Supercritical Geofluids and Genesis of Jadeite Jade

Supercritical geofluids are intermediate fluids formed in silicate mineral (rock)-H₂O systems under high temperature and high pressure, whose chemical compositions are between aqueous fluids and magmatic melts. They have strong dissolution, migration and reaction abilities, and are important carriers and mediums for material circulation in the earth. The traditional theories of regional metamorphic origin, magmatic origin and metasomatic origin of initial jadeite jade (jadeitite) have their respective theoretical bases such as experimental reaction, petrography and petrogenesis, but also have some problems in mineral formation sequence, mineral assemblages and their spatial distribution. The original theory of fluid precipitate and metasomatic replacement has proposed two modes in which constituent minerals of jadeite jade are formed. Among mineral particles of jadeite and omphacite and their aggregates, frequently observed phenomena such as fluid-melt inclusions reveal that the initial jadeite jades (jadeitites) were crystallized from fluid and melt miscible systems. On the basis of the research progress on supercritical geofluids in the field of earth science, combined with the research progress on jadeite jade, this article introduces a formation model of jadeite jade from a supercritical geofluid system: The supercritical geofluid formed in the subduction plate dehydrated and under appropriate temperature and pressure conditions carried the dissolved materials; due to the changes of temperature and pressure and other conditions, the early jadeite jade was formed in the mantle wedge fissure or fracture through crystallization filling and then superimposed metasomatism. The formation model is proposed based on a series of evidence chains such as typical fluid-melt inclusions, strong dissolution remnants, early filling textures and mid-late metasomatic textures, enrichment of high field strength elements, rich and even complex mineral (or solid substance) assemblages, and high-pressure to ultra-high-pressure veins containing indicator minerals. Chromites, the product of magmatism before the formation of early jadeite jade, were dissolved or replaced (during a later stage), provided the source of Cr³⁺ for the green color of jadeite jade. After the formation in the early period, jadeite jades also experienced multi-period geological processes, such as melt action and fluid action (including crystallization and metasomatism) after the separation of supercritical geofluids, deformation, metamorphism and exogenetic action. In order to establish the theoretical system of jadeite jade formation, it is necessary to conduct further research and review on the basis of paying attention to the action period of supercritical geofluids.