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The Solubility of Sulphur in Hydrous Rhyolitic Melts 总被引:1,自引:1,他引:1
Experiments performed at 2 kbar, in the temperature range 8001000°C,with fO2 between NNO2·3 and NNO+2·9 (whereNNO is the nickelnickel oxide buffer), and varying amountsof sulphur added to hydrous metaluminous rhyolite bulk compositions,were used to constrain the solubility of sulphur in rhyolitemelts. The results show that fS2 exerts a dominant control onthe sulphur solubility in hydrous silicate melts and that, dependingon fO2, a rhyolitic melt can reach sulphur contents close to1000 ppm at high fS2. At fO2 below NNO+1, the addition of ironto a sulphur-bearing rhyolite magma produces massive crystallizationof pyrrhotite and does not enhance the sulphur solubility ofthe melt. For a given fO2, the melt-sulphur-content increaseswith fS2. For fixed fO2 and fS2, temperature exerts a positivecontrol on sulphur solubilities, at least for fO2 below NNO+1.The mole fraction of dissolved sulphur exhibits essentiallylinear dependence on fH2S at low fO2 and, although the experimentalevidence is less clear, on fSO2 at high fO2. The minimum insulphur solubility corresponds to the redox range where bothfH2S and fSO2 are approximately equal. A thermodynamic modelof sulphur solubility in hydrous rhyolite melts is derived assumingthat total dissolved sulphur results from the additive effectsof H2S and SO2 dissolution reactions. The model reproduces wellthe minimum of sulphur solubility at around NNO+1, in additionto the variation of the sulphide to sulphate ratio with fO2.A simple empirical model of sulphur solubility in rhyoliticmelts is derived, and shows good correspondence between modeland observations for high-silica rhyolites. KEY WORDS: sulphur; solubility; rhyolite; thermodynamics; fO2; fS2 相似文献
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Lithospheric Mantle Evolution during Continental Break-Up: The West Iberia Non-Volcanic Passive Margin 总被引:6,自引:0,他引:6
CHAZOT GILLES; CHARPENTIER SOPHIE; KORNPROBST JACQUES; VANNUCCI RICCARDO; LUAIS BEATRICE 《Journal of Petrology》2005,46(12):2527-2568
Ultramafic (lherzolites, metasomatized peridotites, harzburgites,websterites and clinopyroxenites) and mafic igneous (basalts,dolerites, diorites and gabbros) rocks exposed at the sea-flooralong the West Iberia continental margin represent a rare opportunityto study the transition zone between continental and oceaniclithosphere. The igneous rocks are enriched in LREE, unlikeNorth Atlantic MORB. A correlation between their 143Nd/144Ndisotopic composition and Ce/Yb ratio suggests that they originatefrom mixing between partial melts of a depleted mantle sourcesimilar to DMM and of an enriched mantle source which may residewithin the continental lithosphere. Clinopyroxenes and amphibolesin the ultramafic rocks are LREE depleted and have flat HREEpatterns with concentrations higher than those of abyssal peridotites.Clinopyroxenes in the harzburgites are less LREE depleted buthave lower HREE concentrations. The clinopyroxenes in the GaliciaBank (GB) lherzolites have radiogenic Nd (143Nd/144Nd rangingfrom 0·512937 to 0·513402) and unradiogenic Sr(87Sr/86Sr ranging from 0·702100 to 0·702311)isotopic ratios similar to, or higher than, DMM (Depleted MORBMantle) whereas the clinopyroxenes in the Iberia Abyssal Plainwebsterites have low-Nd isotopic compositions (143Nd/144Nd rangingfrom 0·512283 to 0·512553) with high-Sr isotopicratios (87Sr/86Sr ranging from 0·704170 to 0·705919).Amphiboles in Galicia Bank lherzolites and diorites have NdSrisotopic compositions (143Nd/144Nd from 0·512804 to 0·512938and 87Sr/86Sr from 0·703243 to 0·703887) intermediatebetween those of the clinopyroxenes from the Galicia Bank andthe Iberia Abyssal Plain, but similar to the clinopyroxenesin the 5100 Hill harzburgite (143Nd/144Nd = 0·512865and 87Sr/86Sr = 0·703591) and to the igneous rocks (143Nd/144Ndranging from 0·512729 to 0·513121 and 87Sr/86Srranging from 0·702255 to 0·705109). The majorand trace element compositions of cpx in the Galicia Bank spinellherzolites provide evidence for large-scale refertilizationof the lithospheric upper mantle by MORB-like tholeiitic melts.The associated harzburgites did not undergo partial meltingduring the rifting stage, but, in earlier times, probably during,or even before, the Hercynian orogeny. Iberia Abyssal Plainwebsterites are interpreted as high-pressure cumulates formedin the mantle. Their high Sm/Nd ratios (from 0·43 to0·67) coupled with very low-Nd isotopic compositionsare best explained by a two-stage history: formation of thecumulates from the percolation of enriched melts long beforethe rifting, followed by low-degree partial melting of the pyroxenites,accounting for their LREE depletion. This last event probablyoccurs during the rifting episode, 122 Myr ago. The isotopicheterogeneities observed in the ultramafic rocks of the Iberiamargin were already present at the time of the rifting event.They reflect a long and complex history of depletion and enrichmentevents in an old part of the mantle, and provide strong argumentsfor a sub-continental origin of this part of the upper mantle. KEY WORDS: Iberia margin; mantle peridotites; igneous rocks; petrology; geochemistry 相似文献
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