流体-超镁铁质岩相互作用与硬玉岩的形成

Fluid-Ultramafic Rock Interaction and Formation of Jadeite Rocks

俯冲带中流体与岩石相互作用以及流体循环一直是地质学家关注的焦点之一.硬玉岩(翡翠)作为高档宝玉石材料,其成因一直备受关注.硬玉岩产于与俯冲带有关的蛇纹石化超镁铁质岩中,是俯冲带中流体与超镁铁岩相互作用的特殊产物.岩石组合、岩相学、显微结构及矿物化学特征表明:橄榄岩与流体的作用可以分为5个阶段,分别为蛇纹石化→(绿泥石、金云母)→角闪石→辉石→(方沸石、钠长石)阶段.结合热力学相图,总结了橄榄岩与流体作用过程中矿物的演化序列.硬玉岩的形成需要富Na、Al、Si流体和较高的压力.缅甸硬玉岩中,钠质闪石总是与硬玉岩伴生,钠质闪石成分变化大,且能与流体发生再平衡从而调节自身和流体的成分.钠质闪石在硬玉形成过程中充当了Na、Al、Si的缓冲剂,使Na、Al、Si达到一定比例有利于硬玉的结晶.

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.