Structure of Cu-bearing orthopyroxene, Mg(Cu.56,Mg.44)Si2O6, and behavior of Cu2+ in the orthopyroxene structure     

T. Tachi  H. Horiuchi  H. Nagasawa 《Physics and Chemistry of Minerals》1997,24(7):463-476

Cu-bearing pyroxene, Mg(Cu.₅₆,Mg.₄₄)Si₂O₆, has been synthesized by a flux method and crystal structure refinement has been performed by single crystal X-ray diffraction. It is found that the crystal structure is orthorhombic (space group Pbca) with unit cell dimensions of a=18.221(4), b=8.890(1), c=5.2260(7)Å and the cell volume of 846.5( )3ų. In the M2-site one of the M-O bonds(M-O3B) is extremely expanded from 2.444(2) in enstatite to 2.732(2), thus the coordination polyhedron around M2-site is regarded as square pyramidal rather than square planar or octahedral. It is also found that the M1-site in the pyroxene structure is occupied almost exclusively by Mg, while the M2-site is almost evenly occupied by Mg and Cu. The observed extreme site preference shown by Cu²⁺ is unusual among the divalent cations with similar ionic sizes.  相似文献   

Patterns in the hydrogen and trace element compositions of mantle olivines   总被引：1，自引：0，他引：1  

M. Kurosawa  H. Yurimoto  S. Sueno 《Physics and Chemistry of Minerals》1997,24(6):385-395

 The concentrations of hydrogen and the other trace elements in olivines from mantle xenoliths have been determined by secondary ion mass spectrometry (SIMS) for clarifying the incorporation mechanism and the behavior of the hydrogen. The hydrogen contents in olivines from mantle xenoliths range from 10 to 60 ppm wt. H₂O and the concentration range is consistent with the previous infrared (IR) spectroscopic data. IR spectra of the olivine crystals show no effects of the weathering or secondary alteration. The hydrogen is distributed homogeneously among olivine grains in each mantle xenolith. However, the hydrogen contents of the olivine crystals are less than those for the olivine phenocrysts crystallized from the host magma. Olivine inclusions in diamonds also show similar hydrogen contents to the xenolithic olivines. Thus the hydrogen content of xenolithic olivines does not attain equilibrium with water in the host magma during the transportation from the Earth's mantle to the surface, and is taken as a reflection of the hydrogen condition in the mantle. Correlations of hydrogen with trivalent cation contents in garnet peridotitic olivines indicate the incorporation of hydrogen into mantle olivines by a coupled substitution mechanism, with the hydrogen present in the form of hydroxyl in oxygen positions adjacent to the M site vacancies. The hydrogen content of xenolithic olivines increases with pressure but decreases with increasing temperature, suggesting importance of olivine as a water reservoir at low temperature regions such as in subducting slabs. Received August 15, 1995/Revised, accepted November 19, 1996  相似文献   

Are assemblages of black bream (Acanthopagrus butcheri) in different estuaries genetically distinct?     

J.A. Chaplin  G.A. Baudains  H.S. Gill  R. Mcculloch  I.C. Potter 《International Journal of Salt Lake Research》1997,6(4):303-321

Samples of the estuarine-spawning teleostAcanthopagrus butcheri were collected from nine estuaries and a coastal lake, located in the Pilbara and South-western drainage divisions of Western Australia and distributed along a coastline covering a distance of nearly 2,000 km. The patterns of allozyme variation in these samples were used to explore the extent to which there was variation in the genetic compositions of black bream assemblages in geographically-isolated estuarine systems, and whether or not any such variation could be related to the geographical location or type of estuary. Although only three of 36 scorable loci (Gpi-1, Ldh andMdh-2) exhibited variation that could be used for analysis, there was considerable variation in allele frequencies at these loci among the different samples (mean F_ST=0.166). Much of the detected variation was attributable to differences between the samples collected from the two drainage divisions, which are located in very different climatic regions. Furthermore, the genetic compositions of samples from neighbouring estuaries were typically more similar to each other than to those of samples collected from more distantly-located systems. However, the assemblages in one west coast and two south coast estuaries, that are closed to the ocean for extensive periods of time during the year, all showed very similar genetic compositions. Nevertheless, it is crucial to recognise that, pairwise comparisons of samples collected from the different estuaries, both within and between the two drainage divisions, almost invariably showed statistically significant differences in allele frequencies at one or more loci. Thus, our results indicate that the local populations of black bream in individual estuaries are genetically distinct, which is probably a consequence of both a limited movement by individuals between estuaries and the effects of differences in regional and local environmental conditions.  相似文献   

