The effect of fluid-aided modification on the Sm-Nd and Th-Pb geochronology of monazite and bastnasite: Implication for resolving complex isotopic age data in REE ore systems
文献类型：期刊论文
| 作者 | Li, Xiao-Chun3,4,5; Yang, Kui-Feng3,4,5; Spandler, Carl2; Fan, Hong-Rui3,4,5; Zhou, Mei-Fu1; Hao, Jia-Long3; Yang, Yue-Heng3 |
| 刊名 | GEOCHIMICA ET COSMOCHIMICA ACTA
 |
| 出版日期 | 2021-05-01 |
| 卷号 | 300页码:1-24 |
| 关键词 | Monazite Bastnasite Sm-Nd isotopes Th-Pb isotopes Hydrothermal alteration Byan Obo |
| ISSN号 | 0016-7037 |
| DOI | 10.1016/j.gca.2021.02.028 |
| 英文摘要 | Isotopic dating studies have revealed that many carbonatite-related REE ore systems have protracted and complex temporal evolution histories. The mechanisms that cause these complex dating results remain poorly understood. Here, we present an in-situ Sm-Nd and Th-Pb isotopic investigation of monazite and bastnasite from a geologically-complicated deposit, the world-class Bayan Obo REE deposit of China, with the aim of defining the general mechanisms accounting for the protracted age spread observed in this and many other REE deposits. Monazite and bastnasite are two principle REE ore minerals in the Bayan Obo deposit. Most of the studied monazite and bastnasite grains have experienced fluid-aided modification. The modified grains have generally homogeneous Sm and Nd contents and Sm-Nd isotopic compositions, implying low mobility of Sm and Nd during the modification process. Thus, the Sm-Nd chronometer can be used to constrain the primary crystallization timing of the REE minerals at 1293 +/- 48 Ma. However, altered REE minerals have apparent Pb-208-Th-232 ages (1248-261 Ma) that are variably younger than the primary crystallization age. In most samples, Th contents have no correlations with Pb-208-Th-232 ages, while Pb contents tend to decrease along with the younging trend of Pb-208-Th-232 ages. NanoSIMS mapping shows that Pb-208 and Pb-208/Th-232 are heterogeneous, and irregularly distributed in the altered grains. Such results are indicative of variable Pb loss during the fluid-aided modification process. Thus, many Th-Pb ages represent partial isotopic resetting and, hence, are geologically meaningless. Completely reset ages cluster at 450-400 Ma or 280-260 Ma, representing two discrete episodes of post-ore hydrothermal activity. Small amounts of monazite and bastnasite that were newly crystallized during these two overprinting episodes have initial Nd isotopic signatures approaching the time-evolved isotopic compositions of primary ores, which suggests insignificant REE input to the primary ores during these events. This study provides critical evidence to resolve complex dating results and disparate ore genesis models for the giant Bayan Obo deposit. Moreover, our results indicate the resistance of Sm-Nd isotopes, but the susceptibility of Th-(U)-Pb isotopes, to fluid-aided modification. Therefore, younger Th-U-Pb dates in geologically-complicated deposits should be treated with caution as they may represent partial resetting results and/or may not represent events of increased metal tenor. (C) 2021 Elsevier Ltd. All rights reserved. |
| 资助项目 | National Natural Science Foundation of China (NSFC)[42072092] ; National Natural Science Foundation of China (NSFC)[41930430] ; Key Research Program of the Innovation Academy for Earth Science, CAS[IGGCAS-201901] |
| WOS研究方向 | Geochemistry & Geophysics |
| 语种 | 英语 |
| WOS记录号 | WOS:000639154500001 |
| 出版者 | PERGAMON-ELSEVIER SCIENCE LTD |
| 资助机构 | National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; National Natural Science Foundation of China (NSFC) ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS ; Key Research Program of the Innovation Academy for Earth Science, CAS |
| 源URL | [http://ir.iggcas.ac.cn/handle/132A11/101145]  |
| 专题 | 地质与地球物理研究所_中国科学院矿产资源研究重点实验室 |
| 通讯作者 | Li, Xiao-Chun |
| 作者单位 | 1.Univ Hong Kong, Dept Earth Sci, Hong Kong, Peoples R China 2.Univ Adelaide, Dept Earth Sci, Adelaide, SA 5005, Australia 3.Chinese Acad Sci, Innovat Acad Earth Sci, Beijing 100029, Peoples R China 4.Univ Chinese Acad Sci, Coll Earth & Planetary Sci, Beijing 100049, Peoples R China 5.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Mineral Resources, Beijing 100029, Peoples R China |
| 推荐引用方式 GB/T 7714 | Li, Xiao-Chun,Yang, Kui-Feng,Spandler, Carl,et al. The effect of fluid-aided modification on the Sm-Nd and Th-Pb geochronology of monazite and bastnasite: Implication for resolving complex isotopic age data in REE ore systems[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2021,300:1-24. |
| APA | Li, Xiao-Chun.,Yang, Kui-Feng.,Spandler, Carl.,Fan, Hong-Rui.,Zhou, Mei-Fu.,...&Yang, Yue-Heng.(2021).The effect of fluid-aided modification on the Sm-Nd and Th-Pb geochronology of monazite and bastnasite: Implication for resolving complex isotopic age data in REE ore systems.GEOCHIMICA ET COSMOCHIMICA ACTA,300,1-24. |
| MLA | Li, Xiao-Chun,et al."The effect of fluid-aided modification on the Sm-Nd and Th-Pb geochronology of monazite and bastnasite: Implication for resolving complex isotopic age data in REE ore systems".GEOCHIMICA ET COSMOCHIMICA ACTA 300(2021):1-24. |
入库方式： OAI收割
来源：地质与地球物理研究所
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