Mineralogy, composition and PGM of chromitites from Pefki, Pindos ophiolite complex (NW Greece): evidence for progressively elevated fAs conditions in the upper mantle sequence     

Argirios Kapsiotis  Tassos A. Grammatikopoulos  Basilios Tsikouras  Konstantin Hatzipanagiotou  Federica Zaccarini  Giorgio Garuti 《Mineralogy and Petrology》2011,101(1-2):129-150

The Pindos ophiolite complex, located in the northwestern part of continental Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. The Pefki chromitites are banded and sub-concordant to the surrounding serpentinized dunites. The Cr# [Cr/(Cr?+?Al)] of magnesiochromite varies between 0.75 and 0.79. The total PGE grade ranges from 105.9 up to 300.0?ppb. IPGE are higher than PPGE, typical of mantle hosted ophiolitic chromitites. The PGM assemblage in chromitites comprises anduoite, ruarsite, laurite, irarsite, sperrylite, hollingworthite, Os-Ru-Ir alloys including osmium and rutheniridosmine, Ru-bearing oxides, braggite, paolovite, platarsite, cooperite, vysotskite, and palladodymite. Iridarsenite and omeiite were also observed as exsolutions in other PGM. Rare electrum and native Ag are recovered in concentrates. This PGM assemblage is of great petrogenetic importance because it is significantly different from that commonly observed in podiform mantle-hosted and banded crustal-hosted ophiolitic chromitites. PGE chalcogenides of As and S are primary, and possibly crystallized directly from a progressively enriched in As boninitic melt before or during magnesiochromite precipitation. The presence of Ru-bearing oxides implies simultaneous desulfurization and dearsenication processes. Chemically zoned laurite and composite paolovite-electrum intergrowths are indicative of the relatively high mobility of certain PGE at low temperatures under locally oxidizing conditions. The PGM assemblage and chemistry, in conjunction with geological and petrologic data of the studied chromitites, indicate that it is characteristic of chromitites found within or close to the petrologic Moho. Furthermore, the strikingly different PGM assemblages between the high-Cr chromitites within the Pindos massif is suggestive of non-homogeneous group of ores.  相似文献   

Petrographic Investigation of Microcrack Initiation in Mafic Ophiolitic Rocks Under Uniaxial Compression     

Ioannis Rigopoulos  Basilios Tsikouras  Panagiotis Pomonis  Konstantin Hatzipanagiotou 《Rock Mechanics and Rock Engineering》2013,46(5):1061-1072

This paper investigates the influence of the petrographic characteristics of mafic ophiolitic rocks on the initiation and propagation of microcracks during uniaxial compression. The microcrack patterns of a troctolite and a diorite, collected from the Pindos and Othrys ophiolites (Greece), respectively, were analysed. Thorough observation and quantification of microcracks before and after the uniaxial compression test were conducted. Combined fluorescent and polarised microscopy of polished thin sections, together with digital image analysis, indicated that the intragranular microcracks are the dominating crack type in both loaded and unloaded specimens, only in terms of their total number and length. On the other hand, the intergranular and transgranular cracks seem to grow more readily compared to the intragranular cracks, implying that the longer microcracks grow more extensively under stress. The orientation of most of the newly formed intragranular and transgranular microcracks is nearly parallel to the loading direction; however, some of the randomly oriented transgranular cracks have probably been formed during the propagation of intergranular cracks. In the troctolite, the frequency of the intragranular microcracks decreases in the olivine crystals after the uniaxial compression test due to their partial serpentinisation, which increases their resistance to brittle deformation. In the plagioclase crystals of the troctolite, microcracks are often oriented parallel to the cleavage planes, implying that such crystallographic orientations act as planes of weakness. On the contrary, the plagioclase crystals of the diorite are mainly crossed by randomly oriented microcracks, presumably due to their high degree of alteration. In the diorite, the evolution of microcracks is substantially controlled by the two perfect cleavages of amphibole. The failure of a rock occurs as a result of the growth, interaction and coalescence of a great number of pre-existing and newly formed intragranular and transgranular microcracks. The petrographic and microcrack analysis may assist in the selection of the most suitable rock type for various construction applications.  相似文献   

Finite volume approximation for an immiscible two-phase flow in porous media with discontinuous capillary pressure     

Konstantin Brenner  Clément Cancès  Danielle Hilhorst 《Computational Geosciences》2013,17(3):573-597

