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Distribution of Ferric Iron in some Upper-Mantle Assemblages 总被引：16，自引：5，他引：11
The distribution of ferric iron among the phases of upper-mantlerocks, as a function of pressure (P), temperature (T) and bulkcomposition, has been studied using 57Fe Mssbauer spectroscopyto determine the Fe3+/Fe ratios of mineral separates from 35peridotite and pyroxenite samples. The whole-rock Fe3+ complementof a peridotite is typically shared approximately evenly amongthe major anhydrous phases (spinel and/or garnet, orthopyroxeneand clinopyroxene), with the important exception of olivine,which contains negligible Fe3+. Whole-rock Fe3+ contents areindependent of the T and P of equilibration of the rock, butshow a well-defined simple inverse correlation with the degreeof depletion in a basaltic component. Fe3+ in spinel and inboth pyroxenes from the spinel Iherzolite facies shows a positivecorrelation with temperature, presumably owing to the decreasein the modal abundance of spinel. In garnet peridotites, theFe3+ in garnet increases markedly with increasing T and P, whereasthat in clinopyroxene remains approximately constant. The complexnature of the partitioning of Fe3+ between mantle phases resultsin complicated patterns of the activities of the Fe3+ -bearingcomponents, and thus in calculated equilibrium fO2, which showlittle correlation with whole-rock Fe3+ or degree of depletion.Whether Fe3+ is taken into account or ignored in calculatingmineral formulae for geothermobarometry can have major effectson the resulting calculated T and P. For Fe-Mg exchange geothermometers,large errors must occur when applied to samples more oxidizedor reduced than the experimental calibrations, whose fO2 conditionsare largely unknown. Two-pyroxene thermometry is more immuneto this problem, and probably provides the most reliable P—Testimates. Accordingly, the convergence of P—T valuesderived for a given garnet peridotite assemblage may not necessarilybe indicative of mineral equilibrium. The prospects for thecalculation of accurate Fe3+ contents from electron microprobeanalyses by assuming stoichiometry are good for spinel, uncertainfor garnet, and distinctly poor for pyroxenes. KEY WORDS: mantle; oxidation; partitioning; peridotite; thermobarometry
*Corresponding author. Present address: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 1700, Victoria, B.C., V8W 2Y2, Canada 相似文献
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IMPLICATIONS FROM CHEMICAL,STRUCTURAL AND MINERALOGICAL STUDIES OF MAGNETIC MICROSPHERULES FROM AROUND THE LOWER YOUNGER DRYAS BOUNDARY (NEW MEXICO,USA) 
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下载免费PDF全文 ALEXANDRE V. ANDRONIKOV IRINA E. ANDRONIKOVA CLAYTON W. LOEHN BARBARA LAFUENTE JESSE A. M. BALLENGER GEORGE T. CRAWFORD DANTE S. LAURETTA 《Geografiska Annaler: Series A, Physical Geography》2016,98(1):39-59
Hollow magnetic microspherules from along the lower Younger Dryas boundary (c. 12.9 ka bp ) in New Mexico (USA) were studied using scanning electron microscopy, electron probe microanalysis, X‐ray diffraction, and laser‐ablation inductively coupled‐plasma mass spectrometry methods. The shell of the microspherules (10–15% of the spherule's diameter) displays dendritic surface textures, which are likely due to quenching during rapid cooling of molten material. Structurally, multiple single‐magnetite crystals attached together form the bulk of the microspherules. Iron dominates the microspherules’ composition (～90% FeOtot), Mn is the second most abundant element (up to 0.4% MnO), Al is detected in low concentrations (<0.30% of Al2O3). Among the trace elements, the rare earth elements display slightly fractionated patterns with concentrations of 0.1–1.0× CI chondrite. The microspherules contain elevated concentrations of Ni relative to detrital magnetite (up to 435 ppm) and very low concentrations of Ti (down to 5 ppm). Chemical, structural and mineralogical features of the microspherules do not contradict the existing models of the formation during ablation while a meteoroid goes through the Earth's atmosphere. Elevated concentrations of the magnetic microspherules in sediments can be a stratigraphic marker for the lower Younger Dryas boundary in North America. 相似文献
3.
