大别山超高压变质岩后成合晶矿物中微细流体包裹体的透射电镜研究

TRANSMISSION ELECTRON MICROSCOPY STUDY ON THE FINE FLUID INCLUSIONS IN SYMPLECTITIC MINERALS FROM UHP METAMORPHIC ROCKS AT SHUANGHE OF DABIE MOUNTAINS,CHINA

流体包裹体的研究对于了解地壳岩石的形成条件、构造演化及其动力学过程具有重要意义。利用透射电镜研究了大别山双河地区超高压硬玉石英岩中退变质矿物或后成合晶冠状体矿物(钠长石、霓辉石、绿闪石和磁铁矿)中的纳米-亚微米级流体包裹体特征及其与构造缺陷之间的关系。观察到该类流体包裹体的粒径(约1 nm～200 nm)要比石英中的流体包裹体(约10 nm～350 nm)小得多,一般呈圆形或负晶形分布、有些呈不规则状或小群体分布,其中大多数含H2O包裹体,有些含CO2流体。流体包裹体常与位错、位错网、晶界或亚边界等交生在一起,这些位错及构造缺陷空间构成了非爆裂流体相渗漏的有利通道。在变形钠长石中发现非均匀分布的纳米级(约1 nm～30 nm)水分子团,这种球形状水分子团包体是导致后成合晶矿物水解弱化和塑性变形的重要因素,该类流体和水分子团的存在,加速了岩石的塑性变形和退变质作用的进程。因此,可以反映大别山地区高压变质后的抬升历史。

The research about fluid inclusions has significant implications for understanding the formation condition,tectonic evolution and dynamic process of crustal rocks. Fluid inclusions at a nano-scale to submicron-scale and their relationship with structural defect in retrograde metamor- phic minerals or symplectitic corona minerals （albite, augite-aegirine, taramite and magnetite） from UHP jadeite quartzite at Shuanghe of Dabie Mountains,China,have been investigated by u- sing transmission electron microscopy （TEM）. It has been observed that the size （1 nm-200 nm） of fluid inclusions in such minerals is much smaller than that （10 nm-350 nm） in quartz. Most fluid inclusions are rounded or negative crystal shaped, while some being irregular orgrouped, with H2O or CO2 fluids. The fluid inclusions often intergrow in dislocations, dislocation networks, crystal boundary or subboundaries and so on. These dislocations and structural defect space represent a favorable path for non-crepitative fluid phase leakage. The cluster of water molecules on the nano-scale （1 nm～30 nm） with non-uniform distribution has been discovered in deformed albite. The cluster of water molecules presenting in spherical inclusions in symplectitic minerals directly causes hydrolytic weakening and induces the plastic deformation of symplectitic minerals by dislocations. These fluids and. cluster of water molecules could accelerate the plastic deformation and the retrograde metamorphism course of rocks, which reflecting an uplift history after high-pres- sure （HP） metamorphism at Dabie Mountains.