The Sedimentary Facies,Provenances And Formation Age Of The Likou Group Of The Southern Anhui In Jiangnan Orogen

This paper study on the Neoproterozoic sedimentary strata of south Anhui in the eastern Jiangnan orogen.We chose Likou sections which has good outcrop,primary and well-preserved sedimentary structure and clear sedimentary rock sequence basically.The main purpose is to analyze provenance and obtain formation age.Based on the standpoint of sedimentary basin analysis,we used gravel statistical analysis,sandstone detrital clasts component analysis and zircon U-Pb chronology methods to analyze the provenance and formation age in detail and systemically.According to lithology analysis and characteristics of lithofacies combination,it was considered that the Gegongzhen formation formed in subsea apron facies,the Zhentou formation formed in the nearshore fan facies and the Dengjia formation formed in the shore facies,the Puling formation is basic volcanic rock and formed in eruptive facies.According to the statistical analysis of the Laohukeng gravel,it was concluded that the shallow-metamorphic rocks of the Shuangqiaoshan group and the area related to the island arc magmatic provided the main material source;In the triangular diagram,the sandstone data of the Dengjia formation concentrated in recycled orogenic,indicating the Yangtze block was the main source area.Statistics of the detrital zircon showed the Dengjia formation contained ancient debris which were formed in the early Mesoproterozoic,indicating a plenty of material are from the Yangtze block;the ages of the young detrital zircon are near or consistent within the range of error with the Jingtan formation obtained from bimodal volcanic-sedimentary rift,indicating the source area was Nanhua rift volcano rocks,and a small amount of detrital zircons which were about 820 Ma showed the provenance was related with Shuangqiaoshan island arc magmatism.The LA-ICP-MS U-Pb zircon ages obtained in tuffs of the Zhentou formation are 820±10Ma;the youngest group of detrital zircon U-Pb ages are 789±11Ma.Combined with the isotopic age data(760Ma)of the Puling formation which was published in the Likou group is previously,we proposed that the time span of the formation of the Likou group is older,the main body of the Zhentou formation deposited at about 820 ± 10 Ma,and the Dengjia formation deposited during 760Ma~789Ma.This age data provided the time basis for accurately calibrating the location of the Likou group in the Neoproterozoic stratigraphic column.Therefore,the opening time of Jiangnan sub-basin was basically the same as the South China Neoproterozoic rift system,and the time of beginning to deposit was also about 820Ma.