Oil & Gas Geology ›› 2008, Vol. 29 ›› Issue (2): 217-222.doi: 10.11743/ogg20080210

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Hydrothermal fluid activity and thermochemical sulfate reduction in the Upper Ordovician,Tazhong area

Li Kaikai1,2, Cai Chunfang1,2, Cai Liulu1,2, Zhang Chunming3   

  1. 1. Key Laboratory of Mineral Resources, Chinese Academy of Sciences, Beijing 100029, China;
    2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;
    3. Geochemistry Department, Yangtze University, Jingzhou, Hubei 434023, China
  • Received:2008-02-13 Online:2008-04-24 Published:2012-01-16

Abstract:

Measurements of rare earth elements,value of 87Sr/86Sr,and fluid inclusion,had been carried out on facture-filling minerals(such as calcite,fluorite and barite) in Tazhong area.Results show that the 87Sr/86Sr va-lues of all the filling minerals(0.708 89-0.710 36) and formation water are higher than that of the whole-rock samples of fracture-carbonate rock and sea water in the same period,and the homogenization temperature of fluid inclusion is about 20℃ higher than that of the highest temperature ever experienced by the Upper Ordovician,signaling the presence of hydrothermal fluid and a high concentration of 87Sr.The hydrothermal fluid with high 87Sr/86Sr value is most likely derived from the Cambrian or pre-Cambrian clastic rocks.Its Eu2+ and Sr2+ are of similar origin,resulting in a positive Eu anomaly and a good linear relationship between Eu and Sr in the fracture fillings.It induced TSR and generated HSS and pyrite.Consequently,the process led to the replacement of barite by calcite.The presence of fracture-filling 87Sr-rich fluorite with relatively low temperature and low salinity as indicates that beside the influence of hydrothermal fluid,the area might also be affected by fresh water and basin fluid of low temperature.

Key words: rare earth element, Eu anomaly, hydrothermal fluid, thermochemical sulfate reduction, Tazhong area

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