“清河镇群”年代地层学研究进展

Progress in the Study of Chronostratigraphy of the “Qinghezhen Group ”

本文根据“清河镇群”(或“开原岩群”)年代地层学研究新进展,即在上肥地剖面原划入北大沟组、吴家堡子组,尖山子水库大坝原划入北大沟组等地层中获得的岩浆结晶锆石(SHRIMP)年龄2497±27Ma、2522±17Ma,250±5Ma;在“白砬子组”(或“照北山岩组”)之建组剖面东杨木林子的大理岩(结晶灰岩)中获得震旦纪之微古植物化石——Stictosphaeridiumtortutosum,Synsphaeridiumsp.,Hystrisphaeridiumsp.等,结合前人研究成果和区域地质构造特征,提出清河断裂为华北板块(清原地块)与北部陆缘活动带(兴蒙或吉黑造山带)的界线,前人划分的“辽河群”或“清河镇群”或“开原岩群”是分布在不同大地构造单元内的、不同属性的地质体的拼合物。并重新划分为清河断裂带之南华北板块内的新太古代英云闪长岩和古元古代芦家堡子岩组;清河断裂带以北华北板块北部陆缘活动带的构造岩石地层—新元古代(震旦纪)西保安岩组、早寒武世佟家屯岩组和晚二叠世尖山子火山岩。

Based on progress made in the study on the chronostratigraphy of the ＂Qinghezhen Group＂ or ＂Kaiyuan Group＂, such as SHRIMP ages of 2497 q-27 Ma and 2522 q-17 Ma obtained from the Beidagou and Wujiapuzi Formations in the Shangfeidi section, SHRIMP age of 247.5 q-6 Ma from the Beidagou Formation at Jianshanzi reservoir dam, and fossils Stictosphaeridium tortutosum, Synsphaeridium sp., Hystrisphaeridium sp. discovered from recrystallised limestones of the Bailazi Formation （the Zhaobeishan Formation） at Yangmulinzi in the east of the type section, as well as information collected in previous studies, the writers put forward that the Qinghe Fault is the boundary between the North China Plate （Qingyuan terrain here） and its northern mobile belt （i. e. the Hinggan-Mongolia or Jilin--Heilong orogenic zone）. A new stratigraphic subdivision is proposed as follows： Neoarchean and Paleoproterozoic Lujiapuzi Formation in the south of the Qinghe fault, Neoproterozoic （Sinian） Xibao＇an Formation, Early Cambrian Tongjiatun Formation, and Late Permian Jianshanzi lava in the north of the Qinghe fault.