1.中国科学院地质与地球物理研究所北京 100029； |2.中国科学院研究生院北京 100049； |3. Department
of Geology|University of Regina|Regina SK Canada S4S 0A2； |4.中国石化石油勘探开发研究院北京 100083
Characteristics of saddle dolomite cements in the CambrianOrdovician carbonates in Tabei and Tazhong area of Tarim Basin
Wang Dan1,2 Wang Xu1,2 Chen Daizhao1 Yang Changchun1 Hairuo Qing3 Wu Maobing4 Xing Xiujuan4
1.Institute of Geology and Geophysics|Chinese Academy of Science|Beijing 100029； |2.Graduate University of Chinese Academy of Science|Beijing 100049； |3.Department of Geology|University of Regina|Regina|SK|Canada S4S 0A2； 4.Sinopec Petroleum Exploration and Production Institute|Beijing 100083
Detailed researches of CambrianOrdovician dolostones in Tabei and Tazhong areas of Tarim Basin demonstrated widespread presence of saddle dolomite cements，which commonly occur as cements(or infilling)in vugs and/or fractures. These dolomite crystals，generally 500〖CS％0,0,0,0〗〖CS〗μm up to 6 mm in size，are creamy white nonplanar crystals with curved or lobate or stepped crystal faces. They are gappy and sweeping extinction under microscope，commonly associated with other hydrothermal minerals. The saddle dolomites have δ13C values from -2446‰ to 0686‰ PDB，and δ18〖KG-*5〗O values from -9101‰ to -5117‰ PDB，and 87〖KG-*5〗Sr/86〖KG-*5〗Sr ratios from 0708〖CS％0，0，0，0〗〖CS〗6 to 0710〖CS％0，0，0，0〗〖CS〗2. Fluid inclusion micro thermometry data of the saddle dolomites cements indicates homogenization temperatures(Th)of gasliquid inclusions is about 121～1595°C and salinities of dolomitization fluids is about 187％〖KG-*5〗～231％(wt％ NaCl equivalent)from which the saddle dolomites precipitated. These data suggest that the saddle dolomites could have formed in thermal brine. Compared with saddle dolomites of other basins all over the world，the saddle dolomites of Tarim Basin have similar δ13C and δ18〖KG-*5〗O values，but lower 87〖KG-*5〗Sr/86〖KG-*5〗Sr ratios. The reason could be that the saddle dolomites were formed in magmatic hydrothermal，which was mantlederived and reached carbonate formation accompanying igneous intrusion or through discordogenic faults without going through siliciclastic sediments. Thus the saddle dolomites formed from the magmatic hydrothermal have lower 87〖KG-*5〗Sr/86〖KG-*5〗Sr ratios than others.