Immiscible silicate liquids at high pressure: The influence of melt structure on elemental partitioning

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• 作者：Vicenzi ; E.P. ; Green ; T.H. ; Sie ; S.H.
• 刊名：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
• 出版年：1995
• 出版时间：September, 1995
• 年：1995
• 卷：104
• 期：1-4
• 页码：470-475
• 全文大小：789 K

文摘

Immiscible silicate melts in the system SiO₂-FeO-Al₂O₃-K₂O (+P₂O₅) have been stabilised at 0.5 and 1.0 GPa over a temperature range of 1160-1240°C. Unmixing in this system produces one melt rich in SiO₂ and another rich in FeO, and a minor component of β-quartz. A study of partitioning of elements of geochemical interest: Rb, Ba, Pb, Sr, La, Ce, Sm, Ho, Y, Lu, Th, U, Zr, Hf, Nb and Ta between the immiscible silicate melts at trace levels has been made possible by the development of quantitative microbeam PIXE. The trace elements were introduced at approximately 200 ppm level for all elements except for the REEs, Ba and Ta (600-1200 ppm). Trace element partitioning was found to be a complex function of cation field strength (charge/radius²), and in broad terms can be modelled by a third-order polynomial. Although field strength is important in determining the nature and degree of partitioning, it is clearly only one component of the underlying mechanism for the way in which elements distribute themselves between two silicate liquids. Hf partition coefficients were found to approximate unity, and thus its partitioning is nearly independent of the melt composition.