Two-liquid partition coefficients: Experimental data and geochemical implications |
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| Authors: | E Bruce Watson |
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| Institution: | (1) Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts, USA |
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| Abstract: | Partition coefficients for Cs, Ba, Sr, Ca, Mg, La, Sm, Lu, Mn, Ti, Cr, Ta, Zr, and P between immiscible basic and acidic liquids in the system K2O-Al2O3-FeO-SiO2 were experimentally determined at 1,180 °C and 1 atm. Phosphorus is most strongly enriched in the basic melt (by a factor of 10), followed by rare earth elements, Ta, Ca, Cr, Ti, Mn, Zr, Mg, Sr, and Ba (enriched by a factor of 1.5). Of the elements studied, only Cs is enriched in the acidic melt. The two-liquid partition coefficients of Zr, Ta, Sm, and Mn are constant for concentrations ranging from <0.1% to as high as 1 wt.-%, suggesting that Henry's law is applicable in silicate melts (at least for these elements) to concentrations well above typical trace element levels in rocks. The strong relative preference of many elements for the basic melt implies that the structural characteristics of basic melts more readily permit stable coordination of cations by oxygen. Partitioning of elements between crystal and liquid in a magma must therefore be influenced by the composition (and consequent structure) of the liquid.Application of the two-liquid partition coefficients to possible occurrences of liquid immiscibility in magmas reveals that typical basalt-rhyolite associations are probably not generated by two-liquid phase separation. However, liquid immiscibility cannot be discounted as a possible origin for lamprophyric rocks containing felsic segregations. |
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