| 内蒙古孔兹岩带乌拉山-大青山地区古元古代孔兹岩系年代学研究 |
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| 引用本文： | 蔡佳,刘福来,刘平华,王舫,施建荣.内蒙古孔兹岩带乌拉山-大青山地区古元古代孔兹岩系年代学研究[J].岩石学报,2015,31(10):3081-3106. |
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| 作者姓名： | 蔡佳 刘福来 刘平华 王舫 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,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 |
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| 基金项目： | 本文受国家自然科学重点基金项目(41430210)、科技部973项目(2012CB416603)和中国地质调查局地质大调查项目(12120114061901、12120114021401)联合资助. |
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| 摘 要： | 乌拉山-大青山孔兹岩系岩石出露于华北克拉通孔兹岩带中段,是洞悉华北克拉通前寒武纪基底构造演化历史的一个重要窗口。研究区孔兹岩系岩石包括堇青石榴黑云二长片麻岩、夕线堇青石榴黑云二长片麻岩、紫苏石榴黑云片麻岩和石榴长英质粒状岩石,系统的岩相学观察显示多种典型的减压反应结构。阴极发光图像特征显示乌拉山-大青山孔兹岩系岩石均存在大量继承性碎屑锆石和变质增生锆石,其中继承性碎屑锆石形态复杂,多显示典型岩浆结晶环带,标志着源区物质主要来源于岩浆岩。变质锆石为新生的单颗粒或围绕着继承性碎屑锆石核生长,内部结构均匀,整体的Th/U比值较低。锆石LA-ICP-MS U-Pb定年结果表明,该区孔兹岩系岩石的继承性碎屑锆石的207Pb/206Pb年龄主要集中在2400~2500Ma、~2300Ma和2000~2100Ma,进而可限定其最老沉积时代应为~2000Ma,表明乌拉山-大青山孔兹岩系的原岩形成时代为古元古代中期。乌拉山-大青山孔兹岩系中典型的变质锆石记录其变质时代为1850~1950Ma,并显示~1950Ma和~1860Ma两组年龄峰。结合前人对内蒙古孔兹岩带乌拉山-大青山地区高级变质地体的变质作用、构造演化和同位素年代学的研究结果,综合判断该期变质事件与古元古代华北克拉通西部陆块内北部的阴山陆块和南部的鄂尔多斯陆块之间的俯冲-碰撞并折返抬升至地表的动力学过程有关,其中~1950Ma代表了陆-陆碰撞形成孔兹岩带的初始阶段,而~1860Ma则代表了其折返抬升的时代。
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| 关 键 词： | 孔兹岩系 古元古代 LA-ICP-MS U-Pb定年 乌拉山-大青山地区 孔兹岩带 |
| 收稿时间： | 3/1/2015 12:00:00 AM |
| 修稿时间： | 2015/5/26 0:00:00 |
Geochronology of the Paleoproterozoic khondalite rocks from the Wulashan-Daqingshan area, the Khondalite Belt |
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| CAI Ji,LIU FuLai,LIU PingHu,WANG Fang and SHI JianRong.Geochronology of the Paleoproterozoic khondalite rocks from the Wulashan-Daqingshan area, the Khondalite Belt[J].Acta Petrologica Sinica,2015,31(10):3081-3106. |
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| Authors: | CAI Ji LIU FuLai LIU PingHu WANG Fang 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,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China and Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | The khondalite rocks are cropped out in the Wulashan-Daqingshan area, central segment of the Khondalite Belt, which are important to illustrating the metamorphic and tectonic evolution of the Precambrian basement rocks. The studied khondalite rocks consist of cordierite-garnet-biotite gneiss, sillimanite-cordierite-garnet gneiss, hypersthene-garnet-biotite gneiss, and garret-bearing quartzofeldspathic rock, showing distinct decompressional textures after petrographic observations. Cathodoluminescent images show that zircons contained in the Wulashan-Daqingshan khondalite rocks mostly are detrital and metamorphic zircons. Detrital zircons reveal oscillatory zoning with igneous origin, and the metamorphic zircons occur either as single grains or overgrowth rims surrounding detrital zircon cores which are homogeneous and low in Th/U ratio. LA-ICP-MS U-Pb analyses on magmatic-type detrital zircons yield three distinct age populations of 2400~2500Ma, ~2300Ma and 2000~2100Ma, suggesting that the sedimentary protoliths of the khondalite rocks in the Wulashan-Daqingshan area have been deposited at some time after ~2000Ma. Analyses of LA-ICP-MS U-Pb dating for metamorphic zircons indicate that the metamorphic zircons of the khondalite rocks range in 1850~1950Ma yielding two age groups, with one at ~1950Ma and the other at ~1860Ma. These new zircon ages in combination with metamorphic and tectonic considerations, indicate that the Wulashan-Daqingshan Paleoproterozoic granulite-facies metamorphic event involving in the subduction and collision followed by post-collisional extension and subsequent exhumation between the Yinshan block to the north and the Ordos block to the south to form the Khondalite Belt in the Western Block of the North China Craton. Moreover, ~1950Ma is considered the timing of the collision between the Yinshan and the Ordos blocks to form the Western Block, whereas ~1860Ma should be the timing of exhumation stage. |
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| Keywords: | Khondalite rocks Paleoproterozoic LA-ICP-MS U-Pb dating Wulashan-Daqingshan area The Khodalite Belt |
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