Mesoproterozoic Stratigraphic Characteristics And Sedimentary Paleogeography In South Margin Of The North China Craton

The issues of age attribution of the Mesoproterozoic sedimentary strata,regional paleogeographic pattern and tectonic evolution in the southern margin of the North China Plate have been heatedly explored in recent years.This study reports U-Pb geochronology and characteristics of zircon trace elements of detrital zircons from the Yunmengshan Formation of the Ruyang Group and the Huanglianduo Formation in the Lushan-xiatang area of the western Henan Province.The weighted average age of the youngest batch zircons of the Yunmengshan Formation is 1658±63Ma,and which limited the earliest sedimentary age of the Ruyang Group is no earlier than 1700Ma.This study reports U-Pb geochronology and characteristics of trace elements of detrital zircons from the Gaoshanhe Group in the Lingbao-Fudi area of the western Henan Province.The ²⁰⁷Pb/²⁰⁶Pb age of the youngest zircon of the Gaoshanhe Group is 1685±39Ma.Combined with the the weighted average age of the youngest six zircons of the Gaoshanhe Group in Maxia area of Gansu Province is 1680±55Ma,The formation age of the Gaoshanhe Group was also limited no earlier than 1700Ma.Combined with the chronological calibration of the Luoyukou Formation?1611¹638Ma?in the Ruyang area and the chronological calibration of the Longjiayuan Formation?1594±12 Ma?,The formation age of the Ruyang Group-the Luoyu Group and the Gaoshanhe Group were limited to 1700¹600Ma,which is the middle and late period of the Mesoproterozoic Changcheng period,corresponding with the international Statherian Period.The 207Pb/206Pb ages of the detrital zircons of the Yunmengshan Formation?the Gaoshanhe Group and the Huanglianduo Formation range from 1644Ma to 3179Ma,presenting six age peaks of 1850Ma,2100Ma,2300Ma,2500Ma,2670Ma and 2900Ma,corresponding to the Middle Archean-palaeoproterozoic geological events of the North China Craton?NCC?.The provenance of the Yunmengshan Formation is dominated by the 1850Ma peak age geological body,and the Huanglianduo Formation and the Gaoshanhe Group are the2500Ma peak age geological body.According to the comparison of age frequency of detrital zircons in the Gaoshanhe Group and Yunmengshan Formation,it is speculated that there are 2500Ma geological bodies reported less frequently in the west of the western Henan area.Based on the features of sedimentary rocks and sedimentary structures ofoutcrops,it indicates that the sedimentary facies of the Mesoproterozoic Changcheng System in the southern margin of the North China Craton include braided river facies,meandering river facies,estuary bay,barrier coast facies,no-barrier coast facies and neritic facies.The Mesoproterozoic Changchneg System strata is divided into six third-order sequences.It is in the SQ₄ that there occurred the Mesoproterozoic Changchneg System's largest marine-flooding event.The barrier coast facies and no-barrier coast facies mainly developed in the northwest,while the no-barrier coast facies and neritic facies developed in the southeast.From north to south,the terrain gradually decreases.The northwest and northeast of the ancient land of North China were mainly provenance.The spatial configuration relationship of sedimentary system was mainly controlled by landscape and source supply.In the early stage of sedimentation,due to the influence of landscape,a barrier-tidal environment developed in the uplift area,while a no-barrier coast environment developed in a flat terrain.In the later stage of sedimentation,due to the influence of source supply,a barrier-tidal environment developed in front of the injection site of debris material.There is a good correspondence of sedimentary characteristics in the Mesoproterozoic Changchneg System between the southern margin of the North China Plate and the northern of the North China Plate,and occurred a significant transgression in the middle of the Period of the Changchneg System.According to the geochemical characteristics of the Xionger Group volcanic rocks and their corresponding zircons,the sedimentary characteristics of the Xionger Group sedimentary rocks and the basin's tectonic attributes,it indicates that the early Mesoproterozoic Changcheng period is formed in the post-arc basin symbiotic with the"island arc".According to the Sedimentary Paleogeography and tectonic background,it indicates that the middle Mesoproterozoic Changcheng period is formed in the Coastal shallow sea deposits of the back-arc basin near the continent of Passive continental margin,which represents the stable continental inland source area.The late Mesoproterozoic Changcheng period was the transition period from the back-arc basin to the land surface basin.