Analysis Of Tectonic Setting Of Late Paleozoic In Yimianpo Region, Heilongjiang Province

The Yimianpo Region in this paper refers to the region where from Yimianpo,Shangzhi City to Sanhe station, Heilongjiang Province. The region is located in the easternsegment of the Mongolia-Hinggan Orogen Belt, which is in the south of the binding site ofSongnen block and Jiamusi block. Xunke-Tieli-Shangzhi Fracture is the west boundaryline of the region.Bureau of Geology and Mineral Resources of Heilongjiang Province defined sandyand slate as Gu’antun Formation and defined calcalkaline volcano rock as EtoushanFormation, which of them were Yimianpo Group, forming in the Neoproterozoic.In progress of studying on petrology and strata in Heilongjiang Province, scholardisintegrated the Yimianpo Group, dividing the Gu’antun Formation into XinxingFormation, Zhangguangcai Range Group and dividing the Etoushan Formation intoKuanhe Formation, which of them formed in the Neoproterozoic.In the studying of geological survey in the field, author discover Gu’antun Formationis different from Xinxing Formation in rock association and geochronology, so authorsuggest that it belongs to Yimianpo Group. This paper analyze the tectonic setting latePaleozoic with geochronology, rock association and geochemistry of Gu’antun Formationand related granite in Yimianpo region. 1. Rock associations and geochronology of the Gu’antun FormationThe rock associations of Gu’antun Formation were defined as spotted slate,carbonaceous slate, argillaceous siltstone and silt argillaceous rocks by Regional Ggeologyof Heilongjiang Province. Field geological observations and petrographic studies showthat the rock associations of Gu’antun Formation were not complete previously, that thepresence of pyroclastic material in its upper part of the rock, and the appearance ofpyroclastic rocks in its lower part.Zircon LA-ICP-MS U-Pb dating results indicate that the formation age of crystal tuffrock which interbeds in epimetamorphic rocks in upper Gu’antun Formation is258.0±1.6Ma (MSWD=0.113), belonging to the Late Paleozoic Late Permian and theyoungest206Pb/238U age of cuttings crystal tuff in the lower Gu’antun Formationconcentrated in274~283Ma,32zircon located in the zircons age range,206Pb/238Uweighted average age of281.6±1.6Ma (MSWD=0.072), represents the forming agebelongs to Early Permian. In addition, multitudinous capture zircons have its concordiaages (peak aged:2.5~1.3Ga,561~559Ma,483.7±3.5Ma,476±9Ma,408~406Ma,385±8Ma,349.4±2.8Ma,309.6±3.8Ma). These results indicate that the formation ofYimianpo Group Gu’antun Formation is not Neoproterozoic which was setted by theprevious, which should be the product after the Late Paleozoic Late Permian. The studyalso shows that the geological bodies of ancient Proterozoic may exist in surface of studyarea in the later stages of the Late Paleozoic.2. Geochronology and Geochemistry of Late Paleozoic graniteZircon LA-ICP-MS U-Pb dating results indicate that the formation age of Yanbolinggranite is262.0±1.5Ma,(WSMD=0.25), belonging to the Late Paleozoic Late Permian. Itbelongs to high-K calc-alkaline series rocks, with the characteristics of quasi-aluminous-rich peraluminous. In the diagram of SiO2-Ce, all samples points fall into ‘I-type’ granites,which is similar to typical I-type granites.3. Tectonic setting of the Late Paleozoic in Yiminpo areaStudying on the major and trace elements data, from epimetamorphic rocks, pyroclastic rocks and Yanboling granite in the region, the results indicate that the LatePaleozoic Gu’antun Formation and Yanboling granite formed under the active continentalmargin tectonic setting.In the diagram of SiO2-K2O/Na2O, most samples points fall into the activecontinental margin tectonic setting. Early Permian Gu’antun Formation pyroclastic rocksare characterized by enrichment in large ion lithophile elements (LILEs, such as Ba, K, U,Rb) and light rare earth elements (LREEs), depletion of high field strength elements andheavy REE (HREEs), which is similar to the volcanic rocks from the active continentalmargin setting. Meanwhile, the geochemical data of Yanboling granite has thecharacteristics of ‘I-type’ granites. Combined with the tectonic setting of the LatePaleozoic in the eastern of the Jiamusi block, it is concluded that Gu’antun Formation andYanboling granite formed under an active continental margin tectonic setting, which mayrepresent the subduction of the Paleo-Asian Ocean underneath the Jiameng blocks.