Weak metamorphic rock series of Nanhua System widely distribute in South Anhui. They include Shangxi Group and Xikou Group. Shangxi Group can be divided into Xiangdong Formation and Yangzhanling Formation from bottom to top. The middle member of Yangzhanling Formation is composed predominantly of mudstones,siltstones and sandstones,and minor polymictic conglomerates. In this study,we take 11 samples of fine-grained clastic rocks from Zhentou profile in Jixi County and Gegongzhen profile in Dongzhi County where they are well-exposed to measure their geochemistry characteristics and discuss their provenance and tectonic setting. Relatively high Al2O3/TiO2 ratios(21.57 on average),LREE/HREE ratios(6.98 on average)and obviously negative Eu anomalies(Eu/Eu* =0.71 on average)of samples from both two profiles,combining with the TiO2 vs Al2 O3, TiO2 vs Zr,and La/Th-Hf plot,suggest that their provenance are dominantly felsic rocks. Indicators of CIA,CIW and PIA for these samples are small(71.6, 75.4 and 71.2,respectively),implying that their provenance suffered lower weathering. In addition,the geochemistry characteristic of this clastic rocks are similar to the granodiorites and volcanic rocks surrounding themselves and together with the new evidences of petrology and stratigraphy,we believe that these granodiorites and volcanic rocks would be the important source of these sedimentary rocks. The discrimination diagrams of tectonic setting based on major elements and trace elements and characteristic values of rare elements show the feature of both continental island arc and active continental margin,which may indicate that these rocks represent the infill of active continental back arc basin. This conclusion can be used to the Shangxi Group because the middle member of Yangzhanling Formation belongs to the component of transgression-regression sequence of Shangxi Group.
. Geochemical characteristics and its geological significance of fine-grained clastic sedimentary rocks in the middle member of Yangzhanling Formation of Nanhua System in South Anhui[J]. Chinese Journal of Geology, 2014, 49(2): 651-667.