistent with a slowdown of the North Atlantic circulation as evident from observations and confirmed by selected modeling results. This localized cooling has been masked in recent decades by warming during the positive phase of MDV. Finally, since the North Atlantic Ocean plays a crucial role in establishing and regulating the global thermohaline circulation, the multidecadal fluctuations discussed here should be considered when assessing long-term climate change and variability, both in the North Atlantic and at global scales.  相似文献   

Time variability of the total methane content in the atmosphere over the vicinity of St. Petersburg     

M. V. Makarova  A. V. Poberovskii  K. N. Visheratin  A. V. Polyakov 《Izvestiya Atmospheric and Oceanic Physics》2009,45(6):723-730

The results of measuring the methane content in the entire atmospheric thickness over the St. Petersburg region are given for 1991–2007. It is shown that, within this period, the mean annual cycle of the total methane content is characterized by its maximum values in December–January and its minimum values in June–August when the annual-cycle amplitude amounts to ∼3.6%. In this case, the annual variations in the total methane content may differ significantly from the mean annual cycle obtained in some years. A statistically significant linear trend of the total CH₄ content has not been revealed for 1991–2007. The obtained values of the linear-trend index have opposite signs in the winter and summer months (positive for January 0.6 ± 0.2%/year and February 0.4 ± 0.2%/year and negative for July 0.3 ± 0.2%/year and August 0.2 ± 0.1%/year). This fact suggests the tendency for an increase in the amplitude of the annual cycle of the total CH₄ content. The results of a spectral analysis of a series of data on the total CH₄ content show that, for 1991–2007, the following harmonics are pronounced with a confidence of 95%: 12 months (annual harmonic), 32 months (quasi-biennial oscillations), and 55 months (4.5 years), which are also pronounced in the series of meteorological parameters and total ozone content.  相似文献   

New data on seismostratigraphy and sedimentation on the western slope of the middle Caspian     

O. V. Levchenko  V. G. Gainanov  L. R. Merklin  A. S. Polyakov  A. G. Roslyakov 《Doklady Earth Sciences》2006,411(9):1366-1369

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Determination of tin equilibrium isotope fractionation factors from synchrotron radiation experiments     

V.B. Polyakov  S.D. Mineev  G. Hu 《Geochimica et cosmochimica acta》2005,69(23):5531-5536

A method of determination of the reduced isotopic partition function ratio (β-factor) from the partial density of state (PDOS) obtained by inelastic nuclear resonant X-ray scattering (INRXS) in synchrotron radiation experiments has been established. The method has been demonstrated by the example of tin isotopes. The tin β-factors for CaSnO₃, SnO₂, SnO have been computed from the INRXS-derived PDOSs.