Sedimentary Response Of The Proterozoic Xiong'er Aulacogen On The Southern Margin Of North China To The Breakup Of The Columbia Supercontinent

The North China Craton(NCC),which has experienced billions of years of evolution and preserved abundant geological event records,has been a hot research topic for many scholars.From late Paleoproterozoic to Mesoproterozoic,aulacogen/rift system deposits and tectonic-magmatic activities can be linked to the breakup of the Columbia supercontinent and have developed in the NCC.In this study,the Proterozoic Xiong'er Aulacogen on the southern margin of the NCC was comprehensively analysed to determine the evolution from the crystalline basement to the sedimentary caprock,and to explore the relationship of geological events within the background of the breakup of the Columbia supercontinent.Based on the characteristics of sedimentary rocks,lithologic associations,sedimentary evolution and geochronological characteristics,the evolution process of the Xiong'er Aulacogen can be divided into "three stages and two sequences".First,the basement sedimentary stage(1.83-1.75 Ga)consists of bimodal volcanic-sedimentary rocks of the Xiong'er Group with continental-marine facies and alluvial fan deposits of the Bingmagou Formation with local development.It represents the evolution of the intracontinental fault from initiation to decline.According to sedimentary succession and geochemical characteristics of the Bingmagou Formation,it is found that it is closely related to the Xiong'er Group and developed in the early stage of the aulacogen.After the southern margin of the NCC changed to the stage of stable continental margin,the Xiong'er Aulacogen entered the stage of filling deposition(1.75-1.6 Ga).It consists of transgressive-regressive sedimentary sequence I formed by the first-order relative sea level change,which is characterized as the largest range of marine deposition and covers the southern margin of the whole NCC.The filling sedimentary sequence is dominated by terrigenous siliciclastic sedimentary rocks with local carbonates deposits.Later,the early Mesoproterozoic tectonic-magmatic activities on the southern margin of the NCC resulted in significant paleogeographic differences in the Xiong'er Aulacogen.The sedimentary sequence II,which is formed by carbonates formations,indicates the sedimentary stage(1.6-1.4 Ga)of the caprock developed by later large-scale marine flooding event and shrinking process of the basin.The tectonic uplift event in the south margin of the NCC resulted in the Xiong'er Aulacogen gradually uplifted and exposed from the northeast to the southwest,and finally a hiatus of nearly hundreds of millions of years occurred.The study of typical sedimentary structures is helpful to the understanding of sedimentary environment and paleogeographic evolution of Precambrian strata.There are abundant MISS in the siliciclastic sedimentary rocks of the Ruyang Group in sedimentary sequence I.In this paper,MISS with different morphological characteristics in the Gaoshanhe and Ma'anshan Formations are newly discovered,which effectively indicate the sedimentary facies and its evolution.MISS are useful to isochronic correlation and connection of regional strata,and establishes isochronic stratigraphic framework of the Xiong'er Aulacogen.Through an understanding of the chronology and depositional environment of the MTS,unique sedimentary structures,is limited,based on the sedimentary features of the MTS,the Hejiazhai Formation corresponds to Neoproterozoic carbonate rocks(1.0-0.72 Ga)and is linked to the Neoproterozoic sedimentary strata of the Xuhuai Rift on the southeastern margin of the NCC.Based on stratigraphic contact,sedimentary evolution and geochemical characteristics,the sedimentary stratigraphic units in the Songji area are redefined and the previous Wufoshan Group is disintegrated.The Wufoshan Group only consists of the Ma'anshan and Putaoyu Formations,which developed in the Paleoproterozoic.The Luotuopan Formation which overlies the erosional unconformity is independent and belongs to Mesoproterozoic.The Hejiazhai Formation at the top of the previous Wufoshan Group is classified as Neoproterozoic.According to the lithologic characteristics,sedimentary structure,zircon ages,stratigraphic distribution and regional paleogeographic evolution,the age of Huanglianduo and Dongjia Formations should develop in the Mesoproterozoic(1.6-1.4 Ga).During the late Paleoproterozoic to Mesoproterozoic,the Xiong'er magmatic activities,the giant dykes(or large igneous provinces,LIPs),the A-type granites,and the sedimentary stages of " seesaw transition" of the Xiong'er Aulacogen and Yanliao Rift are coupled with the breakup of the Columbia Supercontinent.The extensional faulting event at about 1.8 Ga in the NCC indicates the initial faulting time of the Columbia Supercontinent,which drifts away from the supercontinent at 1.6-1.4 Ga.After 1.4 Ga,the NCC may have started the stage of geological evolution into the Rodinia Supercontinent.