华北克拉通南缘小秦岭地区浅色花岗质脉体锆石U-Pb年龄、稀土元素特征及其地质意义
投稿时间:2021-12-29  修订日期:2022-03-17  点此下载全文
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作者单位邮编
王宏晖 中国地质科学院地质力学研究所 100081
陈虹 中国地质科学院地质力学研究所 
陈龙耀 中国地质科学院地质力学研究所 
白和 陕西省地质矿产勘查开发局第六地质队 
张欢欢 陕西省地质矿产勘查开发局第六地质队 
基金项目:国家自然科学基金项目(编号41772217、41872225)和中国地质调查局地质调查项目(编号12120114014101)联合资助
中文摘要:华北克拉通南缘的小秦岭地区发育大量浅色花岗质脉体,这为深入理解古元古代时期克拉通构造演化提供了重要的窗口。本文对小秦岭地区三条浅色花岗质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。三件样品中的锆石具深熔/变质成因锆石的斑杂状、平面状或弱振荡环带的内部结构特征,测得的锆石207Pb/206Pb年龄分别为1867±13Ma (MSWD=0.22, n=21)、1849±17Ma (MSWD=0.79)和1828±15Ma (MSWD=0.33, n=20)。与三组年龄相对应,其稀土元素配分曲线由具显著-较弱负Eu异常 (Eu/Eu*=0.12~0.81)的重稀土相对富集型转变为具中等-明显负Eu异常 (Eu/Eu*=0.29~0.61)的平坦重稀土型、再到具显著负Eu异常 (Eu/Eu*=0.15~0.54)的重稀土富集型,表明它们形成于不同变质阶段的深熔作用。结合前人的变质年代学数据,本文认为小秦岭地区1.87~1.83 Ga的深熔作用与东、西部陆块持续碰撞造山过程中的板内调节事件有关。
中文关键词:华北克拉通南缘  古元古代  浅色花岗质脉体  LA-ICP-MS  锆石U-Pb定年  稀土元素
 
Zircon U-Pb Age and Rare Earth Element of Leucogranite Dykes from the Xiaoqinling Area in the Southern Margin of the North China Craton and Their Geological Implications
Abstract:A large number of leucogranite dykes are developed in the Xiaoqinling area of the southern North China Craton (NCC), which are of great significance for the Paleoproterozoic tectonic evolution of the Craton. In this paper, cathodoluminescence (CL) images, U-Pb chronology and rare earth elements (REE) of zircons from three leucogranite dykes in the Xiaoqinling area are studied. The CL images display patched, planar or weakly oscillatory zonings, which are typical for anatectic/metamorphic zircons. Zircon U-Pb dating yields 207Pb/206Pb ages of 1867±13Ma (MSWD=0.22, n=21), 1849±17Ma (MSWD=0.79) and 1828±15Ma (MSWD=0.33, n=20), respectively. 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 obvious to weak Eu anomalies (Eu/Eu*=0.12~0.81) to flat HREE patterns with medium to obvious negative Eu anomalies (Eu/Eu*=0.29~0.61), and then to the enrichment of HREEs with obvious negative Eu anomalies (Eu/Eu*=0.15~0.54), indicating they are formed by anatexis during different stages of metamorphism. Combined with the previous metamorphic chronological data, it is inferred that the anatexis during 1.87~1.83Ga in the Xiaoqinling area can be linked to a within-plate adjustment event in the protract collision between the Eastern and Western blocks.
keywords:Southern North China Craton  Paleoproterozoic  Leucogranite dykes  LA-ICP-MS  Zircon U-Pb dating  Rare earth element
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