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51.
Travel distances in gravel-bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge. Mean distance of movement, irrespective of grain size, is weakly correlated with stream power, especially near the threshold of movement. There may be several reasons for the weak correlation, including variable effects of bed structure, varying magnitudes of sediment mobilizing events and sampling problems. Grain size itself is of marginal significance. The virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period. Better results are obtained by relating the virtual rate of travel to the first peak of the flow event only. This implies that the initial seeding of the tagged particles dominates the observations. Nonetheless, an underlying general relation is indicated by the data, which are derived from a wide range of flow regime types. 相似文献
52.
Dr. Ni Wen Dr. A. J. Boyce Dr. A. E. Fallick Dr. J. R. Ashworth Dr. R. A. Ixer 《Mineralogy and Petrology》1996,57(1-2):73-89
Summary Polymetallicmajor veins of the West Carbery district (County Cork) are compared with the nearby stratiform-disseminated copper mineralization in metasedimentary rocks, containingminor veins (metamorphic quartz veins and veinlets). These stratiform deposits are hosted by non-marine Devonian sediments (Old Red Sandstone), metamorphosed in the Hercynian orogeny. In sulphides from the stratiform deposits and minor veins, isotopic compositions of sulphur (34S) range from – 21.00 to + 5.14%0, consistent with the vein sulphide being remobilized stratiform-disseminated sulphide, and the latter being of diagenetic bacteriogenic origin. Sulphate (barite), found in veins separate from the sulphides, has 34S + 12.3 to + 15.7%0. consistent with groundwater origin. In minor-vein quartz, fluid inclusions have homogenization temperatures consistent with trapping under the estimated peak-metamorphic conditions (300–400°C, 1–3 kbar).In the major veins, sulphide 34S (–15.8 to –4.2 0) suggest remobilization of diagenetic sulphide. Oxygen and hydrogen isotopes suggest deposition from metamorphic fluids (calculated 18OH2O approximately + 8 to + l3%0, measured range of D –52.2 to –27.3%0). Immiscible C02-bearing fluids were trapped in the temperature range 280–350°C with fluid pressure < ca. 600 bar. The inferred pressure-temperature history is attributed to late-metamorphic uplift, with fluid pressures falling below lithostatic. The sulphide-bearing veins are interpreted as a small-scale example of redistribution of mineral deposits by metamorphic fluids.
With 6 Figures 相似文献
Die Genese Cu führender Quarzgdnge durch metamorphe Remobilisation aus stratiformen Rotsedimenten, SW County Cork, Irland
Zusammenfassung Polymetallische Erzgänge (major veins) des westlichen Carbery Distriktes (County Cork) werden mit kleineren Gängchen (minor veins), die in den benachbarten, eine disseminierte stratiforme Cu-Vererzung führenden, Metasedimenten liegen, verglichen. Diese stratiformen Lagerstätten sind an nichtmarine devonische Sedimente (Old Red Sandstone), die während der hercynischen Orogenese metamorphisiert wurden, gebunden. Die Zusammensetzung der Schwefelisotope (34S) der Sulfide in der disseminierten Vererzung und in den kleineren Gängen variiert von –21.00 bis –5.14%0. Diese Zusammensetzung ist mit der Interpretation, daß der Schwefel in den Gängchen aus den stratiformen disseminierten Sulfiden remobilisiert wurde, die ihrerseits diagenetischbakteriogene Signatur zeigen, konsistent: Die 345-Werte der Sulfate (Baryt) in den Gängchen variieren von + 12.3 bis + 15.7%0, was mit einer Herkunft aus Grundwässern übereinstimmt. Die Homogenisierungs-Temperaturen der FlüsBigkeitseinschlüsse in Quarz der Gängchen sind mit einem Einschluß der Fluide während des Höhepunktes der Metamorphose (300–400°C, l-3 kbar) konsistent.In den polymetallischen Erzgängen weisen die 34S-Werte (–15.8 bis –4.2%0) auf die Remobilisation diagenetischen Schwefels, die Sauerstoff und Wasserstoffisotope auf Ausfällung aus metamorphen Wässern hin. Die berechneten 18O-Werte liegen zwischen ca. +8 bis +13%0 die gemessenen H-Werte zwischen –52.2 bis –27.3%0. Nicht mischbare C02-führende Fluide wurden im Temperaturbereich von 280–350°C bei Fluid-Drucken < ca. 600 bar eingeschlossen. Der abgeleitete P-T Pfad wird mit spätmetamorpher Hebung, während der der Fluiddruck unter den lithostatischen Druck fiel, erklärt. Die Sulfid-führenden Gänge werden als kleinmaßstäbliche Beispiele für Wiederverteilung von Minerallagerstätten durch metamorphe Fluide gedeutet.
