| 华北克拉通南缘小秦岭地区花岗质浅色脉体锆石U-Pb年龄、稀土元素特征及其地质意义 |
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| 引用本文：王宏晖,陈虹,陈龙耀,白和,张欢欢.2022.华北克拉通南缘小秦岭地区花岗质浅色脉体锆石U-Pb年龄、稀土元素特征及其地质意义[J].地球学报,43(5):633-644. |
| DOI：10.3975/cagsb.2022.041102 |
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| 基金项目:国家自然科学基金项目(编号: 41772217; 41872225);中国地质调查局地质调查项目(编号: 12120114014101) |
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| 中文摘要:小秦岭地区发育有大量古元古代晚期的花岗质浅色脉体, 这为理解同时期华北克拉通南缘的深熔作用和构造演化提供了重要的窗口。本文对小秦岭地区三条花岗质浅色脉体中的锆石开展了CL图像、LA-ICP-MS U-Pb年代学及稀土元素的研究。浅色脉体中的锆石具有深熔成因锆石的斑杂状、平面状或弱振荡环带的内部结构及较为自形的外部形态特征, 测得的锆石207Pb/206Pb年龄分别为(1867±13) Ma (MSWD=0.22, n=21)、(1849±17) Ma (MSWD=0.79)和(1828±15) Ma (MSWD=0.33, n=20), 代表了该区深熔作用发生的时间。与上述三组年龄相对应, 其锆石稀土元素配分曲线由具较弱负Eu异常(Eu/Eu*=0.12~0.81)的重稀土相对富集型, 转变为中等负Eu异常(Eu/Eu*=0.29~0.61)的近平坦重稀土型、再到显著负Eu异常(Eu/Eu*=0.15~0.54)的重稀土富集型, 结合锆石Ti温度计获取其结晶温度为574~708 °C, 表明地壳深熔作用的发生可能与高角闪岩相-麻粒岩相的退变质作用有关。结合前人的变质年代学数据可知, 小秦岭地区1.87~1.82 Ga的深熔作用应与~1.95 Ga时东、西部陆块碰撞造山所致增厚地壳的长期抬升和冷却过程有关。 |
| 中文关键词:华北克拉通南缘 古元古代 花岗质浅色脉体 深熔作用 锆石U-Pb定年 稀土元素 |
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| Zircon U-Pb Ages and Trace Element Compositions of Granitic Leucosomes from the Xiaoqinling Area in the Southern Margin of the North China Craton and Its Geological Implications |
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| Abstract:Numerous granitic leucosomes formed during the Late Paleoproterozoic are developed in the Xiaoqinling area of the southern North China Craton (NCC), providing an important window for understanding the crustal melting and tectonic evolution of the southern NCC during this period. In this study, cathodoluminescence (CL) images, U-Pb chronology and rare earth elements (REE) of zircons from three granitic leucosomes in the Xiaoqinling area are studied. The CL images exhibit patched, planar or weakly oscillatory zonings with euhedral external morphologies, which are typical for anatectic zircons. Zircon U-Pb dating yields 207Pb/206Pb ages of (1867±13) Ma (MSWD=0.22, n=21), (1849±17) Ma (MSWD=0.79) and (1828±15) Ma (MSWD=0.33, n=20), representing the timing of partial melting in this area. Corresponding to the three groups ages, the zircon chondrite normalized REE diagrams show the transition from the relative enrichment of heavy rare earth elements (HREEs) with weak Eu anomalies (Eu/Eu*=0.12–0.81) to nearly flat HREE patterns with medium negative Eu anomalies (Eu/Eu*=0.29–0.61), and then to an enrichment of HREEs with obvious negative Eu anomalies (Eu/Eu*=0.15–0.54), titanium-in-zircon temperature suggests that the crystallization temperatures are between 574 °C and 708 °C, implying that crustal anatexis occurred during the post-peak upper amphibolite-facies to granulite-facies stages. Combined with previous metamorphic chronological data, it is inferred that the anatexis occurred during 1.87~1.82 Ga in the Xiaoqinling area can be linked to the protracted uplift and cooling process of the previously thickened crust caused by the collision and amalgamation of the Eastern and Western Blocks at ~1.95 Ga. |
| keywords:southern North China Craton Paleoproterozoic granitic leucosomes anatexis zircon U-Pb dating rare earth element |
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