Genesis of calcite veins in Carboniferous Permian volcanic fractures， northwestern Junggar Basin
Lin Huixi1, Meng Fanchao2, Xu Youde1, Xu Tao1, Cui Yan3
1. Western Branch of Research Institute of Exploration and Development，Shengli Oilfield， SINOPEC，Dongying， Shandong 257000；
2. School of Geosciences， China University of Petroleum， Qingdao, Shandong 266580；
3. College of Earth Science and Engineering，Shandong University of Science and Technology，Qingdao, Shandong 266590
Fractures are well—developed in Carboniferous—Permian volcanic rocks， northwestern Junggar Basin， which are almost filled with calcite. The origin of calcites is revealed by researching on the types of fractures， analyzing the homogenization temperature of primary fluid inclusions and calcite geochemistry data. The result shows that there are four types of fractures in volcanic rocks， weathered fractures， structural fractures， diagenetic fractures and dissolved fractures. Primary fluid inclusions of calcite show a wide range of homogenization temperatures from 40℃ to 150℃， which means that the calcite is related to either hypothermal or epithermal or both. The characteristic of carbon and oxygen isotope composition indicates that the fluids come from meteoric water and buried fluid. The Sr isotope and Mn element confirms that buried fluids are deep—soured hot fluids or fluids with some dissolved volcanic rocks. Affected by the thrust faults of northwestern Junggar Basin and weathering leaching， a large number structural fractures and weathered fissures are formed and connected with each other. The calcite veins in Carboniferous—Permian volcanic rocks are formed with characteristics of meteoric waters and deep—source hot fluids.