Low-temperature crystallization of kumdykolite, a polymorph of albite, during mineral carbonation within fluid inclusions in hornblendite from the Dabie orogen, central China

Kumdykolite is a polymorph of albite that has been predominantly identified within crystallized melt inclusions in high-temperature metamorphic rocks. This study reports a new occurrence of kumdykolite that formed during internal mineral carbonation within amphibole-hosted fluid inclusions in postcollisional hornblendite from the Dabie orogen, central China. Amphibole in the hornblendite trapped CO (sub 2) -rich fluid inclusions at magmatic stage, and mineral carbonation, referring to the reaction of mineral rich in divalent cations and CO (sub 2) into carbonate, occurred in situ within the fluid inclusions due to interaction between trapped CO (sub 2) -rich fluids and host amphibole during cooling of the hornblendite. Kumdykolite was produced along with calcite, dolomite, chlorite, talc, a SiO (sub 2) phase (quartz or cristobalite), a TiO (sub 2) phase (rutile or anatase), and mica during internal mineral carbonation within the fluid inclusions. It is estimated that kumdykolite in the fluid inclusions crystallized under near-surface conditions, which are significantly different from the conditions of crystallization proposed in previous studies. It is further inferred that kumdykolite may crystallize metastably across the stability field of albite, and presence of kumdykolite is not indicative of extreme thermobaric and fluid-absent conditions.