Fluid-Ultramafic Rock Interaction and Formation of Jadeite Rocks

The fluid-rock interactions and fluid circulations in subduction zone have been a focus for geologists.As a kind of high-grade gem material,the genesis of jadeite rocks attracts an increasing concern.The jadeite rocks generally occur in the serpentinized ultramafic rocks in subduction zones and its formation is related to the interaction between subduction-related fluids and ultramafic rocks(peridotite).Based on rock association,petrography,microstructure and mineral chemical characteristics,the processes of interaction between peridotite and fluid can be divided into five stages,that is,serpentine→(chlorite,phlogopite) →amphibole→pyroxene→(analcime,albite).Combined with analysis of thermodynamic phase diagrams,the evolutionary series of minerals in the processes of interaction are identified.Formation of jadeite requires the fluids enrich in Na,Al,Si and under relatively higher pressure.In the jadeite rocks from Myanmar,the sodium amphiboles with various chemical components are always associated with the jadeite,and rebalance of the amphiboles with fluids can regulate the compositions of minerals and fluids.Sodium amphiboles act as a buffer in the formation process of jade and the jadeite was crystallized when the Na,Al and Si were concentrated to certain percentage.