Similar V/Sc Systematics in MORB and Arc Basalts: Implications for the Oxygen Fugacities of their Mantle Source Regions 总被引：8，自引：0，他引：8
AEOLUS LEE CIN-TY; LEEMAN WILLIAM P.; CANIL DANTE; LI ZHENG-XUE A 《Journal of Petrology》2005,46(11):2313-2336
V/Sc systematics in peridotites, mid-ocean ridge basalts andarc basalts are investigated to constrain the variation of fO2in the asthenospheric mantle. V/Sc ratios are used here to ‘seethrough’ those processes that can modify barometric fO2determinations in mantle rocks and/or magmas: early fractionalcrystallization, degassing, crustal assimilation and mantlemetasomatism. Melting models are combined here with a literaturedatabase on peridotites, arc lavas and mid-ocean ridge basalts,along with new, more precise data on peridotites and selectedarc lavas. V/Sc ratios in primitive arc lavas from the Cascadesmagmatic arc are correlated with fluid-mobile elements (e.g.Ba and K), indicating that fluids may subtly influence fO2 duringmelting. However, for the most part, the average V/Sc-inferredfO2s of arc basalts, MORB and peridotites are remarkably similar(–1·25 to +0·5 log units from the FMQ buffer)and disagree with the observation that the barometric fO2s ofarc lavas are several orders of magnitude higher. These observationssuggest that the upper part of the Earth's mantle may be stronglybuffered in terms of fO2. The higher barometric fO2s of arclavas and some arc-related xenoliths may be due respectivelyto magmatic differentiation processes and to exposure to large,time-integrated fluid fluxes incurred during the long-term stabilityof the lithospheric mantle. KEY WORDS: vanadium; scandium; oxygen fugacity; mantle; arcs 相似文献
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Origin of Phlogopite in Mantle Xenoliths from Kostal Lake, Wells Gray Park, British Columbia 总被引：1，自引：2，他引：1
Phlogopite has been recognized for the first time in ultramaficxenoliths from the Canadian Cordillera. The phlogopite-bearingxenoliths are hosted in post-glacial basanitoid flows and ejectaof the Kostal Lake volcanic center, British Columbia. The xenolithassemblage consists of 60% cumulate-textured wehrlites, and40% coarse-textured lherzolites, harzburgites, dunites, andolivine websterites. The phlogopite occurs: (1) as sub-euhedral grains along grainboundaries in dunite and lherzolite xenoliths; or (2) alongorthopyroxene lamellae exsolved from intercumulus clinopyroxenein the wehrlite xenoliths; or (3) as grains hosted in 10–100pm diameter fluid inclusions in clinopyroxene of all xenoliths.The phlogopites do not show any reaction relationships withother phases in any of the xenoliths studied. Phlogopites ina given xenolith have Mg/Mg + Fe2+ similar to that of coexistingolivine, clinopyroxene, and orthopyroxene. The partitioningof Fe and Mg between phlogopite and coexisting olivine and clinopyroxeneis similar to that observed in other phlogopite-bearing mantlexenoliths, and in high-pressure melting experiments on rockswith similar bulk compositions. This indicates that the phlogopitesin xenoliths from Kostal Lake have equilibrated with these coexistingphases. The occurrence of phlogopites in fluid inclusions containingNa, K, Cl, P, and S, suggests that incompatible element-enrichedhydrous fluids/melts fluxed this part of the upper mantle beneatheastern British Columbia. Metasomatism of the upper mantle beneathKostal Lake probably occurred prior to Quaternary alkaline magmatism(7550–400 B.P.) and after the initial volcanism whichformed the wehrlite cumulates (3–5 Ma). Metasomatism causedoverall oxidation of the upper mantle beneath this area butwas not responsible for the anomalously Fe-rich nature of somexenoliths from the Kostal Lake eruptive center. 相似文献
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通过详细的岩相学和锆石U-Pb年龄的研究，秘鲁海岸岩基带阿雷基帕段的填图工作得到了补充，该岩基带岩浆活动可分为7个阶段和4个旋回，各阶段都显示出不同的岩浆容量，其地貌主要表现为岩基和岩脉。旋回Ⅰ和旋回Ⅱ代表侏罗纪岩浆活动阶段（201~145Ma），岩浆分异为辉长岩到花岗岩；旋回Ⅲ和旋回Ⅳ代表白垩纪岩浆，岩浆分异为英云闪长岩-二长花岗岩、闪长岩与花岗闪长岩及英云闪长岩-花岗闪长岩。对角闪石和黑云母矿物晶体的数量关系研究表明，旋回Ⅰ的侵入岩有大量辉石和角闪石结晶，并伴随金-铁成矿作用；旋回Ⅱ有大量的群集角闪石晶体和呈定向排列或群集的六边形黑云母，且伴随铜-金-铁成矿作用；旋回Ⅲ侵入岩内发育角闪石和黑云母，伴随着金-铜和铁成矿作用；旋回Ⅳ发育大量角闪石和六边形黑云母，岩石更偏长英质，并伴随铜-锌-金-银-铁和铜-金-钼成矿作用。 相似文献
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Intensive Variables in Kimberlite Magmas, Lac de Gras, Canada and Implications for Diamond Survival 总被引：4，自引：4，他引：4
Crystallization temperatures (T) and oxygen fugacities (fO2)of kimberlite magma are estimated from oxides included in olivinephenocrysts from the Leslie, Aaron, Grizzly and Torrie kimberlitepipes in the central Slave Province, Canada. Crystallizationtemperatures recorded by olivine–chromite pairs at anassumed pressure of 1·0 GPa are 1030–1170°C± 50°C, with a mean of 相似文献
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