江南造山带皖南地区历口群沉积相、物源和时代研究

THE SEDIMENTARY FACIES,PROVENANCE AND DEPOSITIONAL AGE OF THE LIKOU GROUP OF SOUTHERN ANHUI IN THE JIANGNAN OROGEN

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.