Pressure-induced phase transition in Mg0.8Fe0.2O ferropericlase     

Innokenty Kantor  Leonid Dubrovinsky  Catherine McCammon  Anastasia Kantor  Sakura Pascarelli  Giuliana Aquilanti  Wilson Crichton  Maurizio Mattesini  Rajeev Ahuja  Jailton Almeida  Vadim Urusov 《Physics and Chemistry of Minerals》2006,33(1):35-44

Combined X-ray powder diffraction, Mössbauer, and XANES spectroscopy in situ experiments revealed the transformation of cubic (Mg_0.8Fe_0.2)O ferropericlase to a rhombohedrally distorted phase at 35(1) GPa and room temperature. The Mössbauer spectroscopy results show that the rhombohedral distortion does not involve magnetic ordering. Combined with data from the literature, our results imply that the cubic to rhombodedral transition occurs in (Mg,Fe)O under conditions of non-hydrostatic stress over a wide range of composition (0.2≤x _Fe≤1).  相似文献   

Immiscible silicate liquid partition coefficients: implications for crystal-melt element partitioning and basalt petrogenesis   总被引：2，自引：1，他引：2  

Ilya V. Veksler  Alexander M. Dorfman  Leonid V. Danyushevsky  Jakob K. Jakobsen  Donald B. Dingwell 《Contributions to Mineralogy and Petrology》2006,152(6):685-702

This study investigates partitioning of elements between immiscible aluminosilicate and borosilicate liquids using three synthetic mixtures doped with 32 trace elements. In order to get a good spatial separation of immiscible liquids, we employed a high-temperature centrifuge. Experiments were performed at 1,050–1,150°C, 1 atm, in sealed Fe and Pt containers. Quenched products were analysed by electron microprobe and LA ICP-MS. Nernst partition coefficients (D’s) between the Fe-rich and Si-rich aluminosilicate immiscible liquids are the highest for Zn (3.3) and Fe (2.6) and the lowest for Rb and K (0.4–0.5). The plots of D values against ionic potential Z/r in all the compositions show a convex upward trend, which is typical also for element partitioning between immiscible silicate and salt melts. The results bear upon the speciation and structural position of elements in multicomponent silicate liquids. The ferrobasalt–rhyolite liquid immiscibility is observed in evolved basaltic magmas, and may play an important role in large gabbroic intrusions, such as Skaergaard, and during the generation of unusual lavas, such as ferropicrites.  相似文献   

Origin of upper-mantle seismic scattering – evidence from Russian peaceful nuclear explosion data     

Lars Nielsen  Hans Thybo  Alan Levander  Leonid N. Solodilov 《Geophysical Journal International》2003,154(1):196-204

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峨眉火成岩省内带岩浆硫化物含矿岩体橄榄石的成因意义     

官建祥  宋谢炎  陈列锰  聂晓勇 《矿物岩石地球化学通报》2008,27(Z1)

岩浆镍-铜-铂族元素(PGE)硫化物矿床是峨眉火成岩省地幔柱活动形成的两个重要的成矿系列之一[1～3].目前已发现的与峨眉火成岩省相关的40余个镍-铜-铂族元素硫化物矿床(或矿点)中,多数分布在内带[3,4].它们可分为:1)富Ni、Cu而贫PGE的Ni-Cu型(如力马河和清水河);2)富Ni,Cu且PGE中等的Ni-Cu-PGE型(如清矿山和黄草坪);3)贫Ni、Cu富PGE的PGE型(如金宝山和杨合武).  相似文献   

Parameters of the Infrasound Signal Generated by a Meteoroid over Indonesia on October 8, 2009     

L.?F.?ChernogorEmail author  M.?B.?Shevelev 《Kinematics and Physics of Celestial Bodies》2018,34(3):147-160

