Raman spectroscopy of hydrous inclusions in olivine and orthopyroxene in ophiolitic harzburgite: Implications for elementary processes in serpentinization

Abstract

Secondary microinclusions in olivine and orthopyroxene in a harzburgite sample obtained from northern Oman ophiolite were examined by micro-Raman spectroscopy. The microinclusions were a consequence of fluid inclusions trapped by the minerals during the healing of fluid-filled cracks. We can expect an almost closed-system reaction to have occurred between the fluid and minerals. We attempted to distinguish the individual contributions of olivine and orthopyroxene to the serpentinization of peridotite. The inclusions in olivine mainly consist of lizardite and brucite with small amounts of magnetite, H2, and CH4, while those in orthopyroxene mainly consist of talc and chromian spinel with or without CH4 and graphite. The fluid involved was most probably a mixture of H2O and a smaller amount of CO2. We examined whether reduced gases were produced through reactions of the fluid with olivine and orthopyroxene. The role of magnetite (or magnetite component in chromian spinel) is of vital importance in the generation of these gases. Orthopyroxene facilitates the formation of talc in the serpentinization of peridotite.