MEGAN ROHRSSEN
High pressure high temperature experiments were performed to examine the effect of secondary minerals on grain growth of olivine aggregates. Grain growth of olivine in the mantle has a critical influence on a range of mantle transport properties, including viscosity, electrical conductivity, and chemical diffusivity. The upper mantle consists of ~60% olivine and ~40% other phases, including pyroxenes and aluminous minerals. However, previous experimental studies of olivine grain growth have been performed with 100% olivine (i.e., dunite). High pressure experiments were performed in a piston cylinder apparatus at 2 GPa and 1000, 1200, and 1400 °C for durations ranging from 1 to 96 hours. Experimental charges had two layers - the first consisting of 100% olivine, the second with 60% olivine (ol) , 40% orthopyroxene (opx). Experimental charges were polished and examined by optical and electron microscopy to measure grain sizes of olivine and orthopyroxene. Average grain sizes in ol+opx aggregates were found to be greatly retarded relative to those in pure olivine samples. Efforts to quantify grain growth in these samples are continuing.