Enrichment of incompatible elements at grain-boundaries of olivine in an olivine-nephelinite.
Enrichment of incompatible elements at grain-boundaries of olivine in an olivine-nephelinite.
复制标题
橄榄石霞石中橄榄石晶界处不相容元素的富集。
DOI：
10.2343/geochemj.20.17
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发表时间：
1986
影响因子：
0.8
通讯作者：
Kazuhiro Suzuki
中科院分区：
文献类型：
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作者：
Kazuhiro Suzuki
用电子探针研究了橄榄石-辉石中橄榄石斑晶亚晶界及亚晶界附近微量元素浓度的变化。橄榄石斑晶表现为均匀的核（Fo85），被富铁边缘包围。岩心中Ti含量为160ppm， Al含量为210ppm， Cr含量为170ppm， Na含量为140ppm；岩心亚晶界中Ti含量为350ppm， Al含量为310ppm， Cr含量为490ppm， Na含量为590ppm。橄榄石/体岩浓度比小于1的微量元素（Ti、Al、Cr、La、Ce、Zn、Ca、Na和K）在晶界和解理处富集，而比值大于1的元素（Ni、Mn和Co）的浓度基本不变。不相容元素的晶界富集可以用它们在冷却时的动力学偏析来解释。本文的研究表明，由火山岩的斑晶矿物和基质中的元素浓度得到的分配系数不能完全代表自然界岩浆过程中的元素浓度。当在岩浆过程建模中使用微量元素分区时，这一点很重要。
Variations in the concentrations of trace elements at and near the subgrain-boundaries within olivine phenocrysts in an olivine-nephelinite were inspected with an electron microprobe. The olivine phenocrysts show homogeneous core (Fo85) surrounded by the Fe-richer rim. The core contains 160ppm Ti, 210ppm Al, 170ppm Cr and 140ppm Na, whereas the subgrain-boundary in the core contains 350ppm Ti, 310ppm Al, 490ppm Cr and 590ppm Na. The trace elements with their olivine/bulk-rock concentration ratios smaller than unity (i.e., Ti, Al, Cr, La, Ce, Zn, Ca, Na and K) are enriched at grain-boundaries and cleavages, whereas the concentrations of elements with the ratios larger than unity (i.e., Ni, Mn and Co) are approximately constant. The grain-boundary enrichment of the incompatible elements can be explained in terms of their kinetic segregation on cooling. The present study suggests that the partition coefficients obtained from element concentrations in the phenocrystic minerals and matrix of volcanic rocks do not essentially represent those in magmatic processes in nature. This is important when partitions of trace elements are used in modeling magmatic processes.