朝鲜半岛平南盆地地质演化综述

Review on geological evolution of the Pyongnam basin in Korean Peninsula

平南盆地位于朝鲜半岛中部,处于华北克拉通(中朝克拉通)东缘;其演化历史长达10亿年,其地质记录为揭示东亚现今构造格局的形成提供重要制约。盆地发育中元古界-中生界,从下至上包括黄海群(1.3~1.1Ga)、祥原超群(1.0~0.9Ga,自下而上包括直岘群、祠堂隅群、默川群和灭岳山群等)、燕滩群(狗岘系,0.72~0.54Ga)、黄州系/超群(0.52~0.46Ga,包括下部黄州群和上部法洞群)和平安超群(0.33~0.24Ga)等5个构造层序;各单元之间均为平行不整合;沉积跨度超过10亿年,沉积物厚度累计达到15000m。另外,平南盆地南部发育临津群(0.42~0.35Ga),该地层与中元古界上部-奥陶系很可能呈构造接触关系。平南盆地沉积中心自中元古代晚期从南部逐渐向北部转移,新元古代及早古生代均位于中部,二叠纪盆地沉积中心位于北部。平南盆地沉积碎屑锆石年龄则显示物源发生多期变化:中元古代以盆地北侧基底~1.8Ga峰期岩浆-变质作用岩石为主;中元古代晚期以同沉积就位的岩浆岩为主;新元古代以1.6~1.5Ga和1.2~1.1Ga峰期的岩浆岩为主;寒武纪以~2.5Ga和~1.8Ga峰值的变质基底岩石为主。以上变化反映了古地理格局的显著变化。推测新元古代早期及之前,华北克拉通曾与某个发育1.6~1.5Ga和1.2~1.1Ga岩浆作用的克拉通或者岩浆弧相邻(近邻或远邻);地层记录了迄今所知新元古代最早的碳同位素负漂移(默川负漂移,~0.92Ga),地层可能还记录了最晚的负漂移(燕滩负漂移,可能对应全球Gaskiers负漂移,~0.55Ga),它们可能是对新元古代全球长期多次岩浆-裂解-冰期事件的响应。

The Pyongnam basin locates in the middle of the Korean Peninsula on the eastern margin of the North China(Sino-Korean)craton.It has a geological evolution history of over one billion years,and it gives critical constraints on the forming of the tectonic framework of East Asia.It developed Upper Mesoproterozoic-Neoproterozoic strata,which comprise five tectonic sequences:the Hwanghae Group(1.3~1.1Ga),the Sangwon Supergroup(Jikhyon,Sadangu-Mukchon-Myoraksan groups:1.0~0.9Ga),the Yontan(Kuhyon)Group(0.72~0.54Ga),the Hwangju Supergroup(Hwangju and Bopdong groups/bottom up:0.52~0.46Ga),and Pyongan Supergroup(0.33~0.24Ga).There're parallel disconformities among the five sequences with a depositional age range of over one billion years and a total stratigraphic thickness of up to 15000 meters.In addition,there's the Rimjin Group(0.42~0.35Ga)tectonically sitting on some of the Late Mesoproterozoic to Ordovician sequences on the southern margin of the basin,and it is likely thrusted stratigraphic slices.The depocenter was shifted northward from the very south during Late Mesoproterozoic,and was to the middle during Neoproterozoic-Early Paleozoic,and was to the north during Permian.The provenances deduced from detrital zircon U-Pb ages show multiple-stages,i.e.,dominated by the ca.1.8Ga crystalline basement in the Middle Mesoproterozoic,changed to a proximal contemporaneous igneous provenance in the Late Mesoproterozoic,then 1.6~1.5Ga and 1.2~1.1Ga igneous rocks at Neoproterozoic,and then back to basement-dominated rocks at the Cambrian.The provenancial shifts may represent the paleogeographic switches;and it is proposed that the craton was probably connected with a craton or an arc which contains predominantly 1.6~1.5Ga and 1.2~1.1Ga igneous rocks during and before the Early Neoproterozoic.During the period,the sediments in the basin record the ever-known earliest Neoproterozoic negative carbon drifting(Mokchon drifting,at ca.0.92Ga),and the latest of the period(Yontan Group,at ca.0.55Ga,possibly corresponding to the global Gaskiers event),and these may be a result of a prolonged magmatism-breakup-glaciation event during Neoproterozoic.