THE EFFECT OF TITANIUM ON THE SILICA CONTENT AND ON MINERAL-LIQUID PARTITIONING OF MANTLE-EQUILIBRATED MELTS

Abstract

High pressure, high temperature phase equilibria experiments were performed to investigate the effect of TiO2 on mineral-liquid equilibria for near natural olivine + orthopyroxene-saturated mafic liquids. At 1.2 GPa and 1360°C, and at 2.8 GPa and 1530°C, near-natural picritic basaltic liquids with TiO2 concentrations ranging from 0.4 to 22 wt.% were forced to be in equilibrium with olivine (ol) + orthopyroxene (opx) by adding appropriate quantities of San Carlos olivine with increasing TiO2. Titanium enrichment of the ol + opx saturated mafic liquids results in nearly pressure-independent linear decreases in SiO2 amounting to 0.60 ± 0.04 and 0.56 ± 0.05 wt.% SiO2 per wt.% TiO2 at 1.2 and 2.8 GPa, respectively. Olivine-liquid Fe-Mg KD decreases at 1.2 GPa from 0.33 at 0.4 wt.% TiO2 down to 0.22 at 19 wt.% TiO2. A similar trend, shifted to slightly higher KD values, is observed at 2.8 GPa.