IR Spectroscopy of Olivine from Kimberlitic Magma

Abstract

Olivine, the most common mineral in the upper mantle, represents a major component in most mafic magmas. Olivine crystals derived from mantle xenoliths contain hydroxyl impurities and are thought to represent the major reservoir for water in the high-pressure mantle environment. However, olivine crystals sampled from tholeiitic basalts do not contain measurable water. Non-stoichiometric water is observed in a variety of nominally anhydrous crustal minerals, such as quartz and feldspar. Incorporation of water into these minerals is generally attributed to kinetic effects associated with non-equilibrium growth. Silica-poor magmas are typically volatile-rich and have extremely low viscosities promoting rapid crystal growth during transport and emplacement. The purpose of this study was to test the hypothesis that olivine crystals formed in silica-undersaturated, water-rich magmas incorporate measurable hydrous impurities due to their rapid growth.