Immiscible silicate liquid partition coefficients: implications for crystal-melt element partitioning and basalt petrogenesis

摘要

This study investigates partitioning of elements between immiscible aluminosilicate and boro-silicate liquids using three synthetic mixtures doped with 32 trace elements. In order to get a good spatial separation of immiscible liquids, we employed a high-temperature centrifuge. Experiments were performed at l,050-l,150 deg C, 1 atm, in sealed Fe and Pt containers. Quenched products were analysed by electron micro-probe and LA ICP-MS. Nernst partition coefficients (D's) between the Fe-rich and Si-rich aluminosilicate immiscible liquids are the highest for Zn (3.3) and Pe (2.6) and the lowest for Rb and K (0.4-0.5). The plots of D values against ionic potential Z/r in all the compositions show a convex upward trend, which is typical also for element partitioning between immiscible silicate and salt melts. The results bear upon the speciation and structural position of elements in multicomponent silicate liquids. The ferrobasalt-rhyolite liquid immis-cibility is observed in evolved basaltic magmas, and may play an important role in large gabbroic intrusions, such as Skaergaard, and during the generation of unusual lavas, such as ferropicrites.