华北克拉通太古宙典型地区栖霞县幅1:5万地质图修编——野外地质调查和SHRIMP锆石U-Pb定年

摘要

栖霞是胶东早前寒武纪变质基底的典型地区.在原1:5万地质图中,许多TTG岩石都被作为胶东群表壳岩看待,岩石形成时代也只在少数露头被确定.根据野外地质调查和SHRIMP锆石U-Pb定年,对该区TTG岩石时空分布进行了研究.在新修编的1:5万地质图中,太古宙变质基底的主要岩石类型为约2.9Ga、约2.7Ga和约2.5Ga的英云闪长质片麻岩,也存在少量同时代的奥长花岗质片麻岩.2.9Ga和2.5Ga左右的表壳岩(黄崖底表壳岩和胶东群)比原认为要少得多.所有岩石大致呈北西西—南东东向分布,它们在空间上共存,可能是新太古代晚期和古元古代晚期强烈构造热事件作用的结果.这是国内首次在复杂的太古宙高级变质岩区,以野外地质调查和SHRIMP锆石U-Pb定年有机结合,确定不同类型、不同时代地质体时空分布的有益尝试,对于今后类似地区开展专题地质填图具有重要的借鉴意义.%Qixia is a typical area of Early Precambrian basement in eastern Shandong, North China Craton. Many TTG rocks were once considered to be supracrustal rocks (the Jiaodong Group), and the formation ages of the rocks have only been determined in a few outcrops in the original geological map (1:50000) of the area. In this study, the authors carried out geological mapping and SHRIMP U-Pb zircon dating on more than 30 samples in order to determine the temporal and spatial distribution of the TTG rocks. In the newly compiled geological map (1:50000), the main rock types of the Archean basement are tonalite gneisses with ages~2.9Ga, ~2.7Ga and ~2.5Ga and some local trondhjemite gneisses of the same ages. Supracrustal rocks of ~2.9Ga and ~2.5Ga (the Huangyadi supracrustal rocks and the Jiaodong Group) are very rare. All of the rocks roughly extend in a NWW-SEE direction, probably as a result of the strong late Neoarchean and late Paleoproterozoic tectonothermal events.