Detrital-zircon Geochronology From The Yangjiagou Formation In Southern Section Of Zhangguangcai Range And Their Geological Significance

Yangjiagou formation in southern section of Zhangguangcai range is the research object.Through field geological investigation,rock chemical analysis and LA-ICP-MS U-Pb isotopic dating of detrital zircon,determine the distribution and Yangjiagou formation rock assemblage and sedimentary formation of lower limit age.Contrast statistics and analysis of Yangjiagou detrital zircon U-Pb age with the age of iconic tectono magmatic events in Zhangguangcai range to find the source of detrital material.Study the geochemistry of Yangjiagou group rocks to analyse the features of provenance and formation environment of Yangjiagou group.After collation and analysis of zircon U-Pb age distribution of Paleozoic geological bodies in Zhangguangcai range,contrast it with age characteristics of detrital zircon in Yangjiagou formation and geological bodies with the same or similar age in the region to determine the significance of zircon peak ages in Yangjiagou formation anf Zhangguangcai range.The Yangjiagou formation is a set of epimetamorphic sand slate assemblages in the Xinzhan to Shangying in the north of Jiaohe city,Jilin province.The main rock types include slate and carbonaceous slate and silty slate,phyllitic slate and phyllite.LA-ICP-MS zircon U-Pb dating results show that the youngest surface age of single grain zircon in the fine sandstone detrital zircon of Yangjiagou formation is 264±7 Ma,which belongs to the end of Middle Permian.It shows that the lower limit of the Yangjiagou formation time is not earlier than the end of the Middle Permian.At the sametime,the formation time of the Yangjagou formation is limited to the Late Permian to the early Triassic,because of the late Triassic strata and intrusive Indosinian granites.There are 3 peak ages,484±7Ma,345±5Ma and 265±2Ma,corresponding to the early Paleozoic orogeny age,the early Palaeozoic early continental block age and the late Paleozoic active continental margin magmatic thermal event age.The single grain zircon surface age of 1489 grains of Paleozoic geological bodies in the Zhangguangcai range is concentrated at 2 maximum peaks: 253 Ma and 265 Ma.The former corresponds to the peak period of the early Paleozoic orogenic age with orogenic granite(mylonitize granite and granitic mylonite)and peak metamorphic age corresponding to the active continental margin;the latter with Mudanjiang ocean to Jiamusi late Paleozoic terrane of I type granite,arc volcano rock and volcano clastic rocks and metamorphic gabbro and amphibolite amphibolite is generally consistent with age.The Carboniferous is an intermittent period between zhangguangcailing area early Paleozoic orogeny and late Paleozoic tectonic process,during this period cracking occurred between Jiamusi massif and Songnen massif which had spliced in early Paleozoic,this leads to the creation of Late Paleozoic Mudanjiang ocean,Tangjiatun bimodal volcanic rock is representative geological body for this process.