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

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 50μm, but that of liquid-vapor H2 O fluid inclusions in rutile-bearing rocked quartz are more than 300μm. In additional to H2 O 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, H2 Oand CO2 were released with minor H2 S、CH4 and C2 H6, whereas in high temperature, H2O、CH4、C2H6 and CO2 were released with minor N2 and H2S. 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%NaCl, 4 - 12wt%NaCl, 14 - 16wt%NaCl, which reflect multi-stage fluids overprinted in rocked quartz. Theδ18O andδ34Si 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.