With 6 Figures 相似文献
53.
54.
María Luisa Crawford 《Contributions to Mineralogy and Petrology》1966,13(3):269-294
Two suites of regionally metamorphosed semi-pelitic schists were studied in order to investigate the paragenesis of low temperature plagioclase, from which something may be inferred as to the nature of the peristerite solvus at the temperatures and pressures of formation of these rocks: one from the Gile Mountain Formation in the Hanover and Mt. Cube quadrangles, eastern Vermont, U.S.A.; the other from the Alpine schists along the Haast River, South Westland, New Zealand. Plagioclase, muscovite, biotite, chlorite, carbonate, and garnet compositions were determined with an ARL EMX electron probe microanalyzer. The variation in plagioclase composition with increasing grade in the Vermont schists suggests that the peristerite solvus is asymmetrical with a near vertical albite-rich side and a sloping oligoclase-rich side. The top of the solvus appears to lie slightly above the temperature expressed by the almandine isograd in these schists. The compositions of the coexisting albite and oligoclase in the New Zealand rocks suggest a lower geothermal gradient than in Vermont, creating a different pattern of variation in plagioclase composition. Distribution diagrams of Mg, Ti, and AlIV for muscovite-biotite and chlorite-biotite pairs in both suites of rocks support the hypothesis that the plagioclase relations observed represent equilibrium. 相似文献
55.
J. R. Ashworth J. J. Birdi T. F. Emmett 《Contributions to Mineralogy and Petrology》1992,109(3):307-325
Retrograde coronas of Caledonian age, between clinopyroxene and plagioclase in the Jotun Nappe Complex, Norway, illustrate the effects of diffusion kinetics on mineral distributions among layers and on the compositions of hornblende-actinolite. One corona type comprises a symplectite of epidote + quartz adjacent to plagioclase, and a less well-organized intergrowth of amphibole + quartz replacing clinopyroxene. The observed mineral proportions imply an open-system reaction, but the similarity of Al/Si ratios in reactant plagioclase and product symplectite indicates approximate conservation of Al2O3 and SiO2. The largest inferred open-system flux is a loss of CaO, mostly derived from consumption of clinopyroxene. The approximate layer structure, Pl|Ep + Qtz|Hbl + Qtz|Act±Hbl + Qtz|Cpx, is modelled using the theory of steady-state diffusion-controlled growth with local equilibrium. To obtain a solution, it is necessary to use a reactant plagioclase composition which takes into account aluminous (epidote) inclusions. The results indicate that, in terms of Onsager diffusion coefficients L
ii
, Ca is more mobile than AL (L
CaCa/L
AlAl3.) (where means greater than or approximately equal to). This behaviour of Ca is comparable with that of Mg in previously studied coronas around olivine. Si is non-diffusing in the present modelling, because of silica saturation. Oxidation of some Fe2+ to Fe3+ occurs within the corona. Mg diffuses towards its source (clinopyroxene) to maintain local equilibrium. Other coronas consist of two layers, hornblende adjacent to plagioclase and zoned amphibole + quartz adjacent to clinopyroxene. In the zoned layer, actinolitic hornblende forms relict patches, separated from quartz blebs by more aluminous hornblende. A preliminary steady-state, local-equilibrium model of grain-boundary diffusion explains the formation of low-Al and high-Al layers as due to Al immobility. Zoning and replacement are qualitatively explained in terms of evolution of actinolite to more stable aluminous compositions. This is modelled by a non-steady-state modification of the theory, retaining local equilibrium in grain boundaries while relatively steep zoning profiles develop in grain interiors through slow intracrystalline diffusion. Replacement of actinolite by hornblende does not require a change in P–T conditions if actinolite is a kinetically determined, non-equilibrium product. The common preservation of a sharp contact between hornblende and actionolite layers may be explained by ineffectiveness of intracrystalline diffusion: according to the theory, given sufficient grain-boundary Al flux, a metastable actinolite + quartz layer in contact with hornblende may be diffusionally stable and may continue to grow in a steady state. 相似文献
56.
