新特提斯洋起始张开与起始俯冲的动力学数值模拟

The Tethyan tectonic domain experienced complex evolution history, including continental rifting and seafloor spreading, multiple oceanic subduction and terrane accretion, as well as the final continental collision and mountain building. In this project, the geodynamic numerical modeling, coupled with thermodynamic data, will be applied to systematically investigate two principle scientific questions, i.e. the initial opening of oceanic basin and the plate subduction initiation. For the dynamics of oceanic basin opening, three models are previously proposed: back-arc spreading, passive continental margin extension, and mantle plume driving. The dynamics of subduction initiation may be either spontaneous or induced, occurring in the intra-oceanic setting or the passive continental margin. Based on these studies, we will firstly focus on the driving mechanism of the initiation of opening and subduction of the Neo-Tethys oceanic basin, which will assess the mechanical feasibility of the different models. Secondly, the geological responses and characteristic rock records will be quantitatively simulated in the numerical models, which will be further compared with the observational data in the Tethyan domain. Finally, the dynamic modes of both opening and subduction initiation of the Neo-Tethys oceanic basin will be well constrained. These two geodynamic problems are the key controlling points for the Tethyan system, which are also crucial for better understanding and further developing the theory of Wilson circle and plate tectonics.

特提斯构造域经历了复杂的演化过程，既包含大陆板块的裂解及新生洋盆的形成，又包含多期次大洋板块的俯冲、多地体的拼合以及最终的大陆碰撞和造山。本项目拟采用动力学数值模拟（耦合热力学数据）的方法，聚焦新特提斯大洋板块形成和消亡的起始过程，对‘洋盆起始张开’和‘板块起始俯冲’这两个关键科学问题进行系统研究。对于新特提斯洋盆的起始张开，前人提出的概念模式包含弧后扩张、被动陆缘伸展和地幔柱推动三种。对于板块的起始俯冲，一般包含洋内和被动陆缘两种模式，各自又包含自发和诱发两种可能的机制。对此，本项目首先聚焦洋盆起始张开和板块起始俯冲的动力学驱动机制，探讨不同模式的力学可行性；而后，定量化的模拟计算这两个起始过程的地质响应和特征岩石记录，进而与特提斯构造域的观测数据进行对比；最终，提出各自最符合的动力学模式。这两个起始问题不仅是控制特提斯动力系统的关键，也对于发展威尔逊旋回和完善板块构造理论具有重要意义。

特提斯系统经历了漫长的演化历史，包含了多期次的威尔逊旋回，是研究板块构造与地球动力学的理想对象。特提斯演化的典型特征是一系列大陆块体从南方的冈瓦纳大陆裂解，而后向北漂移，最终与北方的劳亚大陆碰撞拼合。该过程中，多期次特提斯洋盆(原特提斯洋、古特提斯洋、新特提斯洋)的张开和关闭是核心要素。本项目以大洋板块的生命周期为主线，将特提斯系统演化分解为四个关键动力学过程：大陆裂解、俯冲起始、洋脊俯冲、大陆碰撞，并系统分析了每个关键过程的控制因素和驱动力。(1)特提斯系统窄条形大陆地体的裂解可能受控于板块俯冲、尤其是俯冲板片的远端牵引作用；而块状印度大陆的裂解及印度洋的张开可能是地幔柱与远端俯冲板块共同作用的结果。(2)特提斯系统周期性的大陆地体碰撞拼合产生多期次的俯冲跃迁，是地体碰撞产生的反推力、洋脊推力及板下地幔流牵引力共同作用的结果，并且岩石圈的弱化是关键因素。(3)洋脊俯冲往往伴随着板片断离，该构造体制的转换可能需要地幔流牵引力的辅助，从而实现板块俯冲的延续性；而洋脊俯冲对上盘和下盘都会产生一定的动力学效应，其特征地质记录可用于反演洋脊俯冲历史。(4)青藏高原的巨大重力势能意味着持续至今的印藏碰撞需要洋中脊推力之外的驱动力，大尺度地幔流牵引力可能具有重要贡献；未来可能的北印度洋俯冲起始将释放汇聚应力而导致青藏高原垮塌。基于上述四个关键动力学过程及其驱动力的整合，我们提出了特提斯演化的“多引擎驱动”模型；即多期次特提斯大洋板块的北向俯冲提供了地体北漂的主要驱动力，但在地体碰撞拼合或洋脊俯冲等关键动力学节点上，俯冲板片断离导致板片拉力短缺，而洋脊推力和大尺度地幔流牵引力等可诱发新的板块俯冲起始，从而驱动特提斯系统的持续、单向裂解-聚合过程。