Abstract:

Abstract:  Fluidsaturated experiments were conducted to investigate the partitioning of 12 REE and Y between the phosphorusrich peraluminous melt and coexisting aqueous fluid at 1 kbar and 800 ℃All runs were conducted in coldseal RapidQuench pressure Vessels (RQV, a kind of “externally heated coldseal pressure vessels”) using water as a pressure medium for durations of 144 hoursThe major chemical compositions of the initial and runproduct glasses were determined by EMPA; REE contents of the initial and runproduct glasses were determined by LAICPMS; REE contents of aqueous fluids were analyzed by ICPMSIt shows that the partitioning coefficients of REE (including La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) between aqueous fluid and hydrous melt (Dfluid/melt) vary from 01×10-4 to 199×10-4, and Dfluid/meltY range from 02×10-4 to 78×10-4, indicating that REE and Y are preferentially partitioned into the hydrous meltsThe relationship of the fluidmelt partitioning coefficients of REEs to the phosphorus contents in the runproduct glasses shows a nearnormal distribution as the contents of P2O5increasing from 019 wt％ to 609 wt％, with the maximum Dfluid/melt corresponding to 144 wt％ of P2O5The fluidmelt REE partitioning coefficients decrease as increasing the atomic numbers of  REE from La to Lu, showing DLREE>DMREE>DHREEgenerallyThe ratios of DY to DHo show no obvious variations with increasing P2O5 contents in the runproduct glasses from 019 wt％ to 609 wt％, keeping a nearly constant value of ～1 (in the range of 091128)The experimental results demonstrate that the interaction of phosphorusrich peraluminous melt with coexisting aqueous fluid could not result in the fractionation between Y and Ho, and among the REEs.Therefore, it is implied that the meltfluid interaction cannot be a candidate for the mechanism of REE tetrad effect during the evolution of peraluminous magmatic system.

Key words:

Key words: partitioning coefficient; meltfluid interaction; phosphorusrich magmatic system; hightemperature and highpressure experiment