| 冀西北怀安地体高级变质表壳岩的锆石年代学研究 |
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| 引用本文： | 蔡佳,刘平华,冀磊,施建荣.冀西北怀安地体高级变质表壳岩的锆石年代学研究[J].岩石学报,2017,33(9):2811-2826. |
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| 作者姓名： | 蔡佳 刘平华 冀磊 施建荣 |
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| 作者单位： | 中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,天津地质矿产研究所, 天津 300170 |
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| 基金项目： | 本文受国家自然科学基金项目（41430210、41502181）、中国地质调查局地质大调查项目（DD20160121）和中国地质科学地质研究所基本科研业务费（YYWF201703、J1713）联合资助. |
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| 摘 要： | 位于华北克拉通中部造山带中北段的怀安地体与内蒙孔兹岩带相接,出露高压麻粒岩和退变榴辉岩等多种高级变质岩,是洞悉华北克拉通古元古代构造演化历史的重要窗口。研究区变质表壳岩包括夕线石榴长英质片麻岩、石榴长英质粒状岩石以及紫苏黑云二长片麻岩。阴极发光图像特征显示研究区样品的锆石主要包括碎屑锆石和变质锆石,其中碎屑锆石具有岩浆结晶环带,而变质锆石为单颗粒或围绕着继承性碎屑锆石边部生长,内部结构均匀,Th/U比值较低。锆石LAICP-MS U-Pb定年结果与前人研究结果综合表明该区变质表壳岩石的碎屑锆石的207Pb/206Pb年龄主要集中在~2040Ma,其原岩形成时代与孔兹岩带变泥质岩石相近,均为~2.0Ga。变质锆石记录其变质时代为1957~1804Ma,结合前人对怀安地区变泥质岩和变基性岩变质作用和年代学研究结果,推测得出1.95~1.92Ga代表了峰期(高压)麻粒岩相变质时代,1.90~1.85Ga代表峰后减压阶段变质时代,而1.85~1.80Ga代表退变质晚期的时代。怀安地区变质岩石可能卷入了阴山陆块、鄂尔多斯陆块以及东部陆块间的先后碰撞造山过程,并持续较长时间(1.95~1.80Ga),最终拼贴为统一的整体。
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| 关 键 词： | 变质表壳岩 古元古代 LA-ICP-MS U-Pb定年 怀安地体 中部造山带 |
| 收稿时间： | 2017/2/23 0:00:00 |
| 修稿时间： | 2017/5/30 0:00:00 |
Zircon geochronology of the Paleoproterozoic high-grade supracrustal rocks from the Huai'an terrane, northwestern Hebei |
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| CAI Ji,LIU PingHu,JI Lei and SHI JianRong.Zircon geochronology of the Paleoproterozoic high-grade supracrustal rocks from the Huai'an terrane, northwestern Hebei[J].Acta Petrologica Sinica,2017,33(9):2811-2826. |
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| Authors: | CAI Ji LIU PingHu JI Lei and SHI JianRong |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China and Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China |
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| Abstract: | The Huai''an terrane with the occurrences of high-grade metamorphic rocks including high-pressure granulites and retrograded eclogites is located in the north-central segment of the Trans-North China Orogen adjacent to the Khondalite Belt in North China Craton, which is particularly important to investigating its Paleoproterozoic crustal evolution history. The studied supracrustal rocks consist of sillimanite-garnet gneiss, garnet-bearing quartzofeldspathic rock, and orthopyroxene-bearing quartzofeldspathic gneiss. Cathodoluminescent images show that zircons in the studied Huai''an metamorphic rocks are predominantly detrital and metamorphic zircons. Detrital zircons with oscillatory zoning have igneous origin, and metamorphic zircons occur either as single grains or overgrowth rimming detrital zircon cores which are homogeneous with relatively low Th/U ratio. LA-ICP-MS U-Pb analyses on magmatic-type detrital zircons combined with other published zircon dating results yielded a concentrated 207Pb/206Pb age population of~2040Ma, indicating that the sedimentary protolith age of the Huai''an supracrustal rocks is~2.0Ga, which is similar to other metapelitic rocks within the Khondalite Belt. Based on previous published results of U-Pb dating and P-T evolution in the Huai''an metapelitic and metabasic rocks, metamorphic ages of 1957~1804Ma for the studied samples is presumed to be subdivided into three age groups at 1.95~1.92Ga, 1.90~1.85Ga, and 1.85~1.80Ga representing peak (high-pressure) granulite-facies metamorphic stage, post-peak decompressional stage, and late cooling stage. These new zircon ages in combination with metamorphic and tectonic considerations indicate that basement rocks of the Huai''an terrane might involved in the continuous subduction and collision followed by post-collisional extension and subsequent exhumation processes of the Yinshan, Ordos, and Eastern blocks during 1.95~1.80Ga and eventually amalgamated as a uniform basement. |
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| Keywords: | Supracrustal rocks Paleoproterozoic LA-ICP-MS U-Pb dating Huai''an terrane The Trans-North China Orogen |
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