摘要
为了研究Ｃｒ^（２＋）在橄榄石、斜方辉石和尖晶石中的溶解度及其在各相间的分配，在压力为０－２．８８ＧＰａ和温度为ｌｌ００－１４５０℃的条件下，于ＭｇＯ－ＳｉＯ_２－Ｃｒ－Ｏ体系中完成了一系列实验。实验起始成分由高纯度的ＭｇＯ、ＳｉＯ_２、Ｃｒ_２Ｏ_３和Ｃｒ混合得到。通过Ｃｒ_２Ｏ_３。和Ｃｒ等化学混合得到所需的ＣｒＯ，且加有过量（５０％）的Ｃｒ，使得实验产物和金属Ｃｒ保持平衡。此外，还加入占起始混合物重量１０％的ＢａＯ＋Ｂ_２Ｏ_３作为流体成分，以保证实验的平衡和有利于晶体的生长。样品容器材料为金属Ｃｒ。实验产物先经粉晶Ｘ射线定性鉴定，再进行电子探针定量分析，然后通过化学计量法算得ＣｒＯ在不同相（橄榄石、斜方辉石、尖晶石）中的含量。结果表明，在橄榄石和斜方辉石中Ｃｒ^（３＋）可忽略不计。实验结果显示：随着温度的升高、压力的降低，Ｃｒ^（２＋）在橄榄石、斜方辉石和尖晶石中的溶解度逐渐增大；随着温度的升高，Ｍｇ－Ｃｒ^（２＋）在橄榄石－斜方辉石之间的分配系数降低，在斜方辉石－尖晶石之间的分配系数增大，而在橄榄石－尖晶石之间的分配系数变化不大。压力对以上各分配系数的影响可忽略不计。
Experiments were performed in the MgO-SiO2-Cr-O system at 0─2.88 GPa and 1100─1450℃,with interests focusing on the solubility of Cr2+ in olivine(Ol), orthopyroxene (Opx) and spinel (Sp) and its partitioning between these phases. Analytical reagent grade chemicals, MgO, SiO2,Cr2O3 and Cr were used to make starting mixes. Cr and Cr2O3 were mixed at stoichiometric ratio to yield the composition CrO.Excess Cr (50%) was then added to these mixtures to ensure that the resulted phases were in equilibrium with metal Cr. Flux of BaO + B2O3 (10%) was added to facilitate experimental equilibrium and growth of crystals. Metal Cr was used as the capsule material. All phases in the product were identified by X-ray and analyzed by electron microprobe. The CrO content (%) in the different phases (Ol,Opx and Sp) was calculated according to stoichiometry. The results indicate that Cr3+ in Ol and Opx is negligible, and that the solubility of Cr2+ in Ol, Opx and SP increases with increasing temperature and decreasing pressure. lnKd(Mg-Cr2+)(Ol-OPX) decreases,and lnKd(Mg-Cr2+)(Opx-Sp), increases with increasing temperature, while lnKd(Mg-Cr2+)(Ol-Sp) doesn't change much. The effect of pressure on all partitioning coefficients is negligible.
出处
《地球化学》
CAS
CSCD
北大核心
1995年第3期235-244,共10页
Geochimica
关键词
铬离子
溶解度
橄榄石
斜方辉石
尖晶石
实验
solubility of Cr￣(2+)
olivine
othopyroxene
spinel
experimental study
