江苏东海水晶矿床成因初探:流体包裹体和硅氧同位素证据

Preliminary study on the genesis of rocked quartz in Donghai, Jiangsu province: evidences from fluid inclusions and Si, O isotope.

东海水晶矿床位于苏鲁超高压变质带中,它的成因机制及其与超高压变质作用的关系一直是大家关注的问题。本文运用流体包裹体、硅氧同位素地球化学以及微量元素地球化学,对东海水晶矿床的成因进行了初步研究。结果显示,舍晶石英脉中流体包裹体主要有单液相、气液两相以及H2O-CO2流体包裹体,其中以气液两相流体包裹体为主,大小在5-50μm,但在含金红石发晶的水晶中气液两相流体包裹体最大可达300μm。其形成温度可以分为3个区间,即100℃-120℃, 160℃-220℃和240℃-260℃;而其盐度也集中于0-2wt％NaCl,4-12wt％NaCl和14-16wt％NaCl三个区间,反映了多期流体的叠加作用。激光拉曼和流体包裹体群成分分析可知,流体包裹体中除了H2O和CO2外,还有N2、CH4、H2S和C2H6等,并且在不同的爆裂温度情况下,流体包裹体所释放的成分有所差别。东海水晶矿床中不含金红石发晶的石英的δ18O变化范围在-5．6～+4．6‰,δ34Si变化范围在-0．2-+0．2‰之间;而含金红石发晶的石英的δ18O变化范围在10．5-14．9‰,δ34 Si变化范围在-0．2-+0．1‰之间。相对来说,与水晶热液作用有关的鳞片状黑云母比斜绿泥石更加富集Nb、Cr、Fe、V、W、Ti和Zr等。本文认为东海水晶矿床的形成在富含石英的榴辉岩在大陆板块俯冲折返过程中及其以后,由不同时期、不同性质、不同成分流体叠加作用下的结果,而含金红石发晶的形成则是叠加富Nb、Fe流体的结果。

Donghai rocked quartz deposit is located in the Su-Lu Ultra-high pressure （UHP） metamorphic zone, Jiangsu province. Its genesis and its relationship with UHP metamorphism remain unclear. Petrographic, microthermometric, and the Laser Raman investigations recognized that there are three types fluid inclusions in rocked quartz, i.e. pure liquid H2O, liquid-vapor H2O and CO2-H2O fluid inclusions, the liquid-vapor H2O fluid inclusions are dominated, it size are range from 5 to 50 μm, but that of liquidvapor H2O fluid inclusions in rutile-bearing rocked quartz are more than 300μm. In additional to H2O and CO2, there are minor N2, CH4, H2S and C2H6 also are detected in the fluid inclusions. In different decrepitation temperature, the fluid inclusions release different gases, for example, in low temperature, H2Oand CO2 were released with minor H2S, CH4 and C2 H6, whereas in high temperature, H2O,CH4 ,C2 H6 and CO2 were released with minor N2 and H2 S. The homogenization temperature and salinity of fluid inclusions in rocked quartz are divided into three sections respectively, i.e. 100℃ -120℃ ,160℃ -220℃ and 240℃ -260℃ and 0 -2 wt% NaC1, 4- 12wt% NaCl, 14 -16wt% NaCl, which reflect multi-stage fluids overprinted in rocked quartz. The δ^18O and B34 Si in quartz range from -5.6 - ＋4. 6‰ and -0. 2 - ＋0. 2‰, respectively, but those in rutile-bearing quartz, are in the range from 10. 5 - 14. 9 and -0.2 - ＋ 0. 1‰, respectively. Contrasted with chlinochlore related to rocked quartz, the scale-biotite is more rich in Nb,Cr,Fe,V,W,Ti and Zr. This paper indicates that rocked quartz deposit in Donghai is related to quartz-bearing eclogite overprinted by different fluids after the exhumation, the rutile-bearing quartz is overprinted by fluids rich in Nb and Ta.