Rivalenti Giorgio Mazzucchelli Maurizio Vannucci Riccardo Hofmann Albrecht W. Ottolini Luisa Bottazzi Piero Obermiller Walter 《Contributions to Mineralogy and Petrology》1995,122(3):275-288
Field, mineralogical and petrological data are presented on a newly found carbonatite occurrence associated with “kamafugite”
lava at Cupaello, central Italy. This carbonatite occurrence is part of the Late Pleistocene Umbria-Latium ultra-alkaline
district (ULUD) which extends southwards within the Apennines to Mount Vulture, delineating an important magmatic province
along the most peripheral belt of the Tyrrhenian extensional tectonic system. This province is distinct, but probably related
genetically with the more abundant and common leucite-bearing assemblages of the Roman Comagmatic Region and represents the
first reported occurrence of carbonatite assemblages in the Mediterranean Basin. The Cupaello suite indicates that primary
or near-primary mantle silicate melts of “kamafugitic” composition are transitional with Ca-carbonatite liquid and provides
direct evidence of immiscibility of carbonatite from “kamafugite” magma. It is inferred that a primary mantle origin of Ca-carbonatites
is conditional upon a potential silicate magma that may be coupled with the carbonatite, but may not have reached the surface.
The data indicate a strong genetic link between ULUD Ca-carbonatites and some African analogues, supporting the view that
their genesis depends on similar source and associated tectonic conditions.
Received: 17 January 1995 / Accepted: 14 June 1995 相似文献
57.
Allan C. Ashworth Donald P. Schwert William A. Watts H.E. Wright 《Quaternary Research》1981,16(1):66-79
The Norwood site in Sibley Co., Minnesota, contains 1.6 m of silt resting on till and overlain by peat. The base of the peat has been radiocarbon dated at 12,400 ± 60 and the top at 11,200 ± 250 yr B.P. The pollen, plant macrofossils, and insect remains in the basal silt consist of boreal species inhabiting open environments, but not tundra. No modern analogue exists for the insect assemblage, which includes elements of boreal forest, tundra-forest, and western affinities. The transition from an unstable open environment to a stable coniferous forest is reflected by both plant and insect fossils and is interpreted as a successional rather than a climatic event. During this time of significant biologic change, the climate is inferred to have been relatively uniform, with temperatures similar to those presently existing in the boreal forest south of the tundra-forest transition zone. The geologic and ecologic succession at Norwood is generally similar to that presently associated with ice stagnation of the Klutlan Glacier in the Yukon Territory. Localized successional sequences similar to those at Norwood are conceived to have occurred repeatedly during the melting of the Laurentide ice, and thus the proposed model has potentially broad application to the interpretation of late-glacial sequences. 相似文献
58.
Cordierite and garnet are common in migmatites adjoining Caldeonian (sensu lato) synorogenic intrusions in the Highlands of Scotland. Migmatitic hornfelses of the Huntly-Portsoy area, of particular interest in being closely associated with the regional andalusite/kyanite boundary, contain both of the pressure-sensitive sub-assemblages (cordierite-garnet-sillimanite) and (cordierite-garnet-ortho-pyroxene). In other areas regional metamorphism was of higher-pressure (kyanite-sillimanite) type, the metamorphic patterns having been subsequently modified at lower pressures. The subassemblage cordierite-garnet-sillimanite is found in pelites occurring near contacts of the Strontian Granodiorite and the nearby, but probably earlier, Glen Scaddle basic complex, where andalusite also occurs in the contact zone. The sub-assemblage cordierite-garnet-orthopyroxene is studied in migmatitic hornfelses of the Lochnagar aureole. Zoning of cordierite and garnet is found in all specimens, and results largely from retrograde diffusive reactions.The calibrations of the garnet-cordierite-sillimanite geobarometer by Thompson (1976) and by Holdaway and Lee (1977) are used to estimate pressures of migmatization. These calibrations give results 2–3 kbar lower than that of Hensen and Green (1973). In the Huntly-Portsoy area, where the pressure must have been close to that of the Al2SiO5 triple point, the Thompson result is 5.5 ±0.1 kbar. The calibration by Holdaway and Lee (1977), in which the H2O content of cordierite is treated, gives a maximum pressure estimate (for P
H
2
O=P) of 6.1 ±0.2 kbar. Rough calculations in which
is also estimated, using a simplified biotite-sillimanite-quartz dehydration reaction, give P=4.9±0.1 kbar with
0.6P.The Glen Scaddle area gives P = 5.6–5.9 kbar,
P by this method, compared with P=5.2–5.3 kbar by the Thompson calibration. The Strontian area gives lower values (<5kbar) despite being structurally below the Glen Scaddle area; this would indicate late origin of the cordierite-bearing migmatites and is consistent with their interpretation in terms of the thermal effects of the Strontian Granodiorite. The Lochnagar aureole is also relatively low-pressure.Estimates of maximum temperatures are 700–740 °C for the Strontian and Huntly-Portsoy areas, and 780–820 °C for the higher grade localities in the Glen Scaddle and Lochnagar areas, where orthopyroxene coexists with potash felspar and cordierite (but not sillimanite). It is likely that cordierite in all the rocks studied was produced as a result of melting reactions that are also responsible for migmatization. 相似文献
59.
