太平洋板块俯冲与华北克拉通晚中生代岩石圈构造-热演化：数值模拟研究

Tectono-thermal modeling of the lithosphere can describe quantitatively the process of craton destruction, which also sets up an important bridge between the deep mantle processes and shallow geological responses. Destruction of the North China Craton is a product of continental lithosphere dynamics under the specific background, where the deep subduction of the Pacific Plate underneath East Asia is thought to have played a key role. Therefore, tectono-thermal evolution of the lithosphere should be studied in the subduction zone systems. Subduction zone system includes a subducting plate, a viscous asthenospheric mantle, and a solid overriding lithosphere, and the complex feedbacks among them influence greatly the tectono-thermal evolution of the lithosphere. This study aims to establish a two-dimensional dynamic subduction model in the plate-mantle-lithosphere system, numerically simulate the plate-mantle-lithosphere interaction by the finite-element method, and quantitatively reveal the lithospheric deformation and the thinning rate. This study not only pays attentions to the deep dynamic processes, but also the tectono-thermal responses in the shallow depth. It plans to investigate the dynamical mechanisms of the large-scale ductile deformation within the continental crust (metamorphic core complexes) and palaeo-heat flow peak appeared in the sedimentary basin, which was regarded as the structural and geothermal indicators of craton destruction, respectively. The objective is to explore the linkage between the deep processes and shallow geological phenomena. Constrained by the observed data, this study will reveal quantitatively the tectono-thermal evolution characteristics of the North China Craton in Late Mesozoic, and thus better understand the role of the subduction of the Pacific Plate and its interaction with the continental lithosphere evolution, as well as the geodynamical mechanism of the North China Craton destruction.

岩石圈构造-热演化模拟可定量描述克拉通破坏过程，是搭建深部地幔过程与浅部地质响应的桥梁。华北克拉通破坏是特定动力学背景下的产物，其中太平洋板块俯冲起着决定性的作用，因此华北岩石圈晚中生代构造-热演化应该置于俯冲带动力系统中研究。俯冲带动力系统包括俯冲板片、粘性软流圈地幔和上覆固体岩石圈，三者的相互反馈对岩石圈构造-热演化具有重要影响。本项目拟建立俯冲带动力模型，利用有限元技术模拟研究板-幔-岩石圈相互作用下华北克拉通的减薄速率及变形特征。在研究深部动力学过程的同时关注浅部构造-热响应，探讨华北克拉通破坏的构造学标志—以变质核杂岩为代表的区域伸展变形及地热学标志-盆地古热流峰值的成因控制。探索浅部地质与深部演化之间的内在关联，利用观测资料对数值模型进行约束，定量揭示华北克拉通晚中生代构造-热演化特征，从而更好地理解太平洋板块俯冲与大陆岩石圈的相互作用以及华北克拉通破坏的动力学机制。

项目综合分析了华北克拉通现今热流特征、岩石圈热结构，模拟研究了中新生代岩石圈构造-热演化特征及渤海湾盆地的形成，推测太平洋板块俯冲速度的变化和俯冲带的幕式东退作用对渤海湾盆地幕式伸展和伸展中心东移具有重要作用。基于地质与地球物理资料构建岩石圈二维伸展动力学数值模型，系统模拟地壳厚度、初始温度场等对岩石圈伸展形态的影响，并定量揭示出变质核杂岩冷却速率与伸展速率的关系；结合早白垩世渤海湾宽裂谷盆地特征以及边缘变质核杂岩热年代学数据，约束克拉通破坏时期的岩石圈初始温度场特征以及边缘伸展速率特征；探讨了以变质核杂岩为代表的区域伸展变形及地热学标志(盆地古热流峰值)的地球动力学机制。基于二维热-化学地幔对流模型，利用有限元技术模拟研究了板块俯冲、平卧及停滞过程中板块的热演化和水的运移特征，指出停滞在地幔过渡带的太平洋板块脱水会产生湿柱，湿柱到达岩石圈底部所导致的熔融可以解释东亚晚新生代板内火山的形成。该项目深入探索了浅部地质与深部过程之间的内在关联，定量揭示出华北克拉通晚中生代构造-热演化特征，从而更好地理解太平洋板块俯冲与大陆岩石圈的相互作用以及华北克拉通破坏的动力学机制。