Sinjan Roy , Shiba Shankar Acharya , Ramananda Chakrabarti
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Here, we conduct a systematic attempt to decipher the alteration of the composition of laterite developed over the Rajmahal flood basalt.</p><p>We demonstrate that the chemical index of alteration (CIA) and the mafic index of alteration (MIA) are less effective in deciphering extreme chemical weathering events, where desilication dominates the weathering process. In the weathered residues, the retention of REEs generally follows the trend of light rare earth elements (LREE) > middle rare earth elements (MREE) > heavy rare earth elements (HREE). Except for La and Ce, all other REEs show a depleting trend with reference to the parent rock composition. The ∑REE did not show any significant relationship with the commonly used weathering indices, which shows that the retention of REEs is not a function of the extent of weathering. The covariation of Ce anomaly with the Fe and Mn distribution in the samples reflects a redox-controlled mechanism. The negative correlation between the Eu anomaly and kaolinite abundance suggests that Eu mobilization from parent rock happens during initial weathering phases when plagioclase weathering dominates. The samples show an interesting positive Gd anomaly, which is explained by enhanced retention of Gd than neighboring Eu and Tb. During the chemical weathering of basalt, the retention of Ho was found to be greater than its geochemical twin Y. The results of this study show that significant differences exist between the REEs' distribution of parent basalt and that of the weathered residue, which has implications for the application of REEs as a provenance indicator and/or weathering proxy. The enrichment of Th and U in the weathered samples is explained through the addition of aeolian dust of upper continental crustal composition.</p></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"84 1","pages":"Article 126086"},"PeriodicalIF":2.6000,"publicationDate":"2024-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0009281924000102/pdfft?md5=55bff66c4b20b15f29ecb5d4aca7346b&pid=1-s2.0-S0009281924000102-main.pdf","citationCount":"0","resultStr":"{\"title\":\"Mobilization of rare earth elements during extreme weathering of basalt\",\"authors\":\"Sinjan Roy , Shiba Shankar Acharya , Ramananda Chakrabarti\",\"doi\":\"10.1016/j.chemer.2024.126086\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>To investigate the mobility of elements during extreme weathering of basalts, major and trace elements concentrations along with the mineralogical abundance of weathered products, are reported for lateritic profiles developed over the ~118.1 ± 0.3 Ma old Rajmahal Trap basalts in Eastern India. Special emphasis has been given to studying the re-distribution of rare earth elements during extreme chemical weathering of relatively less explored Rajmahal flood basalt, which results in the development of lateritic profiles. Here, we conduct a systematic attempt to decipher the alteration of the composition of laterite developed over the Rajmahal flood basalt.</p><p>We demonstrate that the chemical index of alteration (CIA) and the mafic index of alteration (MIA) are less effective in deciphering extreme chemical weathering events, where desilication dominates the weathering process. In the weathered residues, the retention of REEs generally follows the trend of light rare earth elements (LREE) > middle rare earth elements (MREE) > heavy rare earth elements (HREE). Except for La and Ce, all other REEs show a depleting trend with reference to the parent rock composition. The ∑REE did not show any significant relationship with the commonly used weathering indices, which shows that the retention of REEs is not a function of the extent of weathering. The covariation of Ce anomaly with the Fe and Mn distribution in the samples reflects a redox-controlled mechanism. The negative correlation between the Eu anomaly and kaolinite abundance suggests that Eu mobilization from parent rock happens during initial weathering phases when plagioclase weathering dominates. The samples show an interesting positive Gd anomaly, which is explained by enhanced retention of Gd than neighboring Eu and Tb. During the chemical weathering of basalt, the retention of Ho was found to be greater than its geochemical twin Y. The results of this study show that significant differences exist between the REEs' distribution of parent basalt and that of the weathered residue, which has implications for the application of REEs as a provenance indicator and/or weathering proxy. 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引用次数: 0
