Trace element partitioning in immiscible silicate-carbonate liquid systems: An initial experimental study using a centrifuge autoclave

The origin of carbonatites remains a contentious topic. However, an important role for liquid immiscibility between silicate and carbonate liquids has often been proposed. To understand and constrain the role this process may play, it is important to have trace element partitioning data available. Few experimental studies on trace element partitioning between silicate and carbonate liquids have been undertaken, reflecting both analytical and experimental difficulties. To achieve better phase separation new two-liquid experiments have been performed utilizing the rotating centrifuge autoclave. Trace elements in the run products were analysed in situ using laser ablation microprobe-inductively coupled plasma mass spectrometry. Partition coefficients (D) have been determined for selected rare earth elements (La, Nd, Sm, Tb, Er, Tm), high field strength elements (Zr, Hf, Nb, Ta), and for Sr, Ba and Y. Most of the rare earth elements partition preferentially into the silicate liquid. La, Sr and Ba, however, strongly partition into the carbonate liquid. The high field strength elements, although all preferentially partitioning into the silicate liquid, are characterized by a wide range of D values. Zr and Hf have similar D values, which are one to two orders of magnitude lower than those of Nb, Ta and Ti. Ti and Nb behave similarly, whereas Ta demonstrates behaviour intermediate to that of Zr and Hf. Nb/Ta ratios are strongly fractionated by two-liquid partitioning.