INTERACTION OF DIOPSIDE AND JADEITE WITH POTASSIUM CHLORIDE AT 5 GPA

Abstract

The alkali-enriched chloride inclusions found in diamonds and olivines from kimberlites provided new insight into the role of chloride components in the evolution of some mineral assemblages of the upper mantle. In some microinclusions from diamonds, chloride liquid often coexists with minerals of peridotite and eclogite assemblages. Products of reaction between them are observed in several cases. According to the mineralogical thermobarometric data, these reactions proceeded at a pressure of ~5 GPa. The deep-seated eclogite xenoliths also bear indications of the influence of fluids enriched in alkalis and chlorine. The alkali-rich glasses associated with djerfisherite, sodalite, phlogopite, and sanidine are an example. These processes could foster the crystallization of “metasomatic coated diamonds” suggesting a pressure of approximately 4.5–5.0 GPa. The participation of chloride liquids in metasomatic processes in the upper mantle is a highly attractive hypothesis, because these liquids are immiscible with silicate melts at a high pressure but can be a source of alkalis for these melts and a medium for diamond growth.