Fluid Inclusions in Fibrous Diamonds

Most diamonds are metasomatic minerals, which means they grew from fluids or melts that moved through solid mantle rocks and chemically interacted with them. The involvement of fluids was recognized in the early days of diamond research (e.g., Sobolev 1960; Kennedy and Nordie 1968; Meyer and Boyd 1972; Harte et al. 1980) and was mostly attributed to kimberlite melts (either the erupting kimberlite, or a deeper proto-kimberlite composition). Based on Rb–Sr and Sm–Nd systematics of garnet inclusions in diamonds, Richardson et al. (1984) suggested that it involves “introduction and entrapment of asthenosphere-derived alkali, LREE and CO2 enriched interstitial melt, which remained liquid until the time of diamond crystallization”. However, only sporadic reports on the occurrence of alkali-rich mineral inclusions or fluidor melt-inclusions in diamonds were reported at that time. In later years, evidence for such fluids and the metasomatic origin of diamonds accumulated, including, the association of diamonds with other metasomatic minerals and with alteration zones in xenoliths (e.g., Schulze et al. 1996; Anand et al. 2004; Zedgenizov et al. 2018); trace element abundance patterns of garnet and clinopyroxene inclusions in diamonds that point to interaction with, or growth from melts that are extremely enriched in incompatible trace elements (Shimizu and Richardson 1987; Stachel and Harris 1997; Stachel et al. 2004 and references therein) and observations of fluids or melts in microinclusions in diamonds, which are the subject of this review.