摘要
为了研究玄武岩极端风化过程中元素的流动性,报告了在印度东部 ~118.1 ± 0.3 Ma 的拉杰马哈尔陷落玄武岩红土剖面上形成的主要元素和痕量元素浓度以及风化产物的矿物丰度。我们特别重视研究稀土元素在勘探相对较少的拉杰马哈尔洪积玄武岩极端化学风化过程中的重新分布,这导致了红土剖面的形成。我们证明,化学蚀变指数(CIA)和岩浆蚀变指数(MIA)在解密极端化学风化事件方面效果较差,在极端化学风化事件中,脱硅作用在风化过程中占主导地位。在风化残留物中,REEs 的保留一般遵循轻稀土元素 (LREE) > 中稀土元素 (MREE) > 重稀土元素 (HREE) 的趋势。除 La 和 Ce 外,所有其他稀土元素与母岩成分相比都呈衰减趋势。∑REE与常用的风化指数没有明显关系,这表明REE的保留与风化程度无关。铈异常与样品中铁和锰分布的协变关系反映了一种氧化还原控制机制。Eu 异常与高岭石丰度之间的负相关关系表明,在斜长石风化占主导地位的初始风化阶段,Eu 会从母岩中迁移出来。样品显示出有趣的正钆异常,这是因为钆的保留比邻近的 Eu 和 Tb 强。该研究结果表明,REEs 在母体玄武岩和风化残留物中的分布存在显著差异,这对应用 REEs 作为产地指示剂和/或风化替代物具有影响。风化样品中 Th 和 U 的富集可通过添加上部大陆地壳成分的风化尘来解释。
Mobilization of rare earth elements during extreme weathering of basalt
To investigate the mobility of elements during extreme weathering of basalts, major and trace elements concentrations along with the mineralogical abundance of weathered products, are reported for lateritic profiles developed over the ~118.1 ± 0.3 Ma old Rajmahal Trap basalts in Eastern India. Special emphasis has been given to studying the re-distribution of rare earth elements during extreme chemical weathering of relatively less explored Rajmahal flood basalt, which results in the development of lateritic profiles. Here, we conduct a systematic attempt to decipher the alteration of the composition of laterite developed over the Rajmahal flood basalt.
We demonstrate that the chemical index of alteration (CIA) and the mafic index of alteration (MIA) are less effective in deciphering extreme chemical weathering events, where desilication dominates the weathering process. In the weathered residues, the retention of REEs generally follows the trend of light rare earth elements (LREE) > middle rare earth elements (MREE) > heavy rare earth elements (HREE). Except for La and Ce, all other REEs show a depleting trend with reference to the parent rock composition. The ∑REE did not show any significant relationship with the commonly used weathering indices, which shows that the retention of REEs is not a function of the extent of weathering. The covariation of Ce anomaly with the Fe and Mn distribution in the samples reflects a redox-controlled mechanism. The negative correlation between the Eu anomaly and kaolinite abundance suggests that Eu mobilization from parent rock happens during initial weathering phases when plagioclase weathering dominates. The samples show an interesting positive Gd anomaly, which is explained by enhanced retention of Gd than neighboring Eu and Tb. During the chemical weathering of basalt, the retention of Ho was found to be greater than its geochemical twin Y. The results of this study show that significant differences exist between the REEs' distribution of parent basalt and that of the weathered residue, which has implications for the application of REEs as a provenance indicator and/or weathering proxy. The enrichment of Th and U in the weathered samples is explained through the addition of aeolian dust of upper continental crustal composition.
期刊介绍:
GEOCHEMISTRY was founded as Chemie der Erde 1914 in Jena, and, hence, is one of the oldest journals for geochemistry-related topics.
GEOCHEMISTRY (formerly Chemie der Erde / Geochemistry) publishes original research papers, short communications, reviews of selected topics, and high-class invited review articles addressed at broad geosciences audience. Publications dealing with interdisciplinary questions are particularly welcome. Young scientists are especially encouraged to submit their work. Contributions will be published exclusively in English. The journal, through very personalized consultation and its worldwide distribution, offers entry into the world of international scientific communication, and promotes interdisciplinary discussion on chemical problems in a broad spectrum of geosciences.
The following topics are covered by the expertise of the members of the editorial board (see below):
-cosmochemistry, meteoritics-
igneous, metamorphic, and sedimentary petrology-
volcanology-
low & high temperature geochemistry-
experimental - theoretical - field related studies-
mineralogy - crystallography-
environmental geosciences-
archaeometry