Phosphorus partitioning between olivine and melt : An experimental study in the system Mg 2 SiO
Phosphorus partitioning between olivine and melt : An experimental study in the system Mg 2 SiO
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磷在橄榄石和熔体之间的分配：Mg 2 SiO体系中的实验研究
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
Kohn
中科院分区：
文献类型：
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作者：
Thomas;B.;Grant;C.;Kohn
在Mg2SiO4-Ca2Al2Si2O9-NaAlSi3O8-Mg3(PO4)2体系中，采用冷却速率在1 ~ 10℃/h范围内结晶的橄榄石进行分配实验，测量了橄榄石与熔体之间磷的分配。分配系数DP在0.05 ~ 1.41之间变化，受熔体成分的强烈影响，聚合程度越高的熔体分配系数越高。橄榄石中元素丰度的相关性表明，磷取代Si的比例接近1比1，由Mg空位实现电荷平衡；橄榄石中磷与铝的浓度无相关性。要对橄榄石中磷的分带进行定量建模，需要对DP的控制有一个完整的了解，这一分带最近被证明是火成岩橄榄石晶体的共同特征。本研究中观察到的熔体成分的强烈依赖性表明，当生长中的橄榄石晶体的表面成分与熔体处于平衡状态时，熔体中P浓度的变化和DP值的变化都可能导致P在核心到边缘的变化。在天然橄榄石中常见的高P与高Al和高Cr相关的区域必须用平衡生长以外的过程来解释，并且如前所述，这些区域可能与快速生长期间的溶质捕获有关。
The partitioning of phosphorus between olivine and melt was measured by conducting partitioning experiments within the system Mg2SiO4-Ca2Al2Si2O9-NaAlSi3O8-Mg3(PO4)2, using olivines crystallized with cooling rates in the range 1 to 10 °C/h. Partition coefficients, DP, vary from 0.05 to 1.41 and are strongly influenced by melt composition, with high partition coefficients observed for more polymerized melts. Correlations between elemental abundances in the olivines demonstrate that phosphorus substitutes on a near one for one basis for Si, charge-balanced by Mg vacancies; no correlation between P and Al concentration in the olivine was observed. A complete understanding of the controls on DP is required to model quantitatively the zoning of P in olivine that has recently been shown to be a common feature of igneous olivine crystals. The strong melt compositional dependence observed in this study implies that both changing concentrations of P in the melt during fractionation, and changing values of DP can contribute to core-to-rim variations in P when the surface composition of a growing olivine crystal is in equilibrium with the melt. The common observation of zones in natural olivines where high P is correlated with high Al and Cr must be explained by processes other than equilibrium growth and, as suggested previously, such zones are probably related to solute trapping during episodes of rapid growth.