New insight into biotite weathering in the subtropic Tongcheng granite regolith, Hubei Province, South China
New insight into biotite weathering in the subtropic Tongcheng granite regolith, Hubei Province, South China
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DOI：
10.1016/j.clay.2022.106518
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发表时间：
2022-07
影响因子：
5.6
通讯作者：
Shih-Cheang Cheng;H. Hong;Kaipeng Ji;Fan Li;Xinghong Wang
中科院分区：
文献类型：
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作者：
Shih-Cheang Cheng;H. Hong;Kaipeng Ji;Fan Li;Xinghong Wang
火成岩风化过程中黑云母的蚀变作用对全球地球化学循环和离子吸附型稀土矿的形成起着重要作用。为了更好地了解黑云母风化作用的转化和地球化学过程，对亚热带湖北桐城花岗岩风化层中的黑云母进行了蚀变研究。结果表明，黑云母的风化作用同时产生了黑云母/蛭石（B/V）和埃洛石的随机间层，B/V粘土由于风化作用的增强而部分分解为离散的蛭石。黑云母的蠕滑化过程是由K+的淋溶和Mg 2+、Fe 3+的水化在黑云母先驱体层间的聚集而发生的固-固转变。B/V相中的蛭石组分为羟基层间物种，新形成的埃洛石不能被甲酰胺处理膨胀，指示脱水埃洛石。埃洛石以管状形态出现在黑云母的边缘，或以定向良好的板条状团簇出现在黑云母晶体的基底表面。前者从溶液中结晶，而后者形成的Sisingle bondO片的黑云母，随后在原位重结晶的局部浸出。由于黑云母前驱体晶体结构中四面体和八面体的尺寸失配，在一定的方向上形成了平行的板条状埃洛石团簇，其角度分别为~30°和~ 60°。因此，埃洛石的形成可以被认为是一个溶解-沉淀过程。
Alteration of biotite during igneous rock weathering plays an important role in global geochemical cycle and formation of ion-adsorption type rare earth element ores. In order to better understanding the transformation and geochemical processes of biotite weathering, investigation of alteration of biotite was undertaken in the granite regolith in subtropical Tongcheng, Hubei Province, South China. Our results show that weathering of biotite synchronously produced randomly interstratified biotite/vermiculite (B/V) and halloysite, and the B/V clay partially decomposed into discrete vermiculite in the topsoil due to increasing weathering. Vermiculitization of biotite involved leaching of K+and accumulation of hydrated Mg2+and Fe3+in the interlayer space of biotite precursor and thus occurred in a solid-solid state transformation. The vermiculite components in B/V phase are hydroxyl-interlayered species, and the neoformed halloysite could not be expanded by formamide treatment, indicative of dehydrated halloysite. Halloysite occurs in tubular morphology at the edge of biotite or in well-oriented lath-like clusters on the basal surface of biotite crystals. The former crystallized from solutions, whereas the latter formed from local leaching of Sisingle bondO sheets of biotite and subsequently in situ recrystallization. The parallel lath-like halloysite clusters occur in certain extending directions with angles of ~30° and ~ 60° respectively, resulting from the size misfit between the tetrahedron and octahedron of the crystal structure of biotite precursor. Thus, the formation of halloysite can be considered as a dissolution–precipitation process.