Beschreibung:
The solubility of carbon in forsterite, enstatite, diopside, pyrope and MgAl2O4 spinel has been quantified. Previously reported problems of contamination and slow diffusion of carbon in minerals have been overcome by (1) growing carbon-saturated crystals from carbonatite melts in piston-cylinder (T=900-1100 ʿC; P=1.5 GPa) and multianvil (T=900-1400 ʿC; P=6-11 GPa) experiments in the presence of ~1 wt.% water and by (2) using starting materials, isotopically enriched to contain ~99 wt.% of 13C. Secondary ion mass spectrometry (SIMS) was employed to measure the carbon contents of the synthesized minerals.Carbon solubility in silicates at uppermost mantle conditions is exceedingly low, in the order of a few hundred parts per billion by weight. Solubility increases exponentially as a function of pressure to a maximum of ~12 ppm by weight in forsterite at 11 GPa and 1200 ʿC. No clear dependence of carbon solubility on temperature, oxygen fugacity and iron content was observed. Carbon solubility in MgAl2O4 spinel is below the limit of detection of the analytical technique used (i.e., below 30 ppb by weight).