Silica is unlikely to be soluble in upper crustal carbonatite melts

Abstract

A consensus among all experimental studies is that the solubility of silica (SiO2) is low in upper crustal carbonatite melts of below 5 kbar and 1000 °C (mostly much less than 5 wt% SiO2)1,2, in agreement with most natural melt inclusion studies3,4,5,6. Recently, Berndt and Klemme (B&K hereafter) documented haüyne-hosted melt inclusions from the Laacher See volcano exhibiting carbonatite–silicate liquid immiscibility formed at 720–880 °C and 1–2 kbar, with measured carbonatite melt containing high SiO2 (~ 15 wt%), and moderately low Na2O and K2O (combined contents below 8 wt%)7. Their reported silica contents are exceptionally high, never before observed in natural melt inclusions, and never synthesised in experimental studies at upper crustal conditions. If correct, their results significantly increase the permissible silica range contained in natural carbonatite melts, but our results show that their reported composition cannot be liquid, rejecting the existence silica-rich carbonatite melts at these conditions. Show more