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We have investigated the stability and composition of potassiumamphibole and its high-pressure breakdown product phase X insynthetic peralkaline and subalkaline KNCMASH (K2ONa2OCaOMgOAl2O3SiO2H2O)and natural KLB-1 peridotite bulk compositions between 10 and23 GPa at 8001800°C. In the KNCMASH system, potassiumamphibole reaches its upper pressure stability limit at 1315GPa at 相似文献
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KONZETT JURGEN; MILLER CHRISTINE; ARMSTRONG RICHARD; THONI MARTIN 《Journal of Petrology》2005,46(4):717-747
Olivine-rich rocks containing olivine + orthopyroxene + spinel+ Ca-amphibole ± clinopyroxene ± garnet are presentin the central ÖtztalStubai crystalline basementassociated with eclogites of tholeiitic affinity. These rockscontain centimetre-sized garnet layers and lenses with garnet+ clinopyroxene ± corundum. Protoliths of the olivine-richrocks are thought to be olivine + orthopyroxene + spinel dominatedcumulates generated from an already differentiated Fe-rich () tholeiitic magma that was emplaced into shallowcontinental crust. Protoliths of the garnet-rich rocks are interpretedas layers enriched in plagioclase and spinel intercalated ina cumulate rock sequence that is devoid of, or poor in, plagioclase.UPb sensitive high-resolution ion microprobe dating ofzircons from a garnet layer indicates that emplacement of thecumulates took place no later than 517 ± 7 Myr ago. Aftertheir emplacement, the cumulates were subjected to progressivemetamorphism, reaching eclogite-facies conditions around 800°Cand >2 GPa during a Variscan metamorphic event between 350and 360 Ma. Progressive high-P metamorphism induced breakdownof spinel to form garnet in the olivine-rich rocks and of plagioclase+ spinel to form garnet + clinopyroxene ± corundum inthe garnet layers. Retrogressive metamorphism at T 650680°Cled to the formation of Ca-amphibole, chlorite and talc in theolivine-rich rocks. In the garnet layers, högbomite formedfrom corundum + spinel along with Al-rich spinel, Ca-amphibole,chlorite, aspidolitepreiswerkite, magnetite, ilmeniteand apatite at the interface between olivine-rich rocks andgarnet layers at P < 0·8 GPa. Progressive desiccationof retrogade fluids through crystallization of hydrous phasesled to a local formation of saline brines in the garnet layers.The presence of these brines resulted in a late-stage formationof Fe- and K-rich Ca-amphibole and Sr-rich apatite, both characterizedby extremely high Cl contents of up to 3·5 and 6·5wt % Cl, respectively. KEY WORDS: cumulates; Variscan metamorphism; SHRIMP dating; högbomite; saline brines 相似文献
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JURGEN BOHNER 《Boreas: An International Journal of Quaternary Research》2006,35(2):279-295
Basic features of current spatial and seasonal climate variations in Central and High Asia are presented. Large-scale circulation modes were inferred from NCAR/CDAS General Circulation Model (GCM) data and interpreted with particular emphasis on the Asian Monsoon circulation. Using spatial high-resolution estimates of radiation, temperature and precipitation covering Central and High Asia in a regular grid network with a grid-cell spacing of 1 km2, topoclimatic variations are investigated and discussed with respect to their major barometric and topographic controls. In general, weather patterns of Central and High Asia are determined by tropical monsoon as well as extratropical circulation modes. Associated synoptic conditions and processes, in particular the alternation of tropical and polar air masses, lead to distinct large-scale variations valid for all climatic parameters in all seasons. The regional analysis and discussion of climatic gradients and environmental lapse rates stress the significant role of Asia's marked orography and its influence on advective processes, flow currents and topoclimatic settings. Preliminary estimations of the annual water balance, however, are still afflicted with major uncertainties owing to methodical limits in the spatial estimation of precipitation rates and widely lacking evapotranspiration records, particularly in the Tibetan Plateau and adjacent high mountain systems. Given the importance of the mountainous water resources for the affected economies, further regional investigations on the water cycle and its components are vital future tasks for climate research. 相似文献
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JERRY C. RITCHIE THOMAS J. JACKSON JURGEN D. GARBRECHT EARL H. GRISSINGER JOSEPH B. MURPHEY JAMES H. EVERITT 《水文科学杂志》2013,58(5):403-416
