Genesis and geological significance of carbonate in Changdu Basin, Xizang, China: Constraints from geochemistry and C–O isotopes

IF 1.4 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Acta Geochimica Pub Date : 2024-05-27 DOI:10.1007/s11631-024-00704-3

Wenhua Han, Yongshou Li, Haizhou Ma, Huaide Cheng, Binkai Li, Qinyu Hai, Xuahai Ma

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Abstract

Research on the origin of carbonates in Changdu Basin holds significant importance for understanding the regional potash formation model. Based on a comprehensive review of previous studies, field geological surveys, and laboratory investigations, this study analyzes the origin and properties of carbonates within the context of regional potash formation. Petrographic studies show that magnesite deposits, with the characteristics of sedimentary origin. The results of elemental geochemical analysis show that the carbonates in this area were formed in the sedimentary environment via evaporation followed by concentration, and the formation of magnesite was possibly caused by the substitution of calcium in the dolomite with magnesium-rich brine. The δ¹³C values of carbonats in the study area are between 5.9‰ and 9.1‰. The δ¹⁸O values of magnesite samples range from − 7.3‰ to − 1.3‰, and the δ¹⁸O values of dolomites range from − 10.3‰ to − 8.4‰. All the calculated Z values of oxygen isotopes of carbonates greater than 120. A comprehensive analysis of carbon and oxygen isotopes indicates that the magnesite was formed in a highly concentrated Marine sedimentary environment and does not show any relation with the metasomatism of hydrothermal fluids. The results on the correlation of magnesite with seawater and its sedimentary origin provide key information for explaining the migration direction of brine between the Changdu and Lanping–Simao Basins. The residual metamorphic seawater in the Changdu Basin migrated to the Lanping–Simao Basin, where potash underwent deposition. Whereas, magnesite and dolomite in the early stage of potash formation were left in the Changdu Basin.

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中国西藏昌都盆地碳酸盐岩的成因及其地质意义：地球化学和 C-O 同位素的制约因素

昌都盆地碳酸盐岩的成因研究对于理解区域钾盐形成模式具有重要意义。本研究在全面回顾以往研究、野外地质调查和实验室研究的基础上，分析了区域钾盐形成背景下碳酸盐岩的成因和性质。岩石学研究表明，菱镁矿沉积具有沉积成因的特征。元素地球化学分析结果表明，该地区的碳酸盐是在沉积环境中通过蒸发后浓缩形成的，而菱镁矿的形成可能是由于白云岩中的钙被富含镁的盐水所取代。研究区域碳酸盐岩的δ13C值介于5.9‰和9.1‰之间。菱镁矿样品的δ18O值介于-7.3‰至-1.3‰之间，白云岩的δ18O值介于-10.3‰至-8.4‰之间。所有计算得出的碳酸盐氧同位素 Z 值均大于 120。碳和氧同位素的综合分析表明，菱镁矿是在高浓度海洋沉积环境中形成的，与热液的变质作用没有任何关系。菱镁矿与海水的相关性及其沉积成因的研究结果为解释盐水在昌都盆地和兰坪-思茅盆地之间的迁移方向提供了关键信息。昌都盆地的残余变质海水向兰坪-思茅盆地迁移，钾盐在此沉积。而钾盐形成初期的菱镁矿和白云岩则留在了昌都盆地。

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来源期刊

Acta Geochimica GEOCHEMISTRY & GEOPHYSICS-

CiteScore

2.80

自引率

6.20%

发文量

1134

期刊介绍： Acta Geochimica serves as the international forum for essential research on geochemistry, the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth‘s crust, its oceans and the entire Solar System, as well as a number of processes including mantle convection, the formation of planets and the origins of granite and basalt. The journal focuses on, but is not limited to the following aspects: • Cosmochemistry • Mantle Geochemistry • Ore-deposit Geochemistry • Organic Geochemistry • Environmental Geochemistry • Computational Geochemistry • Isotope Geochemistry • NanoGeochemistry All research articles published in this journal have undergone rigorous peer review. In addition to original research articles, Acta Geochimica publishes reviews and short communications, aiming to rapidly disseminate the research results of timely interest, and comprehensive reviews of emerging topics in all the areas of geochemistry.