| Author's Name: ZHAO Jin, FENG Mingyou, SHEN Anjiang, WEN Long, XU Liang, WANG Xingzhi, LIU Xiaohong |
| Institution: School of Geoscience and Technology, Southwest Petroleum University |
| Abstract: |
| Taking the zebra dolomite of the Middle Permian Qixia Formation in Wulong area of Baoxing in Southwestern Sichuan Basin as the research object, the genesis of the dolomite is analyzed by means of petrology and geochemistry. The zebra dolomite in the area is mainly developed in the upper part of the Qixia Member 1, which occurs in parallel or oblique to the layers. The dark and bright bands of zebra texture are composed of powder-fine dolomite with residual fabric and mesocrystalline-megacrystalline saddle dolomite, the cathodoluminescence of which is dark red and bright red respectively, indicating the element difference of growth space and in the process of metasomatism. The order degree of dolomite of zebra texture is low, and the negative anomaly of δ 18 O value is obvious. The 87 Sr / 86 Sr value of the dark band is in or slightly higher than the seawater range of the same period; the obvious higher 87 Sr / 86 Sr value in the bright band indicates the influence of deep fluid. Both the bright band and the dark band have low ∑REE content and obvious positive Eu anomaly. The comprehensive study shows that the formation of zebra dolomite of Qixia Formation in Southwestern Sichuan belongs to hydrothermal metasomatism -crystallization genesis during burial period, which reflects the dynamic balance process between dolomite crystallization force and rock tensile strength under the continuous supply of hydrothermal fluid. The formation of zebra dolomite undergoes three stages: (1) hydrothermal fluids migrate vertically along the basement fault, and magnesium-rich fluids enter in the high porosity and permeability stratum along the bedding, and continuously dissolve and replace the limestone to form dark band dolomite; (2)when the crystallization force
of dolomite is greater than the tensile strength of rock, a series of fractures will be formed; (3)after dissolution, the ions in fluid precipitate to form bright band saddle dolomite in the fracture. |
| Keywords: zebra texture; hydrothermal dolomite; metasomatism-crystallization; Qixia Formation; Permian; Southwest⁃ern Sichuan Basin |
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投稿时间：
2019-12-16 |
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