大陆碰撞侧向逃逸和初始板块边界的形成

Lateral escape and formation of new plate boundaries during continental collision is controlled by different driving forces including lateral extrusion, slab rollback, gravity collapse and basal drag. However, the relative contributions of these driving forces in old orogenic belts such as the eastern Tethysides of Asia are difficult to distinguish and evaluate quantitatively, because many resulting structures may be overprinted by younger events. The Anatolian plate, located within the active collision zone between the Arabian and Eurasian plates in the west-central Tethysides, represents the early stage of collision, where different driving forces have acted at different times and in different directions, forming different suites of structure, basins, and resources. For example, new plate boundaries formed as the North- and East Anatolian Fault Zones, and are presently forming in the diffuse zone between the westward and southward moving parts of Anatolia. In order to analyze the interplay between these different processes and their relative contributions, we will apply varieties of geological methods, including field structural analysis, microstructure, petrology, and thermochronology, to determine the history of surface structural deformation and geodynamic mechanisms of partial melting of the lower crust, and combine these studies with characterization and interpretation of deep geophysical characteristics to quantitatively assess the contribution from deeper mantle processes. Geodynamic numerical modeling will use the results from our geological and geophysical studies to obtain a physically realistic, geologically constrained 4D evolution model for lateral escape and formation of new plate boundaries during continental collision. This research will deepen the understanding of the geodynamic mechanism of tectonic escape and the mechanism of plate boundary initiation during continental collision in active and ancient orogens.

大陆碰撞过程中侧向逃逸和新板块边界的形成受侧向挤出、板片回撤、重力垮塌和底部拖曳等驱动力控制。但古老造山带（如东特提斯）各驱动力相对贡献因后期构造叠加难以区分和定量评估。西特提斯安纳托利亚处于阿拉伯—欧亚板块碰撞早期，多种驱动力主导的时间、方位，产生的构造、盆地和资源组合各不相同。如沿北、东安纳托利亚断层的新转换板块边界已经形成，而在安纳托利亚内部向南、西运动区域之间的过渡区，正生成初始伸展板块边界。为区分和定量评估四种驱动过程之间相互关系和贡献，拟对该区运用构造解析、显微组构、岩石学和热年代学等方法，定量约束浅部构造变形史和下地壳部分熔融地球动力学成因，结合深部地球物理特征和地球动力学数值模拟，定量评估地幔深部过程贡献，构建符合实际的大陆碰撞侧向逃逸及新板块边界形成4D演化模型。该研究有利于对比中-西-东特提斯大地构造演化，加深理解新、老造山带内构造逃逸动力学机制和板块边界初始形成机制。

本项目聚焦特提斯地球动力系统重大研究计划的核心科学问题“地球多陆块单向聚合动力学”其中的关键环节-俯冲起始和初始板块边界形成机制。研究对象为特提斯部土耳其安纳托利亚板块以及中国境内特提斯域。安纳托利亚处于阿拉伯—欧亚板块碰撞早期，利于我们对侧向逃逸和新板块边界形成的四种驱动力（侧向挤出、板片回撤、重力垮塌和底部拖曳）的相互关系和贡献定量评估，研究内容涉及定量约束浅部构造变形史和下地壳熔融地球动力学成因，结合深部地球物理特征，定量评估地幔深部过程贡献，进而对比中-西-东特提斯大地构造演化，加深对于新、老造山带内构造逃逸动力学机制和板块边界初始形成机制的理解。获得以下新认识：.1..首次报道北祁连东段俯冲起始岩石记录，为上覆板片岛弧/弧前杂岩的俯冲提供直接证据；提出上覆板片俯冲在减少俯冲初始岩石记录上扮演重要角色，可解释古老造山带内为何稀缺俯冲初始岩石记录；.2..安纳托利亚板块浅部运动学特征受深部构造机制控制，GPS水平位移场在安纳托利亚板块中部以西向运动为主，由碰撞挤出控制；而在其西部运动学特征向西南大幅偏转，由海沟回撤控制；.3..西安纳托利亚中新世钙碱性英安岩和第四纪碱性玄武岩之间Ca同位素比值差异达0.1%，表明俯冲折返阶段岩浆源区性质发生巨大改变；结合地球物理剖面，提出海沟回撤过程中软流圈地幔沿板片撕裂构造窗上涌是主要因素；.4..门德列斯地体北部混合岩形成年龄与门德列斯变质核杂岩体同时代，可能与希腊海沟回撤形成变质核杂岩和热物质上涌造成的降压熔融有关；南部混合岩则是变质核杂岩伸展促使基底深熔岩的出露。.5..地球物理研究结果显示土耳其地壳厚度与大地构造背景存在关联，东部碰撞加厚，中部过渡，西部伸展减薄。.综上，本项目对新生板块边界的要素进行基本限定，大致确定了初始板块边界位置，探讨了不同大地构造驱动力对安纳托利亚的相对贡献。11篇论文发表在Geology,GSA Bulletin, Tectonophysics, Scientific Reports等国内外知名期刊（NI文章1篇），另外还有10篇处于审稿阶段。