华北地块北缘上石炭统—中三叠统碎屑锆石研究及其地质意义  

A study of detrital zircons of Late Carboniferous-Middle Triassic strata in the northern margin of North China block and its geological implication

作　　者：马收先[1,2] 孟庆任[1] 曲永强[3] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]中国科学院研究生院地球科学学院,北京100039 [3]中国石油勘探开发研究院西北分院,甘肃兰州730020

出　　处：《地质通报》2011年第10期1485-1500,共16页Geological Bulletin of China

基　　金：国家自然科学基金面上项目<燕山构造带中部晚侏罗世火山沉积演化及构造意义>(批准号:40972151);中国科学院知识创新工程重要方向项目<外贝加尔-华北断面(南段):地质构造格局及成矿背景>(编号:KZCX2-YW-Q04-04)

摘　　要：利用碎屑锆石U-Pb年龄和Hf同位素对平泉地区晚石炭世—中三叠世地层进行物源分析,重塑内蒙古隆起的隆升历史,进而探讨古亚洲洋的闭合过程。5个样品的LA-ICP-MS碎屑锆石U-Pb年龄由5个年龄峰组成:峰1中晚二叠世(270~250Ma)、峰2晚石炭世—早二叠世(325~290Ma)、峰3泥盆纪(400~360Ma)、峰4古元古代(1900~1700Ma)和峰5新太古代-古元古代早期(2600~2400Ma)。其中,本溪组碎屑锆石主要由峰3、峰4和峰5组成,山西组、孙家沟组和刘家沟组则主要由峰2和峰4组成,下石盒子组由峰1、峰4和峰5组成。5个样品具有相同的Hf同位素特征,显生宙锆石的εHf(T)在-3.2^-25.5之间,与内蒙古隆起的晚古生代侵入岩体完全相同。碎屑锆石U-Pb年龄和Hf同位素特征显示物源主要来自内蒙古隆起,不同层位的物源变化表明内蒙古隆起曾存在2次重要的隆升事件:第一期发生在360~312Ma之间,第二期发生在276~258Ma期间。第一次隆升奠定了盆-山的基本构造格局,第二次隆升之后古隆起进入稳定剥蚀期,为盆地提供持续稳定的物源,盆地内部发育了一套粗碎屑沉积物,可以推断在276Ma左右古亚洲洋已经关闭。In order to interpret the uplift history of Inner Mongolia Paleo-uplift and understand the tectonic evolution of Paleo-Asian Ocean,the authors conducted U-Pb dating and Hf isotope analysis of detrital zircons from distinct levels of Late Carboniferous-Middle Triassic strata in Pingquan.U-Pb ages of detrital zircons from five samples fall into five groups,i.e.,Group 1 of Middle-Late Permian（270~250Ma）,Group 2 of Late Carboniferous-Early Permian（325~290Ma）,Group 3 of Devonian（400~360Ma）,Group 4 of Paleoproterozoic（1900~1700Ma） and Group 5 of Neoarchean-Paleoproterozoic（2600~2400Ma）.Among these five samples,age spectra of Benxi Formation are composed of Group 3,Group 4 and Group 5,age spectra of Shanxi Formation,Sunjiagou Formation and Liujiagou Formation mainly consist of Group 2 and Group 4,and age spectra of Lower Shihezi Formation are composed of Group 1,Group 4 and Group 5.In addition,zircons from the five samples have the same Hf isotope characteristics.εHf（T） values of Phanerozoic zircons range from-3.2 to-25.5,consistent with the values of Late Paleozoic plutons in Inner Mongolia Paleo-uplift.The zircon age constituents and Hf isotopes suggest a provenance from Inner Mongolia Paleo-uplift,and the zircon age variation through different levels implies two critical uplifting events,which occurred during 360~312Ma and 276~258Ma respectively.360~312Ma uplift built up the tectonic framework of the North China basin and provided sediments for the basin.After 276~258Ma uplift event,Inner Mongolia Paleo-uplift was steadily denuded and thus supplied a great amount of coarse-grained sediments to the sedimentary basin which had unchanged U-Pb age spectra of detrital zircons,suggesting that the Paleo-Asian Ocean might have been closed before 276Ma.

关 键 词：古亚洲洋 华北地块北缘 晚石炭世—中三叠世 LA-ICP-MS碎屑锆石U-Pb年龄 

分 类 号：P597.3[天文地球—地球化学]