江南造山带中段新元古代构造演化——来自碎屑锆石U⁃Pb和Lu⁃Hf同位素的启示  

Neoproterozoic Tectonic Evolution in the Middle Segment of the Jiangnan Orogenic Belt:Implications from detrital zircon U-Pb and Lu-Hf isotopes

作　　者：蔡欣豫 王伟 田洋 CAI XinYu;WANG Wei;TIAN Yang(State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;Wuhan Center of China Geological Survey(Geosciences Innovation Center of Central South China),Wuhan 430205,China)

机构地区：[1]地质过程与矿产资源国家重点实验室,中国地质大学(武汉)地球科学学院,武汉430074 [2]中国地质调查局武汉地质调查中心(中南地质科技创新中心),武汉430205

出　　处：《沉积学报》2024年第6期1986-2005,共20页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42272228,41972242);霍英东教育基金(171013)。

摘　　要：【目的】厘定湖南地区新元古代沉积地层的沉积时代、物源和构造背景,是理解江南造山带中段构造演化过程的关键要素。【方法】开展野外考察并采集6件江南造山带中段冷家溪群、板溪群的碎屑岩样品,通过研究碎屑锆石形态、微量元素以及U-Pb和Lu-Hf同位素组成,并结合已有的碎屑锆石数据与可能的源区特征进行对比,限定沉积地层的物源组成及盆地构造演化历程。【结果】冷家溪群形成于852~825 Ma,板溪群形成于820~720 Ma。冷家溪群、板溪群最主要的碎屑锆石年龄峰值为920~790 Ma,冷家溪群还包括1750~1620 Ma、2500~2450 Ma的年龄峰值,板溪群包括1950~1790 Ma、2420~2330 Ma的年龄峰值。Hf同位素特征显示冷家溪群主要接受来自扬子地块的物源,板溪群在扬子地块和华夏地块拼合之后开始沉积,除了扬子地块的物源可能还有来自华夏地块的沉积物供给。【结论】冷家溪群沉积于沟弧盆体系下的弧后盆地,在825 Ma后弧后盆地关闭,伴随沉积地层内发育的强烈褶皱以及大量S型花岗岩侵入褶皱基底中。板溪群沉积于碰撞后伸展作用并发育陆内裂谷的构造背景,同裂谷岩浆作用集中发生于780~760 Ma,裂谷作用于板溪群沉积结束逐渐减弱。[Objective]Determining the depositional age,sedimentary sources and tectonic background of Neoproterozoic sedimentary strata in Hunan province is one of the keys to understanding tectonic evolution in the middle segment of the Jiangnan orogenic belt.[Methods]Six clastic rock samples were collected from the Lengjiaxi Group and Banxi Group in the middle segment of the Jiangnan orogenic belt.Provenance and tectonic setting of the sedimentary basins were determined by studying the morphology,trace elements,and U-Pb/Lu-Hf isotopic composition of detrital zircons,and collating published data for detrital zircons and zircons from source areas[.Results]The results indicated that the Lengjiaxi Group was formed at about 852825 Ma,and the Banxi Group was formed at about 820720 Ma.The most important detrital zircon age peaks in the Lengjiaxi Group and Banxi Group occur at 920790 Ma;age peaks also appear at 17501620 Ma and 25002450 Ma in the Lengjiaxi Group,and at 19501790 Ma and 24202330 Ma in the Banxi Group.The Hf isotopic characteristics show that the Lengjiaxi Group mainly received sediments from the Yangtze Block,and the Banxi Group received detritus from both the Yangtze and Cathaysia Blocks.[Conclusions]The U-Pb and Lu-Hf isotopic compositions of detrital zircons indicate that deposition in the Lengjiaxi Group and Banxi Group occurred before and after the amalgamation of the Yangtze and Cathaysia Blocks,respectively.The Lengjiaxi Group was deposited in the back-arc basin of a trench-arc-basin system which was closed by 825 Ma accompanied by strong folding in the sedimentary strata and a large number of S-type granite intrusions.The Banxi Group was deposited in an intraplate rift setting related to post-collision extension.Rifting-related magma erupted around 780760 Ma,and gradually weakened along the sedimentation of the Banxi Group.

关 键 词：新元古代 江南造山带 冷家溪群 板溪群 碎屑锆石 

分 类 号：P597[天文地球—地球化学]