First identification of baddeleyite related/linked to contact metamorphism from carbonatites in the world's largest REE deposit, Bayan Obo in North China Craton
First identification of baddeleyite related/linked to contact metamorphism from carbonatites in the world's largest REE deposit, Bayan Obo in North China Craton
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首次在世界最大的稀土矿床华北克拉通白云鄂博中鉴定出与碳酸盐岩接触变质作用有关的斜锆石
DOI：
10.1016/j.lithos.2017.05.015
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发表时间：
2017-07
期刊：
影响因子：
3.5
通讯作者：
Chen Zhen-Yu
中科院分区：
文献类型：
--
作者：
Zhang Shuan-Hong;Zhao Yue;Li Qiu-Li;Hu Zhao-Chu;Chen Zhen-Yu
斜锆石被认为是确定二氧化硅不饱和火成岩结晶年龄的关键矿物。在此，我们报告了在华北克拉通（中国）世界最大的稀土矿床白云鄂博富含稀土元素-铌-钍的碳酸岩中发现的斜斜锆石的新产状。对三个斜锆石样品进行 U-Th-Pb 测年得出结晶年龄为 310–270 Ma，最佳估计结晶年龄约为 280 Ma。这些年龄明显比 theca.1300 Ma Bayan Obo 碳酸盐岩年轻，但与附近侵入碳酸盐岩的二叠纪花岗岩大致同时期。因此，白云鄂博斜锆石并不是从导致白云鄂博碳酸岩和相关稀土铌钍矿床形成的碳酸岩浆中结晶出来的。相反，它是在与二叠纪花岗岩类就位有关的接触变质作用期间从热液和/或涉及锆石和白云石的反应中结晶出来的。这与电子显微探针分析结果一致，显示斜锆石中含有腐铝石包裹体，因为腐铝石是一种典型的镁质夕卡岩矿物，并且出现在碳酸盐岩和花岗岩之间的侵入接触面附近。我们的结果表明斜锆石可用于热液和接触变质过程的测年。
Baddeleyite has been recognized as a key mineral to determine the crystallization age of silica-undersaturated igneous rocks. Here we report a new occurrence of baddeleyite identified from REE-Nb-Th-rich carbonatite in the world's largest REE deposit, Bayan Obo, in the North China Craton (China). U-Th-Pb dating of three baddeleyite samples yields crystallization ages of 310–270 Ma with the best estimated crystallization age ofca.280 Ma. These ages are significantly younger than theca.1300 Ma Bayan Obo carbonatites, but broadly coeval to nearby Permian granitoids intruding into the carbonatites. Hence, the Bayan Obo baddeleyite did not crystallize from the carbonatitic magma that led to the formation of the Bayan Obo carbonatites and related REE-Nb-Th deposit. Instead, it crystallized from hydrothermal fluids and/or a reaction involving zircon and dolomite during contact metamorphism related to the Permian granitoid emplacement. This is in agreement with the results of electron microprobe analysis that show humite inclusions in baddeleyite, since humite is a typical magnesian skarn mineral and occurs in close proximity to the intrusive contacts between carbonatites and granitoids. Our results show that baddeleyite can be used for dating hydrothermal and contact metamorphic processes.
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