The basic parameters (delay time, celerity, duration, oscillation period, and amplitude) of the infrasound signal recorded by 17 stations are statistically analyzed as a function of the horizontal distance between the Indonesian superbolide total radiated energy and the infrasound station location. Fitting dependences of signal parameters on distance are given. Correlation diagrams are constructed and analyzed. The basic parameters of the meteoroid, the corrected value of the infrasound signal celerity, and the average tropospheric-stratospheric wind velocity are estimated.  相似文献   

Precise geodesy with the Very Long Baseline Array   总被引：2，自引：2，他引：0  

Leonid Petrov  David Gordon  John Gipson  Dan MacMillan  Chopo Ma  Ed Fomalont  R. Craig Walker  Claudia Carabajal 《Journal of Geodesy》2009,83(9):859-876

We report on a program of geodetic measurements between 1994 and 2007 which used the Very Long Baseline Array (VLBA) and up to ten globally distributed antennas. One of the goals of this program was to monitor positions of the array at a 1 mm level of accuracy and to tie the VLBA into the international terrestrial reference frame. We describe the analysis of these data and report several interesting geophysical results including measured station displacements due to crustal motion, earthquakes, and antenna tilt. In terms of both formal errors and observed scatter, these sessions are among the very best geodetic very long baseline interferometry experiments.  相似文献   

Phase transition in CaSiO₃ perovskite     

Tetsuya Komabayashi  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi  Leonid S. Dubrovinsky 《Earth and Planetary Science Letters》2007,260(3-4):564-569

A phase transition in pure CaSiO₃ perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO₃ perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT / dP slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al₂O₃ content dissolved in CaSiO₃ perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO₃(+ 3 wt.% Al₂O₃) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range.  相似文献   

Stratigraphic constraints on late Pleistocene glacial erosion and deglaciation of the Chukchi margin, Arctic Ocean   总被引：2，自引：0，他引：2  

Leonid Polyak  Dennis A. Darby  Martin Jakobsson 《Quaternary Research》2007,67(2):234-245

At least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ¹⁸O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ¹⁸O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.  相似文献   

On stochastic stability of regional ocean models to finite-amplitude perturbations of initial conditions   总被引：1，自引：0，他引：1  

Leonid M. Ivanov  Peter C. Chu 《Dynamics of Atmospheres and Oceans》2007,43(3-4):199-225

We consider error propagation near an unstable equilibrium state (classified as an unstable focus) for spatially uncorrelated and correlated finite-amplitude initial perturbations using short- (up to several weeks) and intermediate (up to 2 months) range forecast ensembles produced by a barotropic regional ocean model. An ensemble of initial perturbations is generated by the Latin Hypercube design strategy, and its optimal size is estimated through the Kullback–Liebler distance (the relative entropy). Although the ocean model is simple, the prediction error (PE) demonstrates non-trivial behavior similar to that existing in 3D ocean circulation models. In particular, in the limit of zero horizontal viscosity, the PE at first decays with time for all scales due to dissipation caused by non-linear bottom friction, and then grows faster than (quasi)-exponentially. Statistics of a prediction time scale (the irreversible predictability time (IPT)) quickly depart from Gaussian (the linear predictability regime) and becomes Weibullian (the non-linear predictability regime) as amplitude of initial perturbations grows. A transition from linear to non-linear predictability is clearly detected by the specific behavior of IPT variance. A new analytical formula for the model predictability horizon is introduced and applied to estimate the limit of predictability for the ocean model.  相似文献   

Uranium Concentration in Altered Brown Coals Located under Burnt Rocks from the Kansk-Achinsk Basin, West Siberia     

Vsevolod M. Gavshin  Leonid V. Miroshnichenko 《Geostandards and Geoanalytical Research》2000,24(2):241-246

West Siberian brown coals from the Kansk-Achinsk basin and their combustion products are generally characterized by a low uranium content. In some places where brown coal has been altered (losing density, becoming cracked or friable), the uranium content has increased by concentrations ranging from 1001000 μg g⁻¹. At these locations distinct signs of underground fires are visible. The uranium distribution patterns suggest that the burnt organic matter was a source of uranium and altered varieties of coal serve as a geochemical barrier to uranium transport.  相似文献