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- Title
柴达木盆地东坪气田氦源岩成因 及其对天然气藏中氦气的影响.
- Authors
刘 军; 王 波; 周 飞; 秦 臻; 刘雨桐; 马东正; 陶辉飞
- Abstract
Dongping granite in the northwest margin of Qaidam Basin is of great value in regional geological evo‐lution research and resource development. Therefore, the geochemical characteristics and zircon U-Pb chronolo‐gy of Dongping granite are analyzed. Dongping granite can be divided into two types. The first type is Adakitic granite with high Sr and low Yb, which has the geochemical characteristics of Adakitic rock. There are garnet, rutile and amphibolite residues in the source area, and no or only a small amount of plagioclase residue. It is speculated that the rock may be formed by partial melting of rutile-bearing eclogite in the thickened lower crust, with melting depth greater than 50 km. The other type is Himalayan type granite with low Sr and low Yb, and the residual facies in the source area are garnet, amphibolite and plagioclase, which may be formed by partial melting of granulite in the thickened lower crust, and the melting depth is about 40-50 km. LA-ICP-MS zircon U-Pb dating results show that the crystallization age of the two types of granites is about 418 Ma, which is the result of the same magmatic activity, and the tectonic discrimination diagram shows that both types of granites belong to the same collision granite. Based on previous research results, this paper believes that at about 418 Ma, the “Southern Altyn Ocean” has been closed, and turned to the stage of intracontinental subduction collision orogeny, resulting in the mutual overlap and thickening of the crust. As the thickened lower crust is heated by the underplating of mantle materials, partial melting occurs at different depths, forming two different types of granites in Dongping. The origin and content of helium in Dongping and its adjacent Jianbei and Niudong gas fields are closely related to the basement granite. Specifically, helium is mainly produced by the decay of U, Th and other radioactive elements in the basement granite and granite gneiss. The longer the basement granitoid body is formed, the higher the helium content in the gas field. Under the background of collision orogenic structure, the granite formed by partial melting of pure crustal materials has higher U and Th contents and stronger helium generation potential.
- Subjects
RADIOACTIVE elements; GAS fields; ECLOGITE; PLAGIOCLASE; GRANULITE; ADAKITE; RUTILE; NEODYMIUM isotopes
- Publication
Natural Gas Geoscience, 2023, Vol 34, Issue 4, p601
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2022.12.011