海拉尔盆地晚中生代构造伸展的转换过程及其地球动力学意义

The parts played by the evolution of Mongolia-Okhotsk orogenic belt and the subduction of the paleo-Pacific plate on the Late Mesozoic tectonic extension in NE China, are still controversial nowdays. The Hailar Basin, which was possibly affected by both of the two dynamic systems, is selected as a case study in this application. Integrated research methods will be used to clarify the extensional stages and their transition in the basin during the Late Mesozoic, including: Geological survey, to distinguish clearly and authentically the contact relationship between the critical sedimentary and volcanic layers; Seismic interpretation and Balanced Structural Section Analysis, to study the geometry and kinematics of the structural deformation and reveal the structural stretching characteristics and superimposed relationship, and recovery the structural history of the Hailar Basin; Syn-rifting igneous rocks geochronology, geochemistry and Sr-Nd-Pb isotope analyses, to determine the time of extensional transition and magmatism in the Hailar Basin, their properties, magma sources and evolutionary chacacteristics, and to discuss deep geological process of Late Meosozoic extension and extensional transition. Finally, the variation of the regional extensional deformation will also be analyzed through the correlation between the Hailar Basin and its adjacent areas in NE China. The goal of this study is to unclose the geodynamic significance of the Late Mesozoic extension and extensional transition of the Hailar Basin, which is attributed to the change from a tectonic domain of evolution of Mongolia-Okhotsk orogenic belt to the other controlled by the subduction of the paleo-Pacific plate during the Late Mesozoic.

当前地学界关于蒙古-鄂霍次克造山带和古太平洋板块俯冲两大构造体系的演化对中国东北晚中生代构造伸展产生的影响等还存在不同认识。本申请选择大地构造位置特殊的海拉尔盆地为研究对象，将野外地质调查与盆地研究相结合，在详细解剖盆地构造特征与岩浆事件的基础上，重点探讨海拉尔盆地晚中生代构造伸展的特征、转换过程及其地球动力学意义。通过地震解释和构造剖面平衡恢复研究，分析盆地构造演化史，阐明盆地不同伸展阶段的构造几何学、运动学特征及构造转换过程；系统开展同裂陷期火山岩的年代学、地球化学和Sr-Nd-Pb同位素等分析，厘定晚中生代构造伸展转换的时间，阐明不同伸展阶段火山岩的性质、源区与岩浆演化特征，探讨构造伸展与转换的深部地质作用过程；结合邻区构造伸展事件的对比分析，揭示区域上构造伸展的时空规律，探讨海拉尔盆地晚中生代构造伸展转换与蒙古-鄂霍次克造山带、古太平洋板块俯冲两大构造体系演化的关系及其动力学含义。

通过三维地震资料的构造解析和构造平衡恢复研究，定量揭示了海拉尔盆地贝尔凹陷早白垩世两期不同方向构造伸展变形特征及其叠加过程，即早期主要受控于北东东或近东西向控陷断裂，而晚期则总体受北东-北北东向断裂的控制，反映了区域构造伸展方向在125Ma左右发生重要转变。首次在海拉尔盆地识别出早白垩世早期挤压变形事件，提出该事件可能是蒙古-鄂霍次克洋闭合后进入强烈陆内造山作用的构造变形记录，为深入探讨晚中生代区域构造伸展的动力学成因提供关键信息；火山岩年代学研究表明海拉尔盆地晚中生代火山作用时代介于163-98Ma；岩石学和地球化学研究表明，晚中生代火山活动总体形成于板内伸展构造背景，但明显存在两个重要的阶段，即晚侏罗世（163-149Ma）火山作用可能主要受蒙古-鄂霍次克洋闭合后俯冲板片的断离拆沉有关，早白垩世（142-98Ma）火山作用可能受蒙古-鄂霍次克海造山带垮塌和古太平洋板块俯冲后撤两大构造体系的联合控制；提出海拉尔盆地早白垩世两期不同方向构造伸展叠加转换可能与晚中生代两大动力体系转换有关，即早期伸展可能与蒙古-鄂霍茨克造山后垮塌伸展有关，而晚期则由古太平洋板块俯冲拆沉、后撤引起的弧后伸展主导。