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.