Carbonatite melts, while representing a small fraction of all magmas on Earths, are important constituents of the deep carbon cycle [1]. These melts are very reactive and quickly evolve during their ascent from CO2-rich (CO2 > 30-40 wt %) and SiO2 poor (SiO2 in-situ data with sink/float experiments at 4 GPa and temperature of 1700 K in a Walker-type multi anvil apparatus at Münster University. Both types of experiments showed that Ca/(Mg+Ca) ≈ 0.5 melts with 12 % SiO2 have densities in the range of 2.9 – 3.05 g.cm-3, higher than carbonatites with 0 % SiO2 (see [3,4]), indicating that small amounts of SiO2 increase the density significantly compared to pure carbonatite melts [4]. The implications of this results for the mobility of transitional melts in the upper mantle will be discussed.

[1] Jones et al. (2013) Rev. Min. Geochem. 75, 289.[2] Hammouda & Keshav (2015) Chem. Geol. 418, 171.[3] Ritter et al. (2020) EPSL 533, 116043.[4] Massuyeau et al. (2023) Chem. Geol. 622, 121275.