High-pressure experimental investigations of the melting systematics of compositionally variable peridotites and the electrical conductivity of partially-molten peridotite.

摘要

This dissertation presents the results of three experimental projects utilizing the piston-cylinder apparatus to simulate the high pressure and temperature conditions in the Earth's upper mantle. All three projects use natural mineral separates from spinel lherzolite xenoliths, which were mixed in different proportions to create the starting materials. The first project investigates the melting systematics of modally variable, compositionally intermediate peridotites at 10 kbar. The second project is designed to measure the electrical conductivity of partially molten peridotite at 10 kbar. The third project aims at determining the near-solidus melting systematics of compositionally fertile mantle compositions at 20 and 30 kbar.; The second project uses open synthetic forsterite capsules with Pt/Rh electrodes above and below the sample. A controlled voltage is passed through the sample and digital signal processing techniques are used to determine the electrical conductivity of the partially-molten sample.; The first and third projects use sealed, graphite-lined Pt capsules to contain the peridotite starting materials. The problems of quench crystal growth and consequent modification of low melt fraction glass compositions are dealt with differently in the two projects. The first project uses vitreous carbon spheres as a melt sink to pull the melt from the crystal nucleation sites in the residual peridotite and the third project uses the microsandwich technique to force a higher melt fraction in the peridotite. Mass balance calculations are used to determine the melt fraction and mineral mode of the experiments.; The experimental results from the first project are compared with results from a companion study on fertile peridotites performed at 10 kbar. Experiments for the third project utilize the same starting materials as the aforementioned companion study and provide the foundation for future work. The results will be combined with the companion study to create a polybaric data set for two fertile peridotite compositions. This dissertation includes co-authored material currently in review.