Timing And Provenance Analysis Of Wolegen Group In Xinlin-jiagedaqi Area,Northern Great Xing'an Range

The Central Asian Orogenic Belt is the largest accretionary orogenic belt in the world,and the related scientific issues of continental accretion and intracontinental reconstruction make it the most typical research object in exploring the continental dynamics and thus receives extensive attention.Northeast China is situated in the eastern part of the Central Asian Orogenic Belt,where there are still considerable controversies over the basement attributes,the timing of amalgamation of micro-blocks and the process of ocean-continent transitions.The study of epimetamorphic rock series of Wolegen Group in Northeast China has attracted the attention of many scholars.Therefore,in this thesis,we carry out many research works of the rocks in Xinlin-Jiagedaqi area,including the detailed field geological survey,petrology and petrography,detrital zircon LA-ICP-MS U-Pb geochronology analysis,analysis of the main trace geochemical elements of the whole rock and so on,to analyze the sedimentary age and provenance of the epimetamorphic rock series,provide the key evidence for the amalgamation time of the Erguna Block and the Xingan Block.Moreover,new constraints on the tectonic background of the sedimentary formation output of the early Paleozoic in the region were put forward.LA-ICP-MS technique was used to determine the U-Pb age of zircon from the samples collected in the study area in this study.The results showed that the minimum detrital zircons obtained from the quartz sandstone of Jixianggou Fm in Jifeng forest farm area are 443 Ma in age and 503 Ma in minimum peak age;the minimum age of detrital zircons obtained from the strip argillaceous siltstone samples of Jixianggou Fm in Dayangqi forest farm was 470 Ma and the minimum peak age was 487 Ma.The minimum age of the detrital zircon suggests that the Jixianggou Fm of the Wolegen Group deposited before the Middle Ordovician.The weighted average age of silicified foliated tuff samples of Dawangzi Fm in Guyuan forest farm is 482±3 Ma MSWD=0.02;the weighted average age of phyllitic slate samples of Dawangzi Fm on the west side of the Dawusu forest farm is 493±3 Ma,MSWD=0.65;the weighted average age of the metamorphic andesite samples of Dawangzi Fm in Dausu forest farm is 419 ± 3 Ma,MSWD=1.4;Moreover the age of pyroclastic rock samples indicated that the magmatic crystallization age of Dawangzi Fm of the Wolegen Group is in the Late Silurian.Based on the existing data in this area,it was considered that the Sedimentation of the Wolegen Group might be a set of complex rocks deposited from Cambrian to Late Silurian.It is inferred that the material source of the Wolegen Group is mainly from the Erguna massif and partly from the Dobaoshan volcanic arc according to the analysis of Hf isotope characteristics and age spectrum of the samples.Petrographic characteristics show that the protolith of epimetamorphic rock series in the Wolegen Group is a set of terrigenous clastic sedimentary rocks.Geochemical analysis and geochemical data mapping suggested that the Wolegen Group was of typical characteristics of active continental margin,and the Dawangzi Group metamorphic volcanic rocks may be a set of volcanic rocks of back-arc basin-active continental margin.Thus,we speculate that,the southeastern margin of the Erguna Block was an active continental margin in the Early Ordovician.During the Ordovician-Silurian Period,the southeastern part of the Erguna Block opened along the Xinlin-Toudaoqiao Suture Zone.Xinglong-Huma back-arc basin was formed between the Erguna Block-Xingan Block and the Duobaoshan Island Arc Belt,and the volcanic clastic rock deposited.However,the Wolegen Group is widely distributed and scattered,and whether the selected samples can represent the composition of the rock series still needs to be further discussed,and its formation background needs to be studied deeply.