Geochronology,Geochemistry,and Tectonic Implications Of The Meta-sedimentary Rocks From The Jiangyu Group In Yanbian Region,Jilin Province

In this study,we present detrital zircon U-Pb ages and Hf isotopic analysis data and whole-rock geochemical data from the meta-sedimentary rocks of the Jiangyu Group in the Yanbian region,southeastern margin of the Xing'an-Mongolian Orogenic Belt.The sedimentary age the nature,and the tectonic setting of the Jiangyu Group,and the early Paleozoic tectonic evolution in the Yanbian area are discussed,on the basis of an integrated analysis of petrography,geochemistry,zircon U-Pb-Hf isotopes,and previous research results.Through the analysis of the geochemical characteristics of the meta-sedimentary rocks of the Jiangyu Group,all samples are depleted in heavy rare earth elements(HREEs)and large ion lithophile elements(LILEs;e.g.,Rb,Sr and Ba),and enriched in light rare earth(LREEs)and high field strength elements(HFSE;e.g.,Ta,Y,and U),combined with a variety of protolith reconstruction,tectonic environment and source analysis,the metamorphic rocks of the meta-sedimentary rocks of the Jiangyu Group are paraceous rocks,which are mainly sedimentary rocks with sandstone,and contain a small amount of shale and clay rocks,and its provenance originates from continental arc environment related to active continental margin.The cathodoluminescence images of zircon show that the detrital zircons are mostly euhedral to subhedral,and some zircon grains are rounded to subrounded,and some contain inherited core-rim textures.The Th/U ratios are between 0.11 and 1.54 which is suggestive of magmatic zircon.Two samples of meta-sedimentary rocks from the Jiangyu Group yielded concordant ages ranging from 2926 Ma to 415 Ma,which can be divided into four groups:415 to 504 Ma,562 to 657 Ma,889 to 1347 Ma,and 1442 to 2926 Ma.The youngest detrital zircon age of the sample is 415 to 438 Ma(YC1?=426�3 Ma),which limits the maximum formation age of its the protoliths of the meta-sedimentary rocks,so the age of the protoliths of the meta-sedimentary rocks should not be earlier than the late Silurian.Combined with the 40Ar-39Ar ages of 406 Ma from the overlying metamorphic ophiolitic melange,these data indicate that the protoliths of the Jiangyu Group were deposited during late Silurian-Early Devonian time.Therefore,the meta-sedimentary rocks of the Jiangyu Group may be closer to 406-426 Ma,that is,the early Devonian and late Silurian,not the Precambrian,Cambrian or Carboniferous Permian,which were considered by the predecessors.The comparison of the U-Pb age and Hf isotopic data of detrital zircons between northeastern Gondwana and the Jiangyu Group indicates a probable tectonic affinity.The whole-rock geochemical data indicate that the protoliths of the meta-sedimentary rocks from the Jiangyu Group were graywackes deposited in a continental arc setting.Based on the existence of coeval subduction-accretion events along the eastern segment of the northern margin of the North China Craton(NCC),we infer that subduction-accretion events may have occurred in the Yanbian area followed by one or more arc-continent collisions after the early Devonian.