| 华北克拉通胶北地体多期高级变质事件:来自石榴斜长角闪岩与花岗质浅色体锆石U-Pb定年与稀土元素的新证据 |
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| 引用本文： | 刘平华,田忠华,文飞,周万蓬,王义龙.华北克拉通胶北地体多期高级变质事件:来自石榴斜长角闪岩与花岗质浅色体锆石U-Pb定年与稀土元素的新证据[J].地球科学,2020,45(9):3196-3216. |
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| 作者姓名： | 刘平华 田忠华 文飞 周万蓬 王义龙 |
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| 作者单位： | 1.中国地质科学院地质研究所, 北京 100037 |
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| 基金项目： | 国家自然科学基金项目41672191国家自然科学基金项目41972205中国地质调查局地质大调查项目DD20190003中国地质调查局地质大调查项目DD20160121 |
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| 摘 要： | 胶北是华北克拉通一个记录了多期高级变质事件的前寒武纪变质地体，确定其每期变质-深熔事件时代与性质对进一步认识胶北乃至华北克拉通早前寒武纪地质演化具有十分重要的科学意义.本文以栖霞石榴斜长角闪岩及其伴生的花岗质浅色体为研究对象，通过锆石内部矿物包体、CL图像、LA-ICP-MS U-Pb定年与稀土元素组成的综合研究，发现石榴斜长角闪岩（19LR53-1）中锆石可进一步划分为两类:第一类（新太古代晚期）锆石通常具有浑圆状晶形且相对弱的（灰黑色）的阴极发光效应，18个该类锆石微区记录了十分一致的207Pb/206Pb年龄，变化于2 540±58 Ma至2 439±54 Ma之间，相应的加权平均年龄为2 498±25 Ma，应代表石榴斜长角闪岩遭受新太古代晚期变质作用的时代；第二类锆石通常具有柱状晶形且相对强的（灰色-灰白色）的阴极发光效应，14个该类锆石微区记录了十分一致的207Pb/206Pb年龄，变化于1 906±54 Ma至1 821±60 Ma之间，相应的加权平均年龄为1 865±30 Ma，被解释为石榴斜长角闪岩遭受古元古代晚期退变质作用的时代.花岗质浅色脉体（19LR53-2）中绝大多数锆石具有不规则状晶形且相对弱的（灰黑色）阴极发光效应，有的含有少量长英质矿物包体，如钾长石+斜长石+石英+磷灰石，18个该类锆石微区记录的207Pb/206Pb年龄变化于2 521±48 Ma至2 453±42 Ma之间，相应的加权平均年龄为2 480±22 Ma，应代表胶北地体新太古代晚期地壳深熔作用的时代.综合本文与前人发表的同位素年代学资料可知，胶北地体太古宙变质基底岩石不仅经历了新太古代晚期~2 500 Ma高级变质作用与地壳深熔作用，而且还叠加了古元古代晚期~1 850 Ma的高级变质作用与地壳深熔作用，它们可能是华北克拉通两次克拉通化过程中的地质响应.
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| 关 键 词： | 胶北地体 多期高级变质事件 石榴斜长角闪岩 锆石U-Pb定年 岩石学 |
| 收稿时间： | 2020-07-17 |
Multiple High-Grade Metamorphic Events of the Jiaobei Terrane,North China Craton: New Evidences from Zircon U-Pb Ages and Trace Elements Compositions of Garnet Amphilbote and Granitic Leucosomes |
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| Abstract: | The Jiaobei is a typical Precambrian metamorphic terrane in the North China Craton that records multiple high-grade metamorphic events. It is of great scientific significance to determine the nature, timing of each metamorphic event in order to further understand the geological evolution of the early Precambrian in the Jiaobei Terrane and even the North China Craton. A combined study of mineral inclusions, cathodoluminescence (CL) images, LA-ICP-MS U-Pb dating, and in-situ rare earth element (REE) compositions of zircons provides clear evidence on the timing of the metamorphism and partial melting in the Qixia garnet amphibolites and related granitic leucosomes. The zircons separated from garnet amphibolites (19LR53-1) can be subdivided into two distinct zircon domains: The late Neoarchean zircons are rounded in shape and black-luminescent in CL images, eighteen late Neoarchean zircons record a consistent 207Pb/206Pb age, ranging from 2 540±58 Ma to 2 439±54 Ma with a weighted average age of 2 498±25 Ma, which represents the late Neoarchean metamorphic timing of the garnet amphibolites. In contrast, the late Paleoproterozoic zircons usually have columnar crystals and relatively high (grey-off-white) cathodoluminescence in CL image. Fourteen late Paleoproterozoic zircons record a consistent 207Pb/206Pb age, ranging from 1 906±54 Ma to 1 821±60 Ma with a weighted average age of 1 865±30 Ma, which represents the retrogressive timing of garnet amphibolites during late Paleoproterozoic cratonization. The zircons in the granitic leucosomes (19LR53-2) have irregular crystal shapes and relatively weak (gray-black) cathodoluminescence in the CL image. Some of them contain felsic mineral inclusions, such as K-feldspar+plagiclase+quartz+apatite. Eighteen zircons from the granitic leucosomes record a consistent 207Pb/206Pb age, ranging from 2 521±48 Ma to 2 453±42 Ma with a weighted average age of 2 480±22 Ma. The age is interpretated as the late Neoarchean anatectic timing of the Jiaobei terrane, which, together with the published data, suggests that the Archean basement rocks of the Jiaobei terrane have not only experienced the high-grade metamorphism and crustal anatexis in the late Neoarchean, but also overprinted the high-grade metamorphism and crustal anatexis in the late Paleoproterozoic. They may be the geological responses of the two cratonizations of the North China Craton. |
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