No direct effect of F, Cl and P on REE partitioning between carbonate and alkaline silicate melts

Abstract

This study presents new insights into the effects of halogens (F and Cl) and phosphorous (P) on rare earth element (REE) partitioning between carbonatite and alkaline silicate melts. F, Cl and P are elements that are abundant in carbonatites and alkaline magmatic systems and they are considered to play an important role on the REE behaviour. Nonetheless, their effect on REE partitioning between carbonate and alkaline silicate melts has not yet been constrained.Here we present new experimental data on REE partitioning between carbonate and alkaline silicate melts doped in F, Cl and P, in order to (1) test the Nabyl et al. [2020] REE partitioning model in F-, Cl-and P-rich systems, and (2) identify the possible role of F, Cl and P in carbonate melt REE enrichments during alkaline-carbonatite magma differentiation. The experiments were performed at 850-1050 °C and 0.8 GPa using piston-cylinder devices. Starting materials consisted of carbonatite and phonolite compositions ± doped in F, Cl and P. The experimental results show that REE partitioning is similar in F-Cl-P-rich and -poor systems. The silicate melt composition and its molecular structure (i.e. SiO 2 contents, the alumina saturation index and the alkali/alkaline-earth element ratio), which have already been identified as controlling REE partitioning in F-, Cl-and P-poor systems, still operate in doped systems. No direct effect of the F, Cl or P melt concentrations on REE partitioning has been identified. We also propose an application to natural systems.

Systematic study of high field strength elements during liquid immiscibility between carbonatitic melt and silicate melt

“…However, no clear correlation between 𝐷 𝐻𝐹𝑆𝐸 𝐶𝑀/𝑆𝐿 and the concentration of Fand SO 4 2in the carbonatitic melt has been observed so far, as can be seen in Supplementary Figure S4. This lack of correlation is consistent with previous findings (Nabyl et al, 2021). HFSEs tend to concentrate in silicate melts (𝐷 𝐻𝐹𝑆𝐸 𝐶𝑀/𝑆𝐿 < 1), which can coexist with both F -/SO 4 2--rich and F -/SO 4 2--poor experimental runs.…”

“…Both our experiments and previous partitioning experiments have demonstrated that immiscibility processes between silicate and carbonatitic melts can result in the depletion of HFSEs in carbonatitic melts, depending on varying temperature, pressure, and compositional conditions (Martin et al, 2013;Nabyl et al, 2020;Veksler et al, 1998;Veksler et al, 2012). The newly obtained 𝐷 𝐻𝐹𝑆𝐸 𝐶𝑀/𝑆𝐿 in this study are consistent with recent partitioning experiments (Martin et al, 2013;Nabyl et al, 2021;Nabyl et al, 2020), but significantly higher than the experimental results of Veksler and coworkers (Veksler et al, 1998;Veksler et al, 2012). Noteworthy, our experiments show that HFSE partition coefficients essentially vary in response to changes in the melt composition, especially the SiO 2 content (Figure 2).…”

“…immiscibility from runs 1.5-1200-1%F and 1.5-1150-4%S. (Martin et al, 2013;Martin et al, 2012;Nabyl et al, 2021;Nabyl et al, 2020;Veksler et al, 2012). Notably, the scatter plot highlights a clear positive correlation between Si partition coefficient and HFSEs partition coefficient.…”

“…Previous studies shown that the partition coefficients of HFSEs between carbonatitic melts and silicate melts can vary by 1-3 orders of magnitude under different temperature, pressure, oxygen fugacity, and compositions (Martin et al, 2013;Martin et al, 2012;Nabyl et al, 2021;Nabyl et al, 2020;Veksler et al, 1998;Veksler et al, 2012). This limited dataset has resulted in significant uncertainties in estimating the impact of liquid immiscibility on HFSEs.…”

A Global Marine Sediment Compilation and a Cerium Anomaly Perspective on Metasomatized Mantle Sources for REE‐Mineralized Carbonatites

“…First, REE will strongly partition to primary mantle-derived carbonatite melts (Foley et al, 2009). Second, carbonatite melts strongly sequester REE when form by immiscibility (Nabyl et al, 2020(Nabyl et al, , 2021. Third, when a carbonatite melt reaches the upper crust and begins differentiating, REE are highly incompatible and will be strongly enriched in residual brine-melts (Anenburg et al, 2020(Anenburg et al, , 2021.…”