江南造山带皖南地区历口群沉积相、物源和时代研究
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摘要
江南造山带东段皖南地区的历口群,通常被认为是Rodinia超大陆形成后的早期裂谷沉积,记录了扬子板块东南缘东段晋宁造山作用后皖南地区新元古代盆地演化。但迄今为止皖南新元古代地层同位素年代学数据仍比较欠缺,且对历口群缺乏典型剖面的沉积学研究,沉积物物源仍不清楚,制约了对扬子地块东南缘东段新元古代盆地演化的全面认识。因此,本文选取出露于江南造山带东段的镇头组和邓家组典型剖面,运用沉积学、地层学和锆石U-Pb年代学方法,系统分析历口群沉积相及其物源特征,认为历口群形成时代在820～760 Ma之间,镇头组形成于近岸水下扇环境,主要物源为双桥山群浅变质岩和与双桥山群岛弧岩浆活动有关的地区,邓家组形成于滨岸环境,主要物源来自于扬子板块内部,部分与南华系裂谷火山岩和双桥山群岛弧岩浆活动有关。本研究对新元古代江南次级盆地演化时限提供制约,为扬子地块东南缘新元古代年代地层格架的建立和盆地的重建提供重要依据。
The Likou Group of the Southern Anhui is generally considered to be sediments in an early rift valley after the formation of the Rodinia supercontinent in the eastern Jiangnan orogeny. It records the evolution of a Neoproterozoic basin in southern Anhui after the Jinning orogeny in the eastern margin of the Yangtze Block.However, the depositional age and sediment provenance of the Likou Group is poorly constrained, limiting our understanding of the evolution of Neoproterozoic basins in the eastern margin of the Yangtze Block. To address this problem, we studied the sedimentology, stratigraphy, petrology, and detrital zircon U-Pb geochronology of the Zhentou and Dengjia fromations of the Likou Group in the eastern part of Jiangnan orogen, in order to systematically analyze the sedimentary facies and sediment provenance of the Likou Group. It is concluded that the depositional age of the Likou Group is between ca. 820 Ma to ca. 760 Ma; the Zhentou Formation was deposited in nearshore fan facies with the main sediment source from metamorphic rocks of the Shuangqiaoshan Group and related to island arc magmatic rocks; the Dengjia Formation was deposited in shore facies, with the main sediment source from the Yangtze Block and Nanhua rift volcanic rocks. This study provides constraints on the evolution of secondary basins in the Neoproterozoic Jiangnan sub-region, and provides important basis for the establishment of the Neoproterozoic stratigraphic framework and the reconstruction of the basin in the southeastern margin of the Yangtze Block.
The Likou Group of the Southern Anhui is generally considered to be sediments in an early rift valley after the formation of the Rodinia supercontinent in the eastern Jiangnan orogeny. It records the evolution of a Neoproterozoic basin in southern Anhui after the Jinning orogeny in the eastern margin of the Yangtze Block.However, the depositional age and sediment provenance of the Likou Group is poorly constrained, limiting our understanding of the evolution of Neoproterozoic basins in the eastern margin of the Yangtze Block. To address this problem, we studied the sedimentology, stratigraphy, petrology, and detrital zircon U-Pb geochronology of the Zhentou and Dengjia fromations of the Likou Group in the eastern part of Jiangnan orogen, in order to systematically analyze the sedimentary facies and sediment provenance of the Likou Group. It is concluded that the depositional age of the Likou Group is between ca. 820 Ma to ca. 760 Ma; the Zhentou Formation was deposited in nearshore fan facies with the main sediment source from metamorphic rocks of the Shuangqiaoshan Group and related to island arc magmatic rocks; the Dengjia Formation was deposited in shore facies, with the main sediment source from the Yangtze Block and Nanhua rift volcanic rocks. This study provides constraints on the evolution of secondary basins in the Neoproterozoic Jiangnan sub-region, and provides important basis for the establishment of the Neoproterozoic stratigraphic framework and the reconstruction of the basin in the southeastern margin of the Yangtze Block.
