The Formation Age And Tectonic Environment Of Metamorphic Sedimentary Strata In The Yudu-Xingguo Area,Southern Jiangxi Province

The Shenshan formation,Kuli formation and Shangshi formation in southeastern Jiangxi are a set of pyroclastic and clastic sedimentary rock assemblages.The Kuli formation is a set of pyroclastic and clastic sedimentary rock assemblages.The Shangshi formation and the Shenshan formation contain cherts.The contact between Shenshan formation and Kuli formation,Kuli formation and Shangshi formation is conformable contact.They have long been regarded as Neoproterozoic strata deposited along the submarine slope of the Nanhua rift trough.However,with some new age determination results being put forward,more and more scholars think that Cathaysia is a continuous trench-arc-basin system,which gradually amalgamated in the Paleozoic Silurian up to now.The analysis of the formation and evolution of Shenshan formation,Kuli formation and Shangshi formation in Yudu-Xingguo area,southern Jiangxi Province is an important link in the study of the early tectonic pattern in Cathaysia area.It is of great significance to study the regional tectonic background and even the early tectonic evolution of the whole Cathaysia by studying its rock characteristics,formation age and source tectonic background.Zircon U-Pb chronology yielded the latest ages of 554 ± 7Ma and 428 ± 6Ma in the Shenshan formation and the Kuli formation,respectively.Refer to the previous study of the age of 381 Ma in rhyolite,it is concluded that the Shenshan formation,the Kuli formation and the Shangshi formation in the Yudu-Xingguo area were formed during the Cambrian to Carboniferous period.The detailed field investigation in the Yudu-Xingguo area shows that the Shenshan formation is mainly composed of eruption-sedimentary facies,and the lithology includes pyroclastic rocks,clastic sedimentary rocks and a small amount of cherts belts.The Kuli formation consists of empty accumulation and ejectiondeposit,and the main rock types include pyroclastic rocks and clastic sedimentary rocks.The Shangshi formation is also composed of empty accumulation and eruptive facies.The main rock assemblage consists of pyroclastic rocks,clastic sedimentary rocks and a small amount of chert bands.Based on the analysis of occurrence,lithofacies and rock assemblages,the provenance of Shenshan formation,Kuli formation and Shangshi formation mainly come from the volcanic arc in the southeast.The geochemical analysis of the major elements and trace elements in the whole rock shows that the samples of Shenshan formation,Kuli formation and Shangshi formation belong to the potassium basalt-high potassium calc-alkaline series.The clastic sedimentary rocks were derived from andesitic and acidic magma.All fall into the island arc field.It was concluded that the samples of Shenshan formation,Kuli formation and Shangshi formation were formed in the background of island arc volcanoes.Combine all the above information,this study suggests that the Shenshan formation,the Kuli formation and the Shangshi formation in the Yudu-Xingguo area are typical back-arc sedimentary environments with typical island arc volcanic rock assemblages.The island arc is the Yudu-Shaowu arc,and the YuduShaowu arc has a typical trench-arc-basin system,and the activity stopping time of the Yudu-Shaowu arc no earlier than the early Carboniferous period.