Chemical Compositions Of Volatiles In Ultramafic Rock In The Main Hole Of Chinese Continenal Science Drilling

The drill site of the Chinese Continenal Science Drilling (CCSD) is located at the southern segment of the Sulu UHP metamorphic belt (N34°25',E118°40'), about 17 km southwest of Donghai Town. The CCSD project provides an advent - ageous and rare chance for collecting UHP rock samples continuously from the subsurface with a depth of more than 5000 m. Samples in the Main Hole of CCSD, Core rocks in the Main Hole of CCSD provide us precious samples by which we can study on ultrahigh-pressure (UHP) metamorphic fluid geochemistry. Fluid compositions of in the subduct—crash—revert zone, exsiting in the Ultramafic Rocks in different conditions, provides us scientific basis to study the geological machism. This paper is about the study of fliud chemical compositions of Utramafic rock in the main hole of the CCSD. An online vacuum stepwise—heating MAT-271 mass spectrometer system was employed to determine the chemical compositions of samples. Conclusions drawn from the study are as follow: (1) The volatiles released from minerals of Mafic Utrahigh mafic rock are dominated by CO₂and H₂, with trace amounts of SO-2 and N₂. (2) The volatiles released from minerals are vary with the types of rock, mineral and the releasing temperature. The volatiles released from quartzs are lowest as an average of 19.25mm³/g. On contrary, the volatiles released from olivine are highest as an average of 41.97mm³/g. The orthopyroxene released higher volatiles as an average of 31.41mm³/g. (3) We got a volatiles release peak as a mean of 33.96mm³/ g from olivine at 500°C,the volatiles at this temperature may be the survivals of the ultrahigh-pressure (UHP) metamorphic substance. The volatiles released from quartzs and olivine are dominated in ultrahigh-pressure (UHP) metamorphic process and less volatiles were got afer that.Above of all, fluid chemical Compositions of ultramafic rock in the main hole of the Chinese Continenal Science Drilling are similar to the fluid compositions of complex mantle in Su-Lu-Wan region (After Zhang,2004,2005) ,and the UHP metamorphic fluids were formed in UHP metamorphism as the UHP metamorphic rock reverted to the surface of earth. This study have shown that fluids did exist during UHP metamorphism, and that the fluid compositions are highly variable from different minerals at different temperature, so the UHP metamorphic fluids were not formed at the same time.