| 郯庐断裂带南段张八岭群地层时代的重新厘定 |
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| 引用本文： | 蔡倩茹,牛漫兰,吴齐,苑潇宇,王婷,李秀财,孙毅.郯庐断裂带南段张八岭群地层时代的重新厘定[J].地质科学,2019,54(3):781-795. |
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| 作者姓名： | 蔡倩茹 牛漫兰 吴齐 苑潇宇 王婷 李秀财 孙毅 |
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| 作者单位： | 合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009;合肥工业大学资源与环境工程学院 合肥230009 |
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| 摘 要： | 扬子板块东北缘的浅变质岩被认为是三叠纪大陆俯冲过程中从扬子板块剥离而来的，其原岩主要为新元古代中期岩浆岩和沉积岩，是理解扬子板块东北缘新元古代构造演化的重要对象。郯庐断裂带张八岭隆起北段夹持于大别造山带和苏鲁造山带之间，出露一套绿片岩相—低角闪岩变火山—沉积序列，即由西冷组变火山岩和北将军组变碎屑岩组成的张八岭群。然而，西冷组与北将军组之间的关系和张八岭群的形成时代都尚存在争议。为此，本文对张八岭群开展了详细的野外地质调查和MC-LA-ICP-MS锆石U-Pb定年工作。锆石U-Pb定年结果显示，西冷组顶部石英角斑岩的原岩时代为723±7 Ma；北将军组底部变粉砂岩的碎屑锆石年龄变化于916～614 Ma之间，与西冷组、肥东杂岩内新元古代岩浆活动时间相一致，暗示它们的物质主要由西冷组和肥东杂岩提供，其中，最年轻碎屑锆石谐和年龄（677±12 Ma）限定了北将军组沉积时代下限。结合野外地质特征和前人张八岭群上覆震旦系盖层沉积初始时间（635 Ma），本文认为北将军组的沉积时限为677～635 Ma，是覆盖于西冷组之上的中新元古代晚期沉积地层。对比研究显示，张八岭群可能是扬子东北缘新元古代中期裂谷火山—沉积岩系的重要组成部分。
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| 关 键 词： | 郯庐断裂带 张八岭群 新元古代 浅变质岩 锆石U-Pb年龄 |
| 收稿时间： | 2019-03-10 |
Revisiting the formation age of the Zhangbaling Group in the southern segment of the Tan-Lu fault zone |
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| Cai Qianru Niu Manlan Wu Qi Yuan Xiaoyu Wang Ting Li Xiucai Sun Yi.Revisiting the formation age of the Zhangbaling Group in the southern segment of the Tan-Lu fault zone[J].Chinese Journal of Geology,2019,54(3):781-795. |
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| Authors: | Cai Qianru Niu Manlan Wu Qi Yuan Xiaoyu Wang Ting Li Xiucai Sun Yi |
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| Institution: | School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009 |
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| Abstract: | Low-grade metamorphic rocks are distributed continuously along the northern margin of the northeast margin of Yangtze block, and they are thought to be scraped off from the Yangtze plate during the Triassic continental subduction. Their protoliths were dominated by Mid-Neoproterozoic igneous and sedimentary rocks, which are important to understand the Neoproterozoic evolution of the northeast margin of Yangtze plate. The low-grade metamorphic rocks, namely Zhangbaling Group, were also identified in the northern Zhangbaling Tan-Lu fault zone located between the Dabie and Sulu Orogens. The Zhangbaling Group can be divided into the Xileng and Beijiangjun Formations, which were predominately composed of meta-volcanic and meta-clastic rocks, respectively. However, the formation age of the Zhangbaling Group and the relationship between the Xileng and Beijiangjun Formations are still controversial. To address this, a combined study of field investigation and MC-LA-ICP-MS dating were performed on the low-grade metamorphic rocks in the Zhangbaling Group. Zircon U-Pb datings gave a protolith age of 723±7 Ma for the quartz keratophyre from the top layer of the Xileng Formation, and yielded detrital zircon ages of 916～614 Ma with a cluster peaking at ca. 730 Ma for the meta-siltstone from the bottom of Beijiangjun Formation. The age distribution of the detrital zircons was identical with those of Neoproterozoic igneous rocks in Xileng Formation and Feidong complex, implying that the provenance of the Beijiangjun Formation was derived from the Xileng Formation and Feidong complex. The youngest detrital zircon age of 677±12 Ma provides a lower limit for the deposition age, and the geological occurrence of overlying Sinian system provides an upper limit of 635 Ma for the deposition age. This paper considers that the sedimentary age limit of the Beijiangjun Formation is 677～635 Ma, which was inferred that the Beijiangjun Formation covered on the Xileng Formation during late-stage of the Mid-Neoproterozoic. The comparative study shows that the Zhangbaling Group may be an important part of the volcanic-sedimentary rocks of the rift valley in the northeast margin of the Neoproterozoic. |
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