Distinct Geochemical Behavior of Water in Olivine between Silicate and Carbonatite Metasomatism

Abstract

Metasomatism by silicate or carbonatite melts can significantly modify the mineral physical and chemical properties, and the hydrogen geochemical behavior during the interaction of olivine and melt remains unclear. In this study, olivine wate content was measured by SIMS on two peridotite xenolith suites. The water content in the silicate-metasomatized olivine increases along with the metasomatism intensity, whereas the opposite trend is present in the carbonatite-metasomatized ones. These results reflect that H enters olivine via silicate metasomatism, whereas it is extracted by carbonatite melts due to its high-water solubility. In addition, as 7Li (more hydrotropic than 6Li) have more similar geochemical behavior to H, 7Li preferentially enter olivine during silicate metasomatism, but remain in the melt during carbonatite metasomatism, resulting in distinct Li isotope behavior during the two different metasomatism. Therefore, the water content of olivine can be used to distinguish metasomatic melts, as well as to explain the δ7Li differentiation.

Keywords

• mantle metasomatism
• silicate melt
• carbonatite melt
• water content in olivine
• lithium isotope