We consider an immiscible incompressible two-phase flow in a porous medium composed of two different rocks so that the capillary pressure field is discontinuous at the interface between the rocks. This leads us to apply a concept of multivalued phase pressures and a notion of weak solution for the flow which have been introduced in Cancès and Pierre (SIAM J Math Anal 44(2):966–992, 2012). We discretize the problem by means of a numerical algorithm which reduces to a standard finite volume scheme in each rock and prove the convergence of the approximate solution to a weak solution of the two-phase flow problem. The numerical experiments show in particular that this scheme permits to reproduce the oil-trapping phenomenon.  相似文献   

Dust torus formed by particles ejected from a celestial body at an arbitrary point of its elliptic orbit     

Sergei A. Orlov  Konstantin V. Kholshevnikov 《Celestial Mechanics and Dynamical Astronomy》2013,116(1):35-52

Dust comnplexes make one of the components of the Solar System. The surface shape of a typical dust complex consisting of particles ejected by a celestial body is found analytically, under reasonable assumptions (the main one being the smallness of perturbations). Parametric equations of the surface are obtained. The main properties of the surface are established and studied. Singular points are found, and the topological type of the surface as a whole and in the vicinity of the singular points (one conic points and one constriction) is examined.  相似文献   

Glacial isostatic adjustment in 3-D earth models: Implications for the analysis of tide gauge records along the U.S. east coast     

Jonathan E. Davis  Konstantin Latychev  Jerry X. Mitrovica  Roblyn Kendall  Mark E. Tamisiea 《Journal of Geodynamics》2008,46(3-5):90

Tide gauge records of recent sea-level change along the U.S. east coast have received significant attention within the literature of glacial isostatic adjustment (GIA). Geographic trends in these tide gauge rates are not reduced by a GIA correction based on a commonly adopted radial viscosity profile (characterized, in particular, by a lower mantle viscosity 1−2×10²¹ Pa s), and this has led to speculation that the residual trends reflect contributions from neotectonics or oceanographic processes. While the trends can be significantly reduced by adopting an Earth model with a stiffer lower mantle, such a model appears to be incompatible with independent constraints from post-glacial decay times in Hudson Bay. We use a finite-element model of the GIA process to investigate whether 3-D viscosity variations superimposed onto the “common” radial viscosity profile may provide a route to reconciling the east coast sea-level trends. We find that the specific 3-D structure we impose has little impact on the geographic trends in the GIA-corrected rates. However, we do find that the imposed lateral variations in lower mantle viscosity introduce a nearly uniform upward shift of 0.5 mm/yr in GIA-induced sea-level rates along the U.S. east coast. Thus, inferences of regional (U.S. east coast) sea-level rise due to modern melting of ice reservoirs, based on tide gauge rates corrected using 1-D GIA models, may be significantly biased by this simplifying assumption.  相似文献   

Thermal equation of state of magnesite to 32 GPa and 2073 K     

Konstantin D. Litasov  Yingwei Fei  Eiji Ohtani  Takahiro Kuribayashi  Kenichi Funakoshi 《Physics of the Earth and Planetary Interiors》2008,168(3-4):191-203

Pressure–volume–temperature relations have been measured to 32 GPa and 2073 K for natural magnesite (Mg_0.975Fe_0.015Mn_0.006Ca_0.004CO₃) using synchrotron X-ray diffraction with a multianvil apparatus at the SPring-8 facility. A least-squares fit of the room-temperature compression data to a third-order Birch–Murnaghan equation of state (EOS) yielded K₀ = 97.1 ± 0.5 GPa and K′ = 5.44 ± 0.07, with fixed V₀ = 279.55 ± 0.02 Å³. Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (∂K_T/∂T)_P = −0.013 ± 0.001 GPa/K and zero-pressure thermal expansion α = a₀ + a₁T with a₀ = 4.03 (7) × 10⁻⁵ K⁻¹ and a₁ = 0.49 (10) × 10⁻⁸ K⁻². The Anderson–Grüneisen parameter is estimated to be δ_T = 3.3. The analysis of axial compressibility and thermal expansivity indicates that the c-axis is over three times more compressible (K_Tc = 47 ± 1 GPa) than the a-axis (K_Tc = 157 ± 1 GPa), whereas the thermal expansion of the c-axis (a₀ = 6.8 (2) × 10⁻⁵ K⁻¹ and a₁ = 2.2 (4) × 10⁻⁸ K⁻²) is greater than that of the a-axis (a₀ = 2.7 (4) × 10⁻⁵ K⁻¹ and a₁ = −0.2 (2) × 10⁻⁸ K⁻²). The present thermal EOS enables us to accurately calculate the density of magnesite to the deep mantle conditions. Decarbonation of a subducting oceanic crust containing 2 wt.% magnesite would result in a 0.6% density reduction at 30 GPa and 1273 K. Using the new EOS parameters we performed thermodynamic calculations for magnesite decarbonation reactions at pressures to 20 GPa. We also estimated stability of magnesite-bearing assemblages in the lower mantle.  相似文献   

