| C-O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis | |
| Tang Hao-Shu; Chen Yan-Jing; Santosh M.; Zhong Hong; Wu Guang; Lai Yong | |
| 2013 | |
| 发表期刊 | Geological Journal
 |
| 卷号 | 48期号:5页码:467-483 |
| 摘要 | The worldwide 2.33-2.06Ga unique positive C-13(carb) excursion has been correlated with the Great Oxidation Event (GOE). The Dashiqiao Formation in the Liaohe Group of the northeastern North China Craton formed at 2.2-2.174Ga and hosts one of the world-class magnesite deposits. Here we present major element and C and O isotope analyses of 22 samples from the Dashiqiao Formation and use the data to evaluate the impact of the GOE in the North China Craton, as well as the genesis of the Dashiqiao giant magnesite deposits. Six dolomitic marble samples from a similar to 600m thick interval with 1.10 +/- 0.04 of MgO/CaO (mol) ratios show higher C-13(PDB) values of 0.6-1.4 parts per thousand (average 1.2 +/- 0.3 parts per thousand) than those of normal marine carbonates over the globe. However, they display lower O-18(SMOW) of 16.4-19.5 parts per thousand (average 18.2 +/- 1.1 parts per thousand) as compared to their contemporaneous counterparts, suggesting that the primary carbonates in the Dashiqiao Formation should possess a positive C-13 anomaly (possibly 4.2 parts per thousand) reflecting the impact of the GOE, and that the C-13 and O-18 values have been depleted in post-sedimentation diagenesis and/or regional metamorphism. The >550m thick magnesite layer in the studied section has MgO/CaO ratios ranging from 4.45-200.00. These rocks show C-13 and O-18 values of 0.1-0.9 parts per thousand and 9.2-16.9 parts per thousand, with average values of 0.4 +/- 0.2 parts per thousand and 13.3 +/- 2.5 parts per thousand, respectively, obviously lower than those of the underlying dolomites. The depletions of C-13 and O-18 in magnesites relative to dolomitic marbles are interpreted to be the result of hydrothermal alteration related to regional metamorphism leading to rock recrystallization and mass exchange. This interpretation is further confirmed from the hanging-wall dolomitic marble and the veinlet-filled magnesite from the ore layer. The former contains mega-crystals of cylindrical talc and has C-13 of -2.6 parts per thousand and O-18 of 14.1 parts per thousand, indicating that a local fluid-rock interaction between (argillaceous) dolomite and (siliceous) hydrothermal fluids poor in C-13 and O-18 resulted in the formation of talc and further depletion both in C-13 and in O-18. The veinlet-filled magnesite yields C-13 and O-18 values of -2.7 parts per thousand and 16.2 parts per thousand, respectively, showing lower C-13 but higher O-18 than those of massive magnesite in the adjacent strata. Our observation thus strongly supports the interpretation that the massive magnesite interacted with low-C-13 fluids which were possibly sourced from meteoric water at low temperature during post-ore time. Thus, the formation of the Dashiqiao magnesite deposits involved primary sedimentation, diagenesis, regional metamorphism, hydrothermal replacement and local post-ore fluid-rock interaction. |
| 学科领域 | 矿床地球化学 |
| 收录类别 | SCI |
| 语种 | 英语 |
| 文献类型 | 期刊论文 |
| 条目标识符 | http://ir.gyig.ac.cn/handle/352002/5024 |
| 专题 | 矿床地球化学国家重点实验室_矿床地球化学国家重点实验室_期刊论文 |
| 推荐引用方式 GB/T 7714 | Tang Hao-Shu,Chen Yan-Jing,Santosh M.,et al. C-O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis[J]. Geological Journal,2013,48(5):467-483. |
| APA | Tang Hao-Shu,Chen Yan-Jing,Santosh M.,Zhong Hong,Wu Guang,&Lai Yong.(2013).C-O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis.Geological Journal,48(5),467-483. |
| MLA | Tang Hao-Shu,et al."C-O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis".Geological Journal 48.5(2013):467-483. |
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