Rapid-quench multi-anvil technique and its application to water partitioning study

Abstract:

Water in the Earth's upper mantle is predominantly stored in nominally anhydrous minerals (NAMs). Since incorporated water has a strong influence on mantle properties, namely melting temperature, rheology, electrical conductivity and seismic velocity, it is important to know the distribution of water among phases. Additionally, knowledge of how water partitions between upper mantle minerals and melts is essential for estimation of water content in incipient melts at different depths, water transport by these melts, and total amount of water in the upper mantle.

There are quite a few studies reporting data on water partitioning between NAMs and melts. The most challenging part of these studies is to quench melt coexisting with mineral phases to form glass at elevated pressures (>2 GPa), which is necessary to measure water partitioning with high accuracy. The difficulty of quenching melt into glass lies in the insufficient cooling rate. Previous studies produced olivine, which is the most abundant mineral in the upper mantle, coexisting with quenched melt up to only 2 GPa (except single experiment at 3 GPa). As a result, there is no systematic pressure, temperature and water content dependence of water partitioning due to the data scattered over the narrow pressure range.

In this study we present the new rapid-cooling technique [Bondar et al., 2020] which allows very high quenching rates of 6000-7000°C/sec, which are more than 1 order of magnitude higher than regular piston cylinder (130°C/sec) and multi-anvil apparatus (650°C/sec) (fig. 1). This technique includes a low thermal-inertia assembly and an external cooling system. To date, we were able to get completely transparent hydrous (2 wt.% H2O by FTIR) peridotite glass coexisting with olivine in 5 melting experiments at pressures from 2 to 6 GPa respectively, with Kilbourne Hole fertile spinel peridotite (KLB-1) as starting composition. We plan to improve the fast quenching technique to quench melts under even higher pressure.