华北板块北缘东段古生代沉积特征及盆地演化

The eastern part of the northern margin of the north china platform is epicontinental accretional belt between Xingmeng block and closed South branch ocean of the Paleo-Asian Ocean. It's the hotspot of geological science research now. Many researches have been achieved of the tectonic evolution through the research of magmatite and metamorphite. However, it has not yet been extensively studied through the research of sedimentary petrology. Depositional system which reflects the denudation order and level of the provenance is the most complete geological record of the tectonic activity. In order to restore the metamorphic rocks to their original natures, analyze the lithofacies and sedimentary environment, this project will relies on the study of the lithology, texture, structure, palaeontological fossils, sedimentary sequence and stratigraphic contact based on large-scale field measurements, and relies on the descriptions of the mineral constituent and microstructure under the microscope. On the basis of the palaeontological fossils, sedimentary sequence, stratigraphic contact and isotope dating, this project will re-determine the inaccurate stratigraphic age. According to the research of rock and mineral analysis, major element, trace element and lanthanon analysis, it will be discussed about the type and origin of Paleozoic volcanic - sedimentary rock, the type of sedimentary basin and tectonic setting. In order to investigate the starting and ending time of collision, restore the distribution of trench-arc-basin system and collided process, this project will focus on the sedimentation analysis, combined with geochemical, isotope analysis , as well as the results of previous studies, based on the theory of constraints on the tectonic evolution of sedimentary evolution.

华北板块北缘东段是古亚洲洋南支洋古生代闭合后与兴蒙地块碰撞的陆缘增生带。前人从岩浆岩、变质岩入手对该区构造演化开展了大量的研究，目前是地学研究的热点地区。从沉积角度研究相对较少。沉积体系反映了物源区的剥蚀顺序及程度，是构造活动过程最完整的地质记录。因此，本项目拟通过对研究区古生界重点剖面实测，详细描述其岩性、结构、构造、古生物化石、沉积序列和地层接触关系，显微镜下观察其矿物组成、显微结构及构造，恢复变质岩原岩，分析其岩相和沉积环境。根据沉积序列和地层接触关系、古生物、同位素测年等，对时代尚不准确地层和哑地层的形成时代进行重新厘定。通过岩矿分析，主量、微量和稀土元素分析，对古生代火山-沉积岩的类型、成因、沉积盆地类型及构造背景进行探讨。从沉积学角度出发，结合地球化学、同位素分析，以及前人研究成果，利用沉积演化对构造演化约束理论，探讨该区碰撞拼合的起止时间，恢复沟弧盆体系的分布及碰撞拼合过程。

华北板块北缘东段位于中亚造山带东南缘，该地区古生代期间的构造演化与古亚洲洋的演化及最终闭合有密切联系。本项目通过对研究区古生代地层或侵入岩的野外调查和采样工作，根据沉积序列和地层接触关系、古生物资料、锆石U-Pb测年，对区内时代尚不准确古生代地层及部分侵入岩的形成时代进行了重新厘定，研究结果表明，大量曾被前人划入下古生界的地层实际上形成于晚古生代至中生代初，或是由不同时代、不同性质和来源的地质体组成的构造混杂岩，仅有极少的地质体被确认形成于早古生代；部分晚古生代地层的形成时代也与前人认识不同，例如延边地区部分曾被划入二叠系的地层的形成时代延伸至了三叠纪。结合岩相组合分析和岩石样品主微量元素、Sr-Nd同位素、锆石Lu-Hf同位素等地球化学分析，探讨了研究区古生代各时期沉积体系类型、特征和构造背景，研究结果表明，华北板块北缘东段在早古生代初就存在古大洋的俯冲，于早古生代末—晚古生代初发生了一次弧-陆碰撞，之后的中—晚泥盆世经历了碰撞后的伸展作用，并于早石炭世再次经历了古亚洲洋的俯冲，俯冲作用可能持续到晚二叠世之后，古亚洲洋沿长春—延吉一线最终闭合于中—晚三叠世甚至更晚。