俯冲－碰撞转化带板片深部形态与地质响应

This study will provide solid evidence for the key question “Dynamics of single-directed continental amalgamation” of the major research plan “Tethyan Geodynamics”. Plate convergent zone consists of oceanic subduction zone and continent-continent collisional belt. It is the most intense area for mass recycling, the most active zone for volcanic and earthquake activities, and the most fertile place for natural mineral and oil-gas resource on Earth. The transition from oceanic subduction to continental collision is an inevitable and a key process of the Wilson cycle. However, previous studies paid much attention to either subduction zones or collisional belts. Therefore, it still remains elusive how oceanic subduction transfers to continental collision. This proposal focuses on the eastern Zagros collisional belt and western Makran subduction zone in Iran to unravel the detailed transition process from subduction to collision. Firstly, we plan to construct the fine 3D structure image of the subducting slab and the overriding plate through broadband seismic array observation in the study area. This seismic structure image will be combined with age information of the ophiolitic mélange to deduce the slab evolution through time. Then, we propose to systematically compare the nature of magmatism, deformation style and exhumation rate to acquire key geological features of the overriding plate. Finally, we will combine the new geophysical and geological data to understand the deep dynamic processes and their shallow responses, and to elucidate the tectonic coupling between the subducting slab and the overriding plate during the subduction-collision transition.

本研究能够对重大计划的核心科学问题“地球多陆块单向聚合动力学”提供直接观测证据。板块汇聚带是地球物质能量交换最强烈、火山-地震活动最活跃、矿产油气资源最丰富的区域。在板块汇聚带的演化过程中，俯冲板片的角度、组成、年龄等控制着地幔流动状态和过程、控制着汇聚带上盘板块的构造样式和演化。本项目聚焦伊朗莫克兰俯冲带-扎格罗斯碰撞带过渡区域，以大洋俯冲－大陆碰撞转换的精细过程为关键科学问题。首先，通过网格式流动地震台站观测手段获得该地区俯冲板片深部精细三维结构，结合造山带内蛇绿混杂岩年代信息，反演俯冲板片的四维演化特征。同时，通过翔实的野外观察和室内分析，详细对比扎格罗斯碰撞带和莫克兰俯冲带典型岩浆岩性质、构造变形及隆升剥露特征，获得俯冲板片上盘地质演化关键信息。综合上述信息，认识俯冲-碰撞转换的深部构造过程和浅部响应，理清大洋俯冲向大陆碰撞过程中，俯冲板片和上盘岩浆活动、变形及造山作用的耦合关系。

本项目以大洋俯冲－大陆碰撞转换的精细过程为关键科学问题。聚焦伊朗莫克兰俯冲带-扎格罗斯碰撞带过渡区域，结合网格式流动台站观测手段和翔实的野外地质观测和室内地质和地球化学分析，理清大洋俯冲向大陆碰撞过程中，俯冲板片和上盘岩浆作用、变形及隆升作用的耦合关系，从而为重大计划的核心科学问题“地球多陆块单向聚合动力学”提供直接观测证据。项目首次获得俯冲-碰撞转换带俯冲板片深部精细结构。结果清晰的展示出大陆碰撞过程中深部大洋岩石圈如何与大陆岩石圈分离的过程，在此过程中地表造山运动和岩浆作用如何响应。其次是通过地球物理-地质学的多学科观测，理清了新特提斯洋上万公里的蛇绿岩所能代表的科学意义，即：洋中脊俯冲的痕迹，挑战了前人就蛇绿岩代表俯冲起始的认识。第三，构建特提斯“单程列车”模型与维持列车运行的关键环节，并提供了关键环节的地质观测实例，使得模型得以完善。项目执行至今紧密围绕项目主题共刊出23篇同行评议论文，包括国际SCI论文21篇，国际专著章节1章，中文论文1篇， 第一资助率43.47%。目前被Nature Geoscience, Science Adavances, Review of Geophysics, Geology, EPSL等顶级专业杂志引用。荷兰地质学家van Hinsbergen教授在其文章中将本项目观点来支撑其立论 (van Hinsbergen等, 2021, Nature Geoscience)。国内外著名的地球动力学团队专门针对我们提出的假说进行数值模拟验证，比如欧洲科学院院士Phlippe Agard教授团队（Larvet et al., 2022 EPSL）专门针对我们有关洋中脊俯冲造成被动大陆边缘裂解进行了地球动力学数值模拟验证；美国伊利诺伊大学Liu Lijun教授就我们陆块拼贴导致俯冲带跃迁的观点运用在欧亚大陆东缘的陆块拼贴与演化方面(Liu等, 2021 Earth-Science Reviews)。