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 importa nt 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. F ew experimental studies on trace element partitioning between silicate and carbonate liquids have been undertaken, reflecting both analytical and expe rimental difficulties. To achieve better phase separation new two-liquid ex periments have been performed utilizing the rotating centrifuge autoclave. Trace elements in the rune products were analysed in situ using laser ablat ion microprobe-inductively coupled plasma mass spectrometry. Partition coef ficients (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 t he silicate liquid. La, Sr and Ba, however, strongly partition into the car bonate liquid. The high field strength elements, although all preferentiall y 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 o f 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.