引文
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杜建国,孙乘云,许卫,杜森官,王有生,谢建成,黄耀华,陶启云.2002.皖南地区葛公镇组砾岩性质及其构造含义.资源调查与环境,(2):107-112.
高林志,杨明桂,丁孝忠,刘燕学,刘训,凌联海,张传恒.2008.华南双桥山群和河上镇群凝灰岩中的锆石SHRIMP U-Pb年龄-对江
南新元古代造山带演化的制约.地质通报,10:1744-1751.
汪正江,王剑,江新胜,孙海清,高天山,陈建书,邱艳生,杜秋定,邓奇,杨菲.2015.华南扬子地区新元古代地层划分对比研究新进展.地质论评,61(01):1-22.
王剑.2000.华南新元古代裂谷盆地沉积演化)--兼论与Rodinia解体的关系.北京:地质出版社.1-146.
王剑,刘宝珺,潘桂棠.2001.华南新元古代裂谷盆地演化-Rodinia超大陆解体的前奏.矿物岩石,21(3):135-145.
王剑.2005.华南―南华系研究新进展-论南华系地层划分与对比.地质通报,24(6):491-495.
王剑,周小琳,郭秀梅,付修根,高永华.2013.华南新元古代盆地开启年龄及沉积演化特征--以赣东北江南次级盆地为例.沉积学报,31(05):834-844.
张彦杰,孙磊,周效华,廖圣兵,王存智,朱意萍.2010.皖赣相邻区新元古代构造演化探讨.地质学刊,34(04):351-357.
张彦杰,周效华,廖圣兵,余明刚,蒋仁,姜杨.2011.江南造山带北缘鄣源基性岩地质-地球化学特征及成因机制.高校地质学报,17(03):393-405.
周汉文,李献华,王汉荣,李江,李惠民.2002.广西鹰扬关群基性火山岩的锆石U-Pb年龄及其地质意义.地质论评,48(S1):22-25.
周金城,王孝磊,邱检生.2014.江南造山带新元古代构造-岩浆演化.北京:科学出版社.50-51.
周效华,张彦杰,廖圣兵,余明刚,陈志洪,赵希林,姜杨,蒋仁.2012.皖赣相邻地区双桥山群火山岩的LA-ICP-MS锆石U-Pb年龄及其地质意义.高校地质学报,18(04):609-622.
Andersen T.2002.Corrections of common lead in U-Pb analyses that do not report 204 Pb.Chem.Geol,192:59-79.
Li X H,Li Z X,Ge W C,Zhou H W,Li W X,Liu Y&Michael T D W.2003.Neoproterozoic granitoids in South China:crustal melting above a mantle plume at ca.825 Ma.Precambrain Research,122:45-83.
Ludwig K R.2001.SQUID 1.02.A User‘s Manual.Berkeley:Berkeley Geochronology Center Special Publication,19.
Wang J,Li X H,Duan T Z,et al.2003.Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China.Chinese Science Bulletin,16:1663-1669.
Wang X L,Zhou J C,Wan Y S,et al.2013.Magmatic evolution and crustal recycling for Neoproterozoic strongly peraluminous granitoids from southern China:Hf and O isotopes in zircon.Earth Plant.Sci.Lett.366:71-82.
Wang X L,Zhou X H,J C,Griffin W L,Wang R C,Qiu J S,O’Reilly S Y,Xu X S,Liu X M&Zhang G L.2007.Detrital zircon geochronology of Precambrain basement sequences in the Jiangnan orogen:dating the assembly of the Yangtze and Cathaysia Blocks.Precambrain Research,15(9):117-131.
Zheng Y F,Wu R X,Wu Y B,Zhang S B,Yuan H L&Wu F Y.2008.Rift melting of juvenile arc-derived crust:Geochemical evidence from Neoproterozoic volcanic and granitic rocks in the Jiangnan Orogen,South China.Precambrian Research,163:351-383.