The effect of H2O on olivine crystallization in MORB:: Experimental calibration at 200 MPa

Crystallization experiments were conducted at 200 MPa and water-undersaturated conditions to quantify the effect of small amounts of H2O on the crystallization temperature of olivine in basaltic melts (e.g., Mid-Oceanic Ridge Basalts, MORB). The H2O concentrations in the quenched glasses, determined by infrared spectroscopy and Karl-Fischer-Titration, ranged between 0.25 and 4.2 wt% H2O. The dry liquidus temperature was estimated from experiments at 0.1 MPa (H2O-free) and from the known pressure dependence of olivine crystallization temperature. The liquidus temperature depression can be predicted by the empirical equation (T-DRY-T-WET) = 39.69-C-H2O(0.73)(Wt%). The comparison of the experimental results with available crystallization models and empirical methods shows that most of the predicted liquidus temperature depressions differ significantly from that observed in this study.