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SCIENCE CHINA
Earth Sciences
RESEARCH PAPER February 2012 Vol.55 No.2: 183192 doi: 10.1007/s11430-011-4356-1
Primary dolostone formation related to mantle-originated exhalative hydrothermal activities, Permian Yuejingou section, Santanghu area, Xinjiang, NW China
LIU YiQun1*, JIAO Xin1, LI Hong1, YUAN MingSheng2, YANG Wan3, ZHOU XiaoHu1, LIANG Hao2, ZHOU DingWu4, ZHENG ChaoYang1, SUN Qin1 & WANG ShuangShuang1
1 State Key Laboratory of Continental Dynamics, Northwest University, Department of Geology, Northwest University, Xian 710069, China;
2Tu-Ha Oilfield, CNPC, Hami 830002, China;
3Department of Geological Sciences and Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409, USA;
4College of Geological Science & Engineering, Shandong University of Science and Technology, Qingdao 266510, China
Received March 21, 2011; accepted September 18, 2011
The Permian Lucaogou Formation is an important hydrocarbon source rock in the Junggar, Turpan, and Santanghu basins in Xinjiang, NW China. For the first time, dolostones associated with mantle-originated exhalative hydrothermal fluid flows are discovered in Yuejingou section in the Santanghu Basin area. They include dolomicrite, doloarenite, and a small amount of dolorudite, and are finely (0.050.15 cm thick) interlaminated with lime micrite and dolomicritic analcime laminites. Alkali feldspar and analcime grains are common in doloarenite and are interpreted as having been derived from analcime phonolites and peralkaline magmatic rocks. These magmatic fragments were brought up from subsurface by hydrothermal fluid flow and had experienced exhalative brecciation, transport, and deposition on the lake floor. The matrix consists dominantly of dolomite and ankerite smaller than 0.01 mm. The dolostones can be subdivided into four types on the basis of mineral composition and content. The detrital analcime and alkaline feldspar grains and tuff lithics are interpreted as intraclasts, which were deposited in an under-filled starved lake basin. The 18OPDB values of dolostones are 5 to 21.1, and 11.9 on average; the 87Sr/86Sr ratios of dolostones are 0.70457 to 0.706194, and 0.705005 on average. These values, in combination with evidence of multi-episodes of peralkaline extrusion, suggest a mantle origin of the hydrothermal fluids, which may have promoted primary dolomite formation. The fluid from the upper mantle caused serpentinization of ultramafic rocks that intruded into the lower crust to obtain Mg2+ and Fe2+, and injected the ions into the lake water as the Mg and Fe sources for dolomite and ankerite. Hydro-thermal fluids associated...