华北燕辽裂谷盆地中元古代构造古地理演化——来自蓟县地区下马岭组碎屑锆石年代学的证据

Mesoproterozoic tectonic and paleogeographic evolution of the YanliaoRift Basin in the northern North China Craton: Constraints fromdetrital zircon ages of the Xiamaling Formation in the Jixian area

燕辽裂谷盆地位于华北克拉通北部,记录了华北克拉通古元古代碰撞拼合之后的陆内伸展、中元古代Nuna超大陆裂解和全球大气海洋增氧等重大地质事件,但燕辽裂谷盆地中元古代古地理与构造演化研究一直较为薄弱。对该盆地蓟县地区下马岭组标准剖面开展了沉积学与碎屑锆石U-Pb年代学研究,获取了下马岭组地层沉积特征与碎屑锆石的U-Pb年龄。LA-ICP-MS锆石U-Pb定年结果显示下马岭组石英砂岩样品中的碎屑锆石207 Pb/206 Pb年龄范围为3270~1806 Ma,且展示2530 Ma和1880 Ma两个显著峰值,表明下马岭组碎屑岩地层主要由新太古代和古元古代晚期的碎屑物组成,而且这两个显著的年龄峰分别对应于华北克拉通新太古和古元古代两期重大地质事件。此外,另有少量~2750 Ma和3200 Ma的碎屑锆石,分别对应两期华北克拉通太古宙岩浆事件。碎屑锆石年龄分布特征显示下马岭组沉积于伸展背景。该文结合蓟县系和其下伏长城系沉积组合与盆地古地理分析,提出燕辽裂谷盆地的构造演化可大致分为4个阶段,分别是①碰撞后伸展转换阶段(1.85~1.60 Ga);②早期陆内伸展阶段(1.60~1.40 Ga);③对应于全球Nuna超大陆裂解事件的裂谷作用阶段(1.40~1.30 Ga);④整体抬升阶段(1.32~1.0 Ga)。

The Yanliao Rift Basin is located in the northern part of the North China Craton,which recorded the intracontinental extension following the Paleoproterozoic collision of the North China Craton,the breakup of the Nuna supercontinent,along with the Mesoproterozoic oxygenation event.However,studies on the Mesoproterozoic Paleogeography and tectonic evolution of the Yanliao rift basin is less studied.In this paper,we systematically investigated the sedimentary characteristics of the Jixian system in the Jixian area,and obtained detrital zircon U-Pb ages for the clastic rock samples from the standard stratigraphic section of the Xiamaling Formation of the Jixian system.LA-ICP-MS zircon U-Pb dating results show that the 207 Pb/206 Pb ages of detrital zircons from the Xiamaling Formation quartz sandstone samples range from 3270 to 1806 Ma,with two significant age peaks at 1880 Ma and 2530 Ma.The results show that the sandstone of Xiamaling Formation is mainly composed of detritus from Neoarchean and late Paleoproterozoic,and the two most significant age peaks correspond to the Middle Archean-Paleoproterozoic geological events in the North China Craton respectively.In addition,a few older detrital zircons(~2750 Ma and 3200 Ma)also occur,corresponding to Archean magmatic events in the North China Craton,respectively.The detrital zircon age distribution indicate that the Xiamaling Formation was deposited in an extensional setting.Given the sedimentary assemblages of the Jixian system and the underlying Changcheng System,we here conclude that the tectonic evolution of the Yanliao Rift Basin can be roughly divided into four stages:①The post-collision extensional transition stage(1.85~1.60 Ga);②Early intracontinental extension(1.60~1.40 Ga);③The rifting basin stage corresponding to the global breakup of the Nuna supercontinent(1.40~1.30 Ga);④Overall uplifting stage(1.32~1.0 Ga).