| 王三达.大别造山带石关地区变质岩风化壳中REY富集和分异研究[J].地质与勘探,2023,59(4):828-851 |
| 大别造山带石关地区变质岩风化壳中REY富集和分异研究 |
| Enrichment and fractionation of REY in the weathering crust of metamorphic rocks in the Shiguan area of the Dabie orogenic belt |
| 投稿时间：2023-01-28 修订日期：2023-06-27 |
| DOI：10.12134/j.dzykt.2023.04.011 |
| 中文关键词: 变质岩风化壳 风化壳矿物 REY赋存状态 REY分异 石关地区 大别造山带 |
| 英文关键词: weathering crust of metamorphic rock, weathering crust mineral, REY occurrence state, REY differentiation, Shiguan area, Dabie orogenic belt |
| 基金项目:国家自然科学基金面上项目（编号：42072089）资助 |
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| 中文摘要: |
| 最新的找矿勘查在大别造山带变质岩风化壳中发现稀土元素（REY、REEs+Y）的富集，为揭示高纬度地区变质岩风化壳中REY风化富集规律提供了契机。本文以大别山地区石关变质岩风化壳剖面作为研究对象，通过岩相学、地球化学、XRD、V-SWIR、顺序提取实验等分析，探讨原生矿物-次生矿物转变、REY来源、迁移富集规律及分异机制。研究认为：石关风化壳的基岩为石英二长片麻岩，稀土元素总量（∑REY）范围为280×10-6~310×10-6，呈LREE相对富集的右倾式稀土配分型式，角闪石（∑REY=722×10-6~795×10-6）和榍石（∑REY=12635×10-6~13351×10-6）是基岩中主要的REY载体，也是风化壳内REY的主要来源，风化壳整体的稀土元素配分继承于基岩。风化壳剖面由下至上REY含量逐渐增高（∑REY=469×10-6~535×10-6），对应的矿物组成上长石类矿物减少、石英和次生矿物（黏土矿物、铁锰氧化物等）增多，其中黏土矿物中伊利石含量逐渐减少，绿泥石、高岭石含量逐渐增多。顺序提取实验表明残余态是风化壳中REY的主要赋存状态（占比69％~88％），越靠近风化壳上部，可被提取出的、活化的REY占比越高，活化的REY以离子交换、铁锰氧化物结合和有机质结合等方式被固定在风化壳中。(La/Yb)N指示离子吸附态、有机质结合态和铁锰氧化物态均显示HREY相对富集的稀土分异趋势。 |
| 英文摘要: |
| Latest prospecting and exploration of the Dabie orogenic belt have found enrichment of rare earth elements (REY, REEs+Y) in weathering crust profiles of metamorphic rocks, providing an opportunity to reveal the enrichment mechanism of REY in the weathering crust profiles of metamorphic rocks at high latitudes. Taking a weathering crust profile of Shiguan metamorphic rock in Dabie orogenic belt as the research object, this work conducted petrography, geochemistry, XRD, V-SWIR and sequential extraction experiments, and discussed the transformation of primary and secondary minerals, REY source, migration and enrichment laws and differentiation mechanisms. This research shows that the bedrock of the Shiguan weathering crust is quartz monzonitic gneiss, with a total REY content (∑REY) ranging from 280×10-6 to 310×10-6, showing a right-inclined REY distribution pattern with relatively enriched LREE. Hornblende (∑REY=722×10-6~795×10-6) and titanite (∑REY=12635×10-6~13351×10-6) are the main REY carriers in the bedrock and the main source of REY in the weathering crust. The overall REY pattern of the weathering crust is mainly inherited from the bedrock. The weathering crust profile gradually increases in REY content from bottom to top (∑REY=469×10-6~535×10-6), accompanied by a decrease in feldspar minerals and an increase in quartz and secondary minerals (clay minerals, iron-manganese oxides, etc.), in which the content of illite in clay mineral gradually decreases, while the contents of chlorite and kaolinite increase gradually. The sequential extraction experiment shows that the REY in the weathering crust mainly is hosted as a residual state (accounting for 69%~88%). The closer it is to the upper part of the weathered crust, the higher the proportion of extractable and activated REY is. The activated REY is fixed in the weathered crust through ion exchange, iron manganese oxide binding, and organic matter binding. (La/Yb)N ratios indicate that the ion adsorption state, organic matter bound state and iron-manganese oxide state all show the differentiation of REY with relative enrichment of HREY. |
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