| 稀有金属伟晶岩过度冷却与侵位之关系——基于野外地质观察及年代学的思考 |
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| 引用本文： | 凤永刚,梁婷,雷如雄,鞠明辉,张忠利,高景刚,周义,吴昌志.稀有金属伟晶岩过度冷却与侵位之关系——基于野外地质观察及年代学的思考[J].地球科学与环境学报,2021(1):100-116. |
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| 作者姓名： | 凤永刚 梁婷 雷如雄 鞠明辉 张忠利 高景刚 周义 吴昌志 |
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| 作者单位： | 长安大学地球科学与资源学院;长安大学成矿作用及其动力学实验室;新疆维吾尔自治区有色地质勘探局七〇六队 |
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| 基金项目： | 国家自然科学基金重大研究计划项目(9196220013);国家重点研发计划项目(2019YFC0605202)。 |
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| 摘 要： | 稀有金属伟晶岩的结晶过程是认识其成矿作用的重要方面。前人利用冷却模型所推测出的侵入变质围岩的伟晶岩冷却时间为几天至几千年,但对侵位于花岗岩中伟晶岩的结晶过程缺乏相关研究。基于此,对新疆大喀拉苏及镜儿泉地区稀有金属伟晶岩的野外地质观察及年代学研究显示,两处伟晶岩的侵位模式不同,侵位时花岗岩围岩的温度有别。大喀拉苏1号伟晶岩(年龄为(248.4±2.1)~(228.4±0.3)Ma)主要侵位于较冷花岗岩围岩(年龄为(261.4±2.1)Ma)的席理面,边缘可能出现过度冷却。最新铌钽铁矿U-Pb年代学显示,镜儿泉1号锂辉石伟晶岩形成时代为(250.8±1.0)Ma,熔体侵位于温度较高的花岗岩(年龄为(252.9±1.9)Ma)内部断层,其冷却结晶受花岗岩温度及区域地热梯度制约,冷却时间可能超过3 Ma。综上所述,过度冷却模型的适用性、铌钽铁矿U-Pb同位素体系的封闭温度都需要进一步研究,以解释同位素年龄与冷却模型所得结晶时间的显著差异。
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| 关 键 词： | 稀有金属伟晶岩 花岗岩 结晶过程 过度冷却 侵位模式 围岩 铌钽铁矿U-Pb年代学 新疆 |
Relationship Between Undercooling and Emplacement of Rare-element Pegmatites—Thinking Based on Field Observations and Pegmatite Geochronology |
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| FENG Yong-gang,LIANG Ting,LEI Ru-xiong,JU Ming-hui,ZHANG Zhong-li,GAO Jing-gang,ZHOU Yi,WU Chang-zhi.Relationship Between Undercooling and Emplacement of Rare-element Pegmatites—Thinking Based on Field Observations and Pegmatite Geochronology[J].Journal of Earth Sciences and Environment,2021(1):100-116. |
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| Authors: | FENG Yong-gang LIANG Ting LEI Ru-xiong JU Ming-hui ZHANG Zhong-li GAO Jing-gang ZHOU Yi WU Chang-zhi |
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| Institution: | (School of Earth Science and Resources,Chang an University,Xi an 710054,Shaanxi,China;Laboratory of Mineralization and Dynamics,Chang an University,Xi an 710054,Shaanxi,China;No.706 Geological Team,Xinjiang Nonferrous Geoexploration Bureau,Altay 836500,Xinjiang,China) |
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| Abstract: | Crystallization processes of rare-element pegmatites are one of the key aspects in understanding pegmatite-hosted mineralization.Based on the undercooling model proposed in previous studies,the cooling time for rare-element pegmatites intruded into metamorphic rocks was estimated to be several days to several thousand years.The model,however,has not fully addressed the cooling and crystallization of rare-element pegmatites hosted by granites.Field observations and geochronology of two representative rare-element pegmatites hosted by granites in Dakalasu and Jing erquan areas of Xinjiang illustrate that their emplacement models are different,and the granite wall rocks are at different temperatures during the moment of their emplacement.Dakalasu No.1 pegmatite(formed from(248.4±2.1)Ma to(228.4±0.3)Ma)is emplaced into the sheeting joints of a relatively cold host granite(formed at(261.4±2.1)Ma),and undercooling likely occurs in the marginal zone of the pegmatite.By contrast,the latest columbite U-Pb chronology shows that Jing erquan No.1 spodumene pegmatite(formed at(250.8±1.0)Ma)is intruded in a relatively hot granite(formed at(252.9±1.9)Ma)through a fault.The cooling and crystallization of the pegmatite in Jing erquan area is likely controlled by the temperature of the granite and the regional geothermal gradient,indicating a cooling history over 3 Ma.Therefore,the undercooling model and the closure temperature for the columbite U-Pb isotopic systematics need further investigation to solve the discrepancies between isotopic ages and the cooling time based on the modeling. |
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| Keywords: | rare-metal pegmatite granite crystallization process undercooling emplacement model wall rock columbite U-Pb geochronology Xinjiang |
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