华北克拉通北缘东段“开原岩群”的解体及重新认识

DISINTEGRATION AND REUNDERSTANDING OF THE “KAIYUAN ROCK GROUP” IN THE EAST SECTION OF THE NORTHERN MARGIN OF NORTH CHINA CRATON

根据近年来的同位素年代学资料,对分布于辽北地区的一套构造变质岩系("开原岩群"或"清河镇岩群")进行了重新认识和划分,并将其重新定义为清河构造混杂岩,由中太古代、新太古代、中元古代、新元古代、二叠纪等不同时代、不同构造环境的地质体组成.其中,中太古代、新太古代、中元古代岩石来自华北克拉通,而新元古代、二叠纪岩石则来自兴蒙造山带.将原沈家堡子岩组重新划分为新太古代变质表壳岩和中—新太古代变质深成岩,原板石沟岩组(或芦家堡子岩组)厘定为中元古代石门岩组,原照北山岩组重新划分为新元古代南平岩片和晚二叠世照北山岩组,将原佟家屯岩组和尖山子火山岩合并为晚二叠世佟家屯岩组.最后,提出了清河构造混杂岩带为华北克拉通与兴蒙造山带的界线以及古亚洲洋在华北板块北缘东段的最终闭合时间为中三叠世早期(约245 Ma)的认识.

According to recently obtained isochronologic data,the authors have a new understanding of the tectonic metamorphic rock series,formerly known as＂Kaiyuan rock group＂or＂Qinghezhen rock group＂,in northern Liaoning Province,and redefine it as Qinghe tectonic melange. It consists of the Mesoarchean,Neoarchean and Mesoproterozoic rocks from North China Craton,and also the Neoproterozoic and Permian rocks from Xing＇an-Mongolian orogenic belt with various tectonic conditions. The original Shenjiapuzi rock formation is redivided into Neoarchean metamorphic supracrustal rocks and Meso-Neoarchean metamorphic plutonic rocks;while the original Zhaobeishan rock formation into Neoproterozoic Nanping slices and Late Permian Zhaobeishan rock formation. The original Banshigou rock formation（or Lujiapuzi rock formation） is redefined as Mesoproterozoic Shimen rock formation. The original Tongjiatun rock formation and Jianshanzi volcanic rock are combined into the Late Permian Tongjiatun rock formation. Finally,the authors suggest that the Qinghe tectonic melange belt be the boundary between North China Craton and Xing＇anMongolian orogenic belt,and the final closing time of Paleo-Asian Ocean in the east section of northern margin of North China plate should be the early Middle Triassic（ca. 245 Ma）.