Jim Best John Woodward Phil Ashworth Greg Sambrook Smith Chris Simpson 《Sedimentary Geology》2006,190(1-4):241-255
Discrete hollows in the bar tops of the South Saskatchewan River are described that form a newly-recognized morphological element of sandy braided rivers. These bar-top hollows, which are up to 1.7 m deep and may extend for 10–30 m down and across flow, have a circular to ovoid planform and are shown, through use of ground penetrating radar, to be filled by a series of distinct, often angle-of-repose, foresets. The hollows form by both erosion and bar-top deposition and may be generated by bar-tail accretion, cross-bar channel cutoff and subsequent fill or lateral accretion at the bar-head. Bar-top hollows occur in the upper part of the bar depositional sequence and may thus prove useful indicators for braid bar reconstruction in ancient sediments, and should not be confused with channel scour. 相似文献
60.
The effect of halogens on Zr diffusion and zircon dissolution in hydrous metaluminous granitic melts 总被引:1,自引:0,他引:1
Don R. Baker Aida Conte Carmela Freda Luisa Ottolini 《Contributions to Mineralogy and Petrology》2002,142(6):666-678
Diffusion of Zr and zircon solubility in hydrous, containing approximately 4.5 wt% H2O, metaluminous granitic melts with halogens, either 0.35 wt% Cl (LCl) or 1.2 wt% F (MRF), and in a halogen-free melt (LCO) were measured at 1.0 GPa and temperatures between 1,050 and 1,400 °C in a piston-cylinder apparatus using the zircon dissolution technique. Arrhenius equations for Zr diffusion in each hydrous melt composition are, for LCO with 4.4ǂ.4 wt% H2O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaI4aaocqaI4aaocqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaIZaWmcqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabiIda4aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIXaqmcqaI0aancqaIWaamcqGGUaGlcqaIXa % qmcqGHXcqScqaIZaWmcqaIZaWmcqGGUaGlcqaI5aqoaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!571F! D = 2.88 ±0.03x10 - 8 exp( [( - 140.1 ±33.9)/(RT)] )D = 2.88 \pm 0.03x10^{ - 8} \exp \left( {{{ - 140.1 \pm 33.9} \over {RT}}} \right) , for LCl with 4.5ǂ.5 wt% H2O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaIZaWmcqaIZaWmcqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaI1aqncqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabisda0aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIYaGmcqaI1aqncqaI0aancqGGUaGlcqaI4a % aocqGHXcqScqaI2aGncqaI0aancqGGUaGlcqaIXaqmaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!5719! D = 2.33 ±0.05x10 - 4 exp( [( - 254.8 ±64.1)/(RT)] )D = 2.33 \pm 0.05x10^{ - 4} \exp \left( {{{ - 254.8 \pm 64.1} \over {RT}}} \right) and for MRF with 4.9ǂ.3 wt% H2O: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacqWGebarcqGH9aqpcq % aIYaGmcqGGUaGlcqaI1aqncqaI0aancqGHXcqScqaIWaamcqGGUaGl % cqaIWaamcqaIZaWmcqWG4baEcqaIXaqmcqaIWaamdaahaaWcbeqaai % abgkHiTiabiwda1aaakiGbcwgaLjabcIha4jabcchaWnaabmaabaWa % aSaaaeaacqGHsislcqaIYaGmcqaIYaGmcqaIZaWmcqGGUaGlcqaI4a % aocqGHXcqScqaIXaqmcqaI1aqncqGGUaGlcqaI1aqnaeaacqWGsbGu % cqWGubavaaaacaGLOaGaayzkaaaaaa!5715! D = 2.54 ±0.03x10 - 5 exp( [( - 223.8 ±15.5)/(RT)] )D = 2.54 \pm 0.03x10^{ - 5} \exp \left( {{{ - 223.8 \pm 15.5} \over {RT}}} \right) . Solubilities determined by the dissolution technique were reversed for LCO +4.5ǂ.5 wt% H2O by crystallization of a Zr-enriched glass of LCO composition at 1,200 and 1,050 °C at 1.0 GPa. The solubility data were used to calculate partition coefficients of Zr between zircon and hydrous melt, which are given by the following expressions: for LCO % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGOnayJa % eG4mamZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 1aqncqGGUaGlcqaI4aaocqaI3aWnaaa!5924! lnDZrzircon/melt = 1.63( [10000/(T)] ) - 5.87\ln D_{Zr}^{zircon/melt} = 1.63\left( {{{10000} \over T}} \right) - 5.87 , for LCl % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGinaqJa % eG4naCZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 0aancqGGUaGlcqaI3aWncqaI1aqnaaa!5920! lnDZrzircon/melt = 1.47( [10000/(T)] ) - 4.75\ln D_{Zr}^{zircon/melt} = 1.47\left( {{{10000} \over T}} \right) - 4.75 and, for MRF by % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavP1wzZbItLDhis9wBH5garm % Wu51MyVXgaruWqVvNCPvMCG4uz3bqee0evGueE0jxyaibaieYlf9ir % Veeu0dXdh9vqqj-hEeeu0xXdbba9ev6pc9fs0-rqaqpepmKs4qpepe % I8kaL8kuc9pgc9q8qqaq-dhH6hb9hs0dXdHu6deP0u0-vr0-vr0db8 % meaabaqaciGacaGaaeaabaWaaeaaeaaakeaacyGGSbaBcqGGUbGBcq % WGebardaqhaaWcbaGaemOwaOLaemOCaihabaGaemOEaONaemyAaKMa % emOCaiNaem4yamMaem4Ba8MaemOBa4Maei4la8IaemyBa0Maemyzau % MaemiBaWMaemiDaqhaaOGaeyypa0JaeGymaeJaeiOla4IaeGinaqJa % eG4naCZaaeWaaeaadaWcaaqaaiabigdaXiabicdaWiabicdaWiabic % daWiabicdaWaqaaiabdsfaubaaaiaawIcacaGLPaaacqGHsislcqaI % 0aancqGGUaGlcqaI5aqocqaIXaqmaaa!591C! lnDZrzircon/melt = 1.47( [10000/(T)] ) - 4.91\ln D_{Zr}^{zircon/melt} = 1.47\left( {{{10000} \over T}} \right) - 4.91 . Experiments on the same compositions, but with water contents down to 0.5 wt%, demonstrated reductions in both the diffusion coefficient of Zr and zircon solubility in the melt. The addition of halogens at the concentration levels studied to metaluminous melts has a small effect on either the diffusion of Zr in the melt, or the solubility of zircon at all water concentrations and temperatures investigated. At 800 °C, the calculated diffusion coefficient of Zr is lowest in LCl, 9᎒-17 m2 s-1, and is highest in LCO, 4᎒-15 m2 s-1. Extrapolation of the halogen-free solubility data to a magmatic temperature of 800 °C yields solubilities of approximately one-third of those directly measured in similar compositions, predicted by earlier studies of zircon dissolution and based upon analyses of natural rocks. This discrepancy is attributed to the higher oxygen fugacity of the experiments of this study compared with previous studies and nature, and the effect of oxygen fugacity on the structural role of iron in the melt, which, in turn, affects zircon solubility, but does not significantly affect Zr diffusion. 相似文献