Formation of saddle dolomites in Upper Cambrian carbonates, western Tarim Basin (northwest China): Implications for fault-related fluid flow |
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| Authors: | Juntao Zhang Wenxuan Hu Yixiong Qian Xiaolin Wang Jian Cao Jingquan Zhu Qing Li Xiaomin Xie |
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| Institution: | aState Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, 22 Hankou Road, Nanjing 210093, China;bResearch Institute of Exploration and Development, Northwest Branch, SINOPEC, Urumqi 830011, China;cInstitute of Geology and Geophysics, China Academy of Sciences, Beijing 100029, China |
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| Abstract: | The saddle dolomites occur more intensely in cores closely to fault than that in cores far away from the fault in Upper Cambrian carbonate of western Tarim basin, suggesting that formation of the saddle dolomites is likely related to fault-controlled fluid flow. They partially fill in fractures and vugs of replacement dolomite. The saddle dolomites exhibit complex internal textures, commonly consisting of core and cortex. In comparison with the matrix dolomites, the saddle dolomites show lower Sr-content and 87Sr/86Sr ratios, higher Fe- and Mn-content, and more negative δ18O values. Combined with high Th (100–130 °C) of primary fluid inclusions, it is suggested that the saddle dolomites precipitated from hydrothermal fluid derived from the deep evaporite-bearing Middle Cambrian strata, and the magnesium source may be due to dissolution of host dolomite during hydrothermal fluid migration. Fault activity resulted in petrographic and geochemical difference of the core and cortex of the saddle dolomites. The cores precipitated from the formation water mixed by deep brines at the early stage of fault activity, and the cortexes precipitated from the deep fluid with higher temperatures through the Middle Cambrian later. In summary, the formation of the saddle dolomites implies a hydrothermal fluid event related to fault activity, which also resulted in high porosity in Upper Cambrian carbonate in western Tarim Basin. |
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| Keywords: | Saddle dolomite Fault-related fluid flow The Upper Cambrian The western Tarim Basin |
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