Crust-derived potassic fluid in metamorphic microdiamond

A highly potassic COH fluid, with dissolved phosphate, chloride and sulfate/sulfide, was identified as nanometer-size inclusions in metamorphic microdiamonds of Kokchetav dolomite marble and garnet–quartz–pyroxene rock using an analytical electron microscope (AEM) coupled with an energy-dispersive X-ray (EDX) spectrometer. This provides a direct piece of evidence for the formation of metamorphic microdiamonds from such a fluid. Although this crust-derived potassic fluid and the associated solid precipitates are in some respects similar to the fluid inclusions in fibrous/cloudy mantle diamonds, distinct chemical differences exist. This potassic COH fluid, in addition, has the potential to trigger high to ultrahigh-K magmatic and K metasomatic processes in mantle.