Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions

The East Qinling and adjacent cratonic regions belong to two geotectonicunits,the Sinokorean Subdomain including the Sinokorean Platform and itssouthern continental margin the North Qinling Belt,and the YangtzeanSubdomain comprising the Yangtze Platform and its northern continental mar-gin the South Qinling Belt.The Qinling region may thus be subdivided into twocontinental margin belts separated from each other by the Proterozoic Qinlingmarine realm,which did not disappear until Late Triassic.The convergentcrustal consumption zone,the megasuture between the two belts,lies betweenthe Fengxian-Shangnan line in the north and the Shanyang-Xijia line in thesouth and was much deformed and displaced through Mesozoic intracratoniccollision and compression.In the northern subdomain the Lower Proterozoic is representedby protoaulacogen volcano-sediments,the inner Tiedonggou Group and theouter marginal Qinling Group,which were folded and metamorphosed in theLuliangian orogeny,a general process of aggregation and s

Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions

The East Qinling and adjacent cratonic regions belong to two geotectonic units, the Sinokorean Subdomain including the Sinokorean Platform and its southern continental margin the North Qinling Belt, and the Yangtzean Subdomain comprising the Yangtze Platform and its northern continental margin the South Qinling Belt .The Qinling region may thus be subdivided into two continental margin belts separated from each other by the Proterozoic Qinling marine realm , which did not disappear until Late Triassic . The convergent crustal consumption zone ,the megasuture between the two belts ,lies between the Fengxian Shangnan line in the north and the Shanyang Xijia line in the south and was much deformed and displaced through Mesozoic intracratonic collision and compression. In the northern subdomain the Lower Proterozoic is represented by protoaulacogen volcano-sediments , the inner Tiedonggou Group and the outer marginal Qinling Group , which were folded and metamorphosed in the Luliangian orogeny ,a general process of aggregation and stabilization of the Early Proterozoic mobile belts between and around the Archaean nuclei. Genuine aulacogen occurred in the Middle Proterozoic and was represented by the Xionger rift volcanics . The Middle and Upper Proterozoic comprise the inner Guandaokou shelf sediments and the outer extensional" back- arc" Kuanping Group behind the Qinling island chain . Oceanic subduction from the south of the Qinling arc representing the Jinningian orogeny caused the folding of the Mid dle and Upper Proterozoic and emplacement of island arc-continent collision type of granite . After the Jinningian orogeny Late Sinian glacigene deposits formed the platform cover and the Erlangping back arc basin began to develop on the northern slope of the Qinling arc . In South Qinling the Lower Proterozoic Tongbe Group was probably an original marginal part of the Yangtze Platform . The passive margin began rifting in Middle Proterozoic with the formation of the inner Shennongjia aulacogen and the outer marginal Wudang aulacogen. Deformation of the Wudang and Douling groups indicating Jinningian Movement seemed to have been caused by a southward compression of the Tongbe Massif. Resumed rifting in the Sinian evidenced by the sedimentary facies pattern caused the northward separation of the Douling Massif, which formed part of the Fuping-Zhenan island chain , the northern boundary of the South Qinling Belt. In the western part of South Qinling , in the Hanzhong region , the Middle and Upper Proterozoic are represented by the Huodiya shelf sediments and the Xixiang marginal volcano sedimentaries , The Jinningian orogeny is well represented by the deformed Xixiang Group and the subduction pattern of magmatism from north to south in the Beiba area . It seems that the genuine arc-basin system in the continental margin and the aulacogen in the inner part of the platform began in the Middle Proterozoic (1800 Ma), which marks the beginning of a new tectonic megastage in lithosphere evolution.