An experimental study of partitioning of fluorine between K-richterite, apatite, phlogopite, and melt at 20 kbar
An experimental study of partitioning of fluorine between K-richterite, apatite, phlogopite, and melt at 20 kbar
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20 kbar 下氟在钾利辉石、磷灰石、金云母和熔体之间分配的实验研究
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发表时间：
1995
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通讯作者：
L. Pizzolato
中科院分区：
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作者：
A. D. Edgar;L. Pizzolato
在20 kbar压力下，主要在含Fe− Ti的含F钾-锂云母-金云母和钾-锂云母-磷灰石体系中的超滑线条件下测定了相关系，以评估上地幔条件下F在金云母、钾-锂云母、磷灰石和熔体中的分配。这两个系统是假三元的，因为它们包含镁橄榄石，顽火辉石和透辉石丰富的单斜辉石从云母和钾-里希特的分解。在相同压力下，含氟钾锂霞石系统的最低熔融温度低于含氟金云母-磷灰石系统。然而，在所研究的系统中，金云母中的F似乎是最有效的成分，在改变最小的液体组合物，而本研究和以前的系统之间的比较表明，在熔化过程中P2 O 5的存在下，可能会导致更多的富K熔体。含F相的组成变化主要受端元矿物的整体组成和温度的控制，尽管非含F矿物（例如单斜辉石）的缓冲可能是有效的。含氟矿物和共存液体之间的分配系数（重量%比）已被确定为整体组成和温度的函数的产品的实验。大多数体相组分的K-锂霞石-液体、磷灰石-液体和金云母-液体之间的分配系数≥1 ~略<1，表明F一般是相容元素。这一结论与超钾质岩石中相似相的F分布序列一致。这些结果排除了在地幔中的含F矿物储层，在对应于20千巴的深度，能够产生富F超钾质岩浆，或有效的氧化还原熔融过程。
Phase relations have been determined at 20 kbar and primarily under suprasolidus conditions in the Fe−Ti-free F-bearing K-richterite—phlogopite and K-richterite—apatite systems in order to assess the partitioning of F among phlogopite, K-richterite, apatite, and melt under upper-mantle conditions. Both systems are pseudoternary because they contain forsterite, enstatite and a diopside-rich clinopyroxene from the breakdown of the mica and K-richterite. The F-bearing K-richterite systems have lower minimum melting temperatures than the F-bearing phlogopite —apatite system at the same pressure. However in the systems studied, F in phlogopite appears the most effective component in altering minimum liquid compositions whereas comparison between the present study and previous systems suggests that the presence of P2O5 during melting may result in more K-enriched melts. Variations in the compositions of the F-bearing phases are primarily controlled by the bulk compositions of the end-member minerals and by temperature, although buffering by non-F bearing minerals (e.g. clinopyroxene) may be effective. Distribution coefficients (as wt% ratios) between F-bearing minerals and coexisting liquids have been determined as functions of bulk composition and temperature for products of experiments. Distribution coefficients between K-richterite—liquid, apatite—liquid, and phlogopite—liquid are ≥1 to slightly <1 for most bulk compositions, indicating thatF is generally a compatible element. This conclusion is in agreement with the sequence ofF distribution for similar phases in ultrapotassic rocks. These results preclude F-bearing mineral reservoirs in the mantle, at depths corresponding to 20 kbar, being capable of producing F-enrichment in ultrapotassic magmas, or being effective in redox melting processes.