Kinetics of melt-rock reaction with applications to melt transport in the Earth's mantle and the lunar crust.

摘要

Melt migration in the Earth's mantle and the Lunar crust were explored through experiments, field measurements and numerical modeling. A series of harzburgite and lherzolite dissolution experiments were conducted in basaltic melts. The experiments result in the formation distinct mineralogical zones including dunite from harzburgite, and dunite and harzburgite from lherzolite, each separated by a sharp interface. Composition profiles are observed in both melt and coexisting solids extending across the entire sequence of mineralogical zones. The growth of the mineralogical zones and the composition profiles are rate limited by diffusion in the melt. Building on the experimental results a field study was conducted at the Josephine ophiolite in southern Oregon and the Trinity ophiolite in northern California. At each ophiolite a detailed transect was collected across a dunite body and the host peridotite lithologies. Both transects revealed composition profiles qualitatively similar to those resulting from the harzburgite and lherzolite dissolution experiments. Simple 2-D numerical simulations were used to explore the effects of melt flow on the composition of dunite and host peridotite lithologies. The Josephine profile is consistent with simulations including a component of melt flow from the harzburgite into the dunite. In contrast, the Trinity profile is consistent with simulations including a component of melt flow from the dunite into the surrounding lithologies. The techniques developed and used to explore melt flow in the Earth's mantle also apply to the other terrestrial planets. A series of anorthosite dissolution experiments were conducted to explore the interaction of the lunar picritic magmas and the anorthite rich lunar crust as a function of temperature. Relative to terrestrial studies, the anorthosite dissolution rates are fast. Experiments dissolving anorthosite into an olivine saturated picritic magma result in both a spinel + melt region next to the anorthosite and a crystal free region from the olivine saturated melt. Part of the chemical variability of the lunar picritic magmas can be explained by anorthosite dissolution.