Abstract Vertical surface properties of the landscape were measured using a laser altimeter mounted in a small twin-engine aeroplane. The laser altimeter makes 4000 measurements per second with a vertical recording precision of 0.05 m for a single measurement. These airborne laser measurements were analysed to provide information on topography, vegetation canopy and stream and gully cross-sections. Laser altimeter data were used to measure small (less than 0.20 m deep) and large gullies and stream cross-sections. Vegetation canopy heights, cover, structure and distribution were determined in studies in Texas and Arizona. Laser measurements of vegetation cover and height were significantly correlated with ground measurements made with line-intercept methods. While conventional ground-based techniques may be used to make all these measurements, airborne laser altimeter techniques allow the data to be collected in a quick and efficient way over large and inaccessible areas. The airborne laser altimeter data can also help quantify various land surface parameters needed for natural resource and landscape management or required by hydrological simulation models. Measurements of landscape properties over large areas provide a better understanding of landscape functions and can lead to the development of better management plans to conserve and improve the productivity of natural resources. 相似文献
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An Experimental Investigation of the Influence of Water and Oxygen Fugacity on Differentiation of MORB at 200 MPa 总被引:10,自引:2,他引:10
Crystallization experiments were performed at 200 MPa in thetemperature range 1150950°C at oxygen fugacitiescorresponding to the quartzfayalitemagnetite (QFM)and MnOMn3O4 buffers to assess the role of water andfO2 on phase relations and differentiation trends in mid-oceanridge basalt (MORB) systems. Starting from a primitive (MgO9·8 wt %) and an evolved MORB (MgO 6·49 wt %),crystallization paths with four different water contents (0·354·7wt % H2O) have been investigated. In primitive MORB, olivineis the liquidus phase followed by plagioclase + clinopyroxene.Amphibole is present only at water-saturated conditions below1000°C, but not all fluid-saturated runs contain amphibole.Magnetite and orthopyroxene are not stable at low fO2 (QFM buffer).Residual liquids obtained at low fO2 show a tholeiitic differentiationtrend. The crystallization of magnetite at high fO2 (MnOMn3O4buffer) results in a decrease of melt FeO*/MgO ratio, causinga calc-alkaline differentiation trend. Because the magnetitecrystallization temperature is nearly independent of the H2Ocontent, in contrast to silicate minerals, the calc-alkalinedifferentiation trend is more pronounced at high water contents.Residual melts at 950°C in a primitive MORB system havecompositions approaching those of oceanic plagiogranites interms of SiO2 and K2O, but have Ca/Na ratios and FeO* contentsthat are too high compared with the natural rocks, implyingthat fractionation processes are necessary to reach typicalcompositions of natural oceanic plagiogranites. KEY WORDS: differentiation; MORB; oxygen fugacity; water activity; oceanic plagiogranite 相似文献
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High-pressurehigh-temperature experiments were performedin the range 715 GPa and 13001600°C to investigatethe stability and phase relations of the K- and Ba-dominantmembers of the crichtonite and magnetoplumbite series of phasesin simplified bulk compositions in the systems TiO2ZrO2Cr2O3Fe2O3BaOK2Oand TiO2Cr2O3Fe2O3BaOK2O. Both seriesof phases occur as inclusions in diamond and/or as constituentsof metasomatized peridotite mantle xenoliths sampled by kimberlitesor alkaline lamprophyres. They can accommodate large ion lithophileelements (LILE) and high field strength elements (HFSE) on awt % level and, hence, can critically influence the LILE andHFSE budget of a metasomatized peridotite even if present onlyin trace amounts. The Ba and K end-members of the crichtoniteseries, lindsleyite and mathiasite, are stable to 11 GPa and15001600°C. Between 11 and 12 GPa, lindsleyite breaksdown to form two BaCr-titanates of unknown structurethat persist to at least 13 GPa. The high-pressure breakdownproduct of mathiasite is a KCr-titanate with an idealizedformula KM7O12, where M = Ti, Cr, Mg, Fe. This phase possessesspace group P63/m with a = 9·175(2) Å, c = 2·879(1)Å, V = 209·9(1) Å3. Towards high temperatures,lindsleyite persists to 1600°C, whereas mathiasite breaksdown between 1500 and 1600°C to form a number of complexTiCr-oxides. Ba and K end-members of the magnetoplumbiteseries, hawthorneite and yimengite, are stable in runs at 7,10 and 15 GPa between 1300 and 1400°C coexisting with anumber of TiCr-oxides. Molar mixtures (1:1) of lindsleyitemathiasiteand hawthorneiteyimengite were studied at 710GPa and 13001400°C, and 915 GPa and 11501400°C,respectively. In the system lindsleyitemathiasite, onehomogeneous BaK phase is stable, which shows a systematicincrease in the K/(K + Ba) ratio with increasing pressure. Inthe system hawthorneiteyimengite, two coexisting BaKphases appear, which are Ba rich and Ba poor, respectively.The data obtained from this study suggest that Ba- and K-dominantmembers of the crichtonite and magnetoplumbite series of phasesare potentially stable not only throughout the entire subcontinentallithosphere but also under conditions of an average present-daymantle adiabat in the underlying asthenosphere to a depth ofup to 450 km. At still higher pressures, both K and Ba may remainstored in alkali titanates that would also be eminently suitablefor the transport of other ions with large ionic radii. KEY WORDS: crichtonite; magnetoplumbite; high-PT experiments; phase relations; upper mantle 相似文献
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