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Subsolidus phase relations have been determined in the systems SiO2-Cr-O and MgO-SiO2-Cr-O in equilibrium with metallic Cr, at 1100 to 1500℃ and 0 to 2.88 GPa. The results show that there are no ternary phases in the SiO2-Cr-O system at these conditions, i.e., only the assemblage eskolaite-Cr-metal-quartz (or tridymite) is found. In the MgO-containing system, however, extensive substitution of Cr2+ for Mg is observed in (Mg, Cr2+)2SiO4 olivine, (Mg, Cr2+)2Si2O6 pyroxene, and (Mg, Cr2+)Cr2O4 spinel. Cr3+ levels in olivine and pyroxene are below detection limits. The pyroxene is orthohombic at XCrPx2+ < 0.2, monoclinic at higher XCrPx2+ . Thestructure of the spinels becomes tetragonally distorted at XCr2+Sp >0.2. The experimental datahave been fitted to a thermodynamic model, and the authors obtained the mixing parameter (W) of Mg-Cr2+ in olivine, pyroxene and spinel, and the relation between temperatures and free energies of formation for the end-members: Cr2+-olivine (Cr2SiO4), Cr2+-pyroxene (Cr2Si2O6) 相似文献
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锗橄榄石-尖晶石扭转大变形实验研究 总被引:2,自引:0,他引:2
对(Mg,Ni)2GeO4尖晶石一橄榄石集合体进行了高温高压扭转大变形实验研究。试验在一台高分辨率的气体介质试验机上进行,试验温度为1473K,围压为300MPa,应变率为10^-4~10^-5S^-1,剪切应力为80~250MPa,剪切应变为30%~700%。将变形后试件沿轴向切开进行了显微结构分析,确定了两相成分的比值。利用EBSD方法分别对变形前后试件中的橄榄石和尖晶石中的晶格最优取向(LPO)进行了测定,由微结构的差异确定了变形机制及两相材料的相对强度。 相似文献
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