Comparison of Synchrotron Radiation X-Ray Fluorescence with Conventional Techniques for the Analysis of Sedimentary Samples   总被引：3，自引：0，他引：3  

Michael A. Phedorin  Vladislav A. Bobrov  Evgeny P. Chebykin  Evgeny L. Goldberg  Michael S. Melgunov  Svetlana V. Filippova  Konstantin V. Zolotarev 《Geostandards and Geoanalytical Research》2000,24(2):205-216

A comparison is made of elemental analyses of sediment samples (lake bottom sediments and sediments from the petroliferous Bazhenovka Formation) by five competitive methods (synchrotron radiation X-ray fluorescence (SR-XRF), INAA, ICP-MS, AAS and traditional XRF). The object of this study was to identify the most suitable analytical techniques for applications in sedimentary geochemistry. Advantages and shortcomings of the five techniques were considered with respect to applications related to studies of palaeo-climate changes recorded in sedimentary cores from Lake Baikal and the geochemical stratigraphy of the Bazhenovka Formation, which is rich in organic material. We have concluded that SR-XRF was the best technique for producing extensive analytical data series, from the point of view of its speed, ease of application, cost, non-destructive nature and sensitivity, which allowed for the simultaneous determination of more than twenty elements of geochemical interest in small samples of sediments. An additional benefit of the method was demonstrated when used for the independent certification of geological reference materials. International reference samples BIL-1 and SDO-1 were certified by means of this method without use of reference materials. Analyses were based on the physics of the theory of energy transport.  相似文献   

地球物理学及大地构造学中关于地壳均衡的新模型(英文)     

Tyap.  KF 《地学前缘》2000,7(1):69-78

讨论了一些有关地壳均衡概念的模型。业已证明 ,这些模型既不能用以正确评估地球的平衡状态 ,也不能用以解释构造成因。介绍一种新的地壳均衡模型 ,它与地球的某一种旋转方式相适应。地球体与球的偏差 ,被用来作为地球平衡的判据。地球被认为是在偏差趋近于零的那些点上得到平衡的。地球体与球体之间标志的差异 ,是由地球外壳中地质作用的方向所确定的。所提出的是大地地壳均衡模型 ,是地壳中构造形成新旋转假说的基础。  相似文献   

Distance Between Two Arbitrary Unperturbed Orbits     

Roman V. Baluyev  Konstantin V. Kholshevnikov 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):287-300

In the paper by Kholshevnikov and Vassilie, 1999, (see also references therein) the problem of finding critical points of the distance function between two confocal Keplerian elliptic orbits (hence finding the distance between them in the sense of set theory) is reduced to the determination of all real roots of a trigonometric polynomial of degree eight. In non-degenerate cases a polynomial of lower degree with such properties does not exist. Here we extend the results to all possible cases of ordered pairs of orbits in the Two–Body–Problem. There are nine main cases corresponding to three main types of orbits: ellipse, hyperbola, and parabola. Note that the ellipse–hyperbola and hyperbola–ellipse cases are not equivalent as we exclude the variable marking the position on the second curve. For our purposes rectilinear trajectories can be treated as particular (not limiting) cases of elliptic or hyperbolic orbits.  相似文献   

Restructuring the kiosk trade in St. Petersburg: A new retail trade model for the post-Soviet period     

Konstantin E. Axenov  Izolde Brade  Alex G. Papadopoulos 《GeoJournal》1997,42(4):419-432

This study explores the commercial kiosk phenomenon as a reflection of the socio-spatial reordering of St. Petersburg following the introduction of market forces. In this article we interpret empirical evidence on the restructuring of commercial opportunity in post-Soviet St. Petersburg as a result of the emergence of the kiosk phenomenon. Kiosk trade and processes that contribute to it have emerged as tools for mass socioeconomic and psychological adaptation, following the dismantling of the communist regime. In our opinion, the emergence and continuing mutation of St. Petersburg kiosks constitutes the backbone of a process of middle-class formation. An extensive field research of 1989, 1994 and 1995 made it possible to study the dynamics of spatial structures of kiosk phenomenon. It is our final conclusion that kiosks will remain an important feature of St. Petersburgs commercial geography in the foreseeable future.  相似文献