Historical novels and historical geography     

Alan R H Baker 《Area》1997,29(3):269-273

  相似文献   

Comment on: 'Can horizontal P waves be trapped and resonate in a shallow sedimentary basin?' by F. J. Sácnhez-Sesma and F. LuzÓ     

J. L. Mateos  O. Novaro  T. H. Seligman  J. Flores 《Geophysical Journal International》1997,129(1):212-214

We show that most of the arguments in the above paper are either incorrect or irrelevant to the point the authors are trying to make. We show that their results have no bearing on the model proposed by our group, as they claim. They discuss the seismic response of a valley with a 2-D trapezoidal cross-section in a vertical plane, whereas we dealt with a closed basin with a 2-D cross-section but of arbitrary geometry and in the horizontal plane. Even more significantly, the width of the valley they use is much smaller than the wavelength of the horizontal P waves that can resonate, thereby precluding any possibility of them being trapped. Therefore, their arguments do not clarify the issue posed in the title of their article.  相似文献   

Petrochemistry of Jurassic and Cretaceous tholeiites from Kong Karls Land, Svalbard, and their relation to Mesozoic magmatism in the Arctic     

JOHN C. BAILEY  MOGENS H. RASMUSSEN 《Polar research》1997,16(1):37-62

A study of the whole-rock geochemistry and mineral chemistry of high-TiO₂ Upper Jurassic and medium-TiO₂ Lower Cretaceous basalts from Kong Karls Land, Svalbard, is presented. Geochemical criteria indicate that the basalts are initial rifting tholeiites with weak signs of crustal contamination. The Upper Jurassic basalts appear to be associated with the Olga Rift, part of a trans-Barents rift system which failed to link the proto-Atlantic and proto-Arctic basins. The Lower Cretaceous basalts may be more closely related to initial rifting tholeiites on Franz Josef Land and Spitsbergen generated during the rifting stage of opening of the Canada Basin. During break-up of the Barents Shelf, the sequence of magma types corresponds to the pre-, syn- and post-rifting stages established in other areas of continental break-up. Evidence for a possible hot-spot or plume trail, extending from Siberia to the Yermak Plateau over 250 Ma, is assembled.  相似文献   

Monitoring of rapid salt weathering in the central Namib Desert using limestone blocks     

A.S. Goudie  H.A. Viles  A.G. Parker 《Journal of Arid Environments》1997,37(4):581-598

Pre-weighed blocks of a Jurassic Limestone were exposed on the ground surface in the coastal Namib Desert for a period of 2 years. The environment is both salty and foggy. Some of the blocks suffered extensive disintegration, and laboratory analyses (including geochemistry, XRD and SEM) indicate that the weathered samples have a high halite (sodium chloride) content. Cycles of wetting and drying associated with the frequent fog events of the area cause cycles of halite crystallization. Rocks exposed at the surface absorb salts from the surrounding desert surface and then disintegrate, contributing to planation of the landscape.  相似文献   

POLITICS AND MEDIA RICHNESS IN WORLD WIDE WEB REPRESENTATIONS OF THE FORMER YUGOSLAVIA     

MICHELE H. JACKSON  DARREN PURCELL 《Geographical review》1997,87(2):219-239

ABSTRACT. Media-richness theory is applied to World Wide Web sites to demonstrate how Web-page designers are using hypertext markup language to shape conceptions of place and to provide competing visions of the events that have transpired in the former Yugoslavia. We argue that Web sites vary in their interactivity, strategically, to reduce equivocality surrounding conceptions of space and territory. Media-richness theory as applied here allows the development of a heuristic to understand how Web pages communicate information about geographical entities and help to shape perceptions of place.  相似文献   

Seismic source study of the Racha-Dzhava (Georgia) earthquake from aftershocks and broad-band teleseismic body-wave records: an example of active nappe tectonics   总被引：1，自引：0，他引：1  

H. Fuenzalida  L. Rivera  H. Haessler  D. Legrand  H. Philip  L. Dorbath    D. McCormack  S. Arefiev  C. Langer  A. Cisternas 《Geophysical Journal International》1997,130(1):29-46

  相似文献   

Improved methods for solving for the magnetic field in E-polarization induction problems with fixed and staggered grids     

J. T. Weaver  X. H. Pu  A. K. Agarwal 《Geophysical Journal International》1996,126(2):437-446

  相似文献