A proton- and electron-microprobe study of gallium, nickel and zinc distribution in chromian spinel☆
A proton- and electron-microprobe study of gallium, nickel and zinc distribution in chromian spinel☆
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DOI：
10.1016/0024-4937(95)99071-4
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发表时间：
1995-06
期刊：
影响因子：
3.5
通讯作者：
A. D. Paktunc;L. Cabri
中科院分区：
文献类型：
--
作者：
A. D. Paktunc;L. Cabri
用质子探针和电子探针分析了不同地质环境中铬尖晶石中微量元素的变化。铬尖晶石研究包括那些代表蛇绿混杂岩，层状侵入体在大陆地区，阿拉斯加型杂岩，科马提质次火山岩床，硫化镍矿石和变质镁铁质和超镁铁质岩石。镍浓度范围为30至4690 ppm（质子微探针），平均值为943 ppm。镍有利于尖晶石结构中的八面体位点，随着Cr/（Cr + Al + Fe 3+）比的降低而显示出总体增加。铬尖晶石和地幔硅酸盐之间的镍分配似乎主要取决于铬尖晶石的主要元素组成。锌的浓度范围从230到9810 ppm（质子微探针），在500 ppm附近有一个簇。蛇绿岩铬尖晶石显示最低的总锌值。锌水平似乎区分铬铁矿样品中的铬尖晶石与纯橄榄岩或其他岩石类型中作为副铬尖晶石发生的铬尖晶石。铬尖晶石中或附近的硫化物晶粒显示较高的锌浓度。锌，强烈有利于四面体网站，显示与Mg/（Mg + Fe 2+）比的原油负相关性，并出现作为温度的函数而变化。所有的铬尖晶石颗粒分析含有可测量的量的Ga的质子微探针，范围从10到208 ppm。Ga浓度与Cr/（Cr +Al + Fe 3+）比值呈反比关系，Ni与Ga浓度呈粗略的正相关。铬尖晶石和全岩样品中测得的Ga浓度支持Malvin和Drake（1987）的实验矿物-熔体分配系数。与橄榄岩捕虏体、洋中脊玄武岩和洋岛玄武岩相似，Ga与蛇绿质铬尖晶石和大多数层状杂岩中的Al 2 O3具有良好的相关性。蛇绿质铬尖晶石似乎是从成分与上地幔部分熔体相似的熔体中结晶出来的。
Chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation of trace elements in different geological environments. Chromian spinels studied include those representing ophiolitic complexes, layered intrusions in continental areas, Alaskan-type complexes, komatiitic subvolcanic sills, Ni sulfide ores and metamorphosed mafic and ultramafic rocks. Nickel concentrations range from 30 to 4690 ppm (proton microprobe), with a mean value of 943 ppm. Nickel, favouring the octahedral sites in the spinel structure, displays an overall increase with a decrease in the Cr/(Cr + Al + Fe3+) ratio. Nickel partitioning between chromian spinel and mantle silicates appears to be primarily dependent upon the major element composition of the chromian spinel. Zinc concentrations range from 230 to 9810 ppm (proton microprobe), with a cluster around 500 ppm. Ophiolitic chromian spinels display the lowest overall Zn values. Zinc levels appear to discriminate between chromian spinels in chromitite samples from those occurring as accessory chromian spinel in dunites or other rock types. Chromian spinels that are enclosed in or adjacent to sulfide grains display higher concentrations of Zn. Zinc, strongly favouring the tetrahedral sites, displays a crude negative correlation with the Mg/(Mg + Fe2+) ratio and appears to vary as a function of temperature. All the chromian spinel grains analyzed contain measurable quantities of Ga by proton microprobe, ranging from 10 to 208 ppm. There is a reciprocal relationship between the Ga concentration and the Cr/(Cr +Al + Fe3+) ratio and a crude positive correlation between the Ni and Ga concentrations. Measured Ga concentrations in chromian spinel and whole rock samples are supportive of the experimental mineral-melt partition coefficient of Malvin and Drake (1987). Similar to the peridotite xenoliths, mid-ocean ridge basalts and oceanic-island basalts, Ga correlates well with Al2O3in the case of the ophiolitic chromian spinels and most of those representing layered complexes. The ophiolitic chromian spinels seem to have crystallized from melts whose compositions are similar to those of partial melts of the upper mantle.