Zhuang RUAN¹, Bingsong YU¹, Jia MA² & Yinlu PAN^1
1State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Beijing 100083, China. Ruanz0103@cugb.edu.cn
²Beijing Research Institute of Chemical Engineering and Metallurgy, CNNC, Beijing 101149, China.

STRUCTURALLY CONTROLLED DEEP HYDROTHERMAL TRANSFORMATION OF ORDOVICIAN CARBONATE RESERVOIRS, CENTRAL TARIM BASIN, NW CHINA

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Ordovician carbonate rock is an important hydrocarbon reservoir in the Tarim Basin of NW China. Secondary reservoir space and cementation are related to deep fluid activity, particularly magmatic hydrothermal fluid. Classification and modeling of the magmatic hydrothermal fluids is important in the identification of high-grade reservoirs. The presence of many anomalously a high-temperature fluid inclusion is indicative of significant hydrothermal activity. Samples from both filling (carbonate or other minerals filled in cracks and dissolution holes of carbonate rocks) and country rocks were collected and their C, O, and Sr isotope ratios analyzed. Filling samples were found to have low δ¹³C and δ¹⁸O values, and high ⁸⁷Sr/⁸⁶Sr values. These samples are distinct from the country rocks and other filling samples, indicating the presence of magmatic hydrothermal fluids. Trace element abundance was analyzed in 11 filling samples, yielding positive Eu anomalies and high Th/U values in some samples. Conduit systems such as unconformities, faults, and cracks limit the distribution of hydrothermal fluid and give it a distinct trace elemental and isotopic signature. The hydrothermal fluid derived from magmatic activity may have caused dissolution, cementation, and an increase in the formation fluid temperature.