| 华北克拉通南缘五佛山群沉积时代和物源区分析:碎屑锆石U-Pb年龄和Hf同位素证据 |
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| 引用本文： | 胡国辉,赵太平,周艳艳,杨阳.华北克拉通南缘五佛山群沉积时代和物源区分析:碎屑锆石U-Pb年龄和Hf同位素证据[J].地球化学,2012(4):326-342. |
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| 作者姓名： | 胡国辉 赵太平 周艳艳 杨阳 |
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| 作者单位： | [1]中国科学院广州地球化学研究所,广东广州510640 [2]中国科学院研究生院,北京100049 [3]西北大学大陆动力学国家重点实验室,陕西西安710069 |
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| 基金项目： | 国家基础研究发展计划（2012CB416606）;西北大学大陆动力学国家重点实验室科技部专项经费 |
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| 摘 要： | 河南嵩山地区位于华北克拉通南缘,其早前寒武纪结晶基底主要由新太古代登封群表壳岩、TTG质片麻岩和古元古代嵩山群石英岩,以及新太古代-古元古代的花岗质岩石组成。五佛山群角度不整合覆盖于登封群和嵩山群之上,主要由石英砂岩组成,夹少量的粉砂质页岩和薄层灰岩,为该地区太古宙-古元古代结晶基底之上分布广泛的第一沉积盖层。探讨其沉积时代和物质来源,对揭示华北克拉通南缘前寒武纪地壳演化过程具有重要意义,并可为华北南缘前寒武纪地层框架的建立和对比提供依据。本文对五佛山群底部马鞍山组两个石英砂岩样品的碎屑锆石进行LA-ICP-MS U-Pb年龄测定,获得最年轻的207Pb/206Pb年龄分别为(1732±11)Ma和(1655±22)Ma,说明五佛山群形成时代的下限为古元古代晚期,与华北克拉通南缘熊耳群火山-沉积岩系之后的其他沉积盖层年代相当。五佛山群碎屑锆石207Pb/206Pb年龄范围为2816~1655 Ma,主要集中于2100~1800 Ma之间(约占60%),年龄主峰值为(1.93±0.10)Ga,部分年龄分布于2500~2100 Ma之间(约占24%),说明其沉积物质主要来源于古元古代的地质体,相比华北克拉通其他地区同时代的沉积地层碎屑锆石年代学研究结果,本区来自太古宙的物源极少。五佛山群马鞍山组碎屑锆石的U-Pb年龄反映了嵩山地区在1.93 Ga左右发生过重要的构造-热事件,与华北克拉通古元古代中期发生的变质作用时间(约1.91 Ga)一致。碎屑锆石εHf(t)值为–14.3~4.6,Hf的两阶段模式年龄分布于2363~3672 Ma之间,明显大于其207Pb/206Pb年龄,大部分锆石的Hf同位素组成集中于2.50 Ga和2.80 Ga地壳演化线区域内,揭示了新太古代为华北克拉通南缘重要的陆壳生长期。
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| 关 键 词： | 五佛山群 碎屑锆石 U-Pb年龄 源区 华北克拉通 |
Depositional age and provenance of the Wufoshan Group in the southern margin of the North China Craton： Evidence from detrital zircon U-Pb ages and Hf isotopic compositions |
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| HU Guo-hui,ZHAO Tai-ping,＊,ZHOU Yan-yan,and YANG Yang.Depositional age and provenance of the Wufoshan Group in the southern margin of the North China Craton： Evidence from detrital zircon U-Pb ages and Hf isotopic compositions[J].Geochimica,2012(4):326-342. |
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| Authors: | HU Guo-hui ZHAO Tai-ping ＊ ZHOU Yan-yan and YANG Yang |
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| Institution: | 1,21. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China;3. State Key Laboratory of Continental Dynamics, Northwest University, Xi＇an 710069, China |
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| Abstract: | Early Precambrian crystalline basement in the Songshan region, the south margin of the North China Craton （NNC）, mainly consists of the Neoarchean Dengfeng Group TTG gneiss, Paleoproterozoic Songshan Group quartzite and Neoarchean to Paleoproterozoic granitic rocks. The Wufoshan Group, covering on the Dengfeng Group and Songshan Group with angular unconformity, is mainly composed of quartz sandstone and minor silty shale and thin layer of limestone. The depositional age and provenance of the Wufoshan Group, the oldest sedimentary cover on the Archean-Paleoproterozoic crystalline basement, could provide constraints on the classification of the Proterozoic stratum and the Precambrian crustal evolution of the northern margin of the NCC. This study reports LA-ICP-MS U-Pb ages and Hf isotope compositions of the detrital zircon from two quartz sandstones of the Ma＇anshan Formation at the bottom of the Wufoshan Group. The youngest 207Pb/206Pb ages are （1732±11） Ma and （1655±22） Ma, respectively, contemporary with the Mesoproterozoic sedimentary stratum formed after Xiong＇er Group volcanic-sedimentary rocks. The 207Pb/206Pb ages of the detrital zircons range from 2816 Ma to 1655 Ma with 60% between 2100 Ma and 1800 Ma and 24% between 2500 Ma and 2100 Ma, indicating that sedimentary materials mainly sourced from Paleoproterozoic geologic bodies. Combined with detrital zircon studies on sedimentary rocks from other regions of the NCC, the Archean-Paleoproterozoic crystalline basement is the main source of the Mesoproterozoic detrital materials of the NCC. The 207Pb/206Pb ages peak at （1.93±0.10） Ga, indicate significant early Precambrain tectonic-thermal events in the Songshan region, in conformity with Paleoproterozoic metamorphism ages （~1.91 Ga）. All detrital zircons have obvious negative to moderately positive εHf（t） values from -14.3 to 4.6, with Hf model ages （T） ranging from 3672 Ma to 2363 Ma. Most T model ages are between 2.80 Ga and 2.50 Ga evolution lines of crust, indicating that Neoarchean is the main crustal growth period of the southern margin of the NCC. |
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| Keywords: | Wufoshan Group detrital zircon U-Pb age provenance North China Craton |
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