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 funciton 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.
|Number of pages||6|
|Journal||Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms|
|Publication status||Published - 2 Sep 1995|