Geochemical significance of silicon-bearing rutile in eclogites from Dabie-Sulu ultrahigh pressure metamorphic terrane

This paper reports the geochemical characteristics of silicon-bearing rutiles in ultra-high pressure metamorphic (UHPM) eclogites sampled from Dabie-Sulu orogen. Detailed petrography and trace elements of rutiles from Shuanghe and Donghai analyzed by LA-ICP-MS show that the silicon contents in both intergranular rutiles and rutile inclusions are mostly over 400 ppm. In addition, Si-bearing rutiles occur extensively in UHP metamorphic rocks from different areas of Dabie-Sulu. Mapping of NanoSIMS shows that silicon exists in rutile as homogenous pattern, rather than the silicate or quartz micro-inclusions reported in literatures. Thus we suggest that substitution of Si for Ti leads to the homogenous distribution of silicon which is 6-fold coordinated (same as Ti) in rutile. High temperature and pressure due to continental subduction promote the substitution of silicon for titanium, and the substitution may not take place at supergene environment. Rutiles with high-Si content in metamorphic rocks may trace UHP metamorphism. Therefore, Si-in-rutile perhaps could trace the form and metallicity of silicon in deep earth and estimate the depth of continental subduction.