| 三维板块几何形态对大陆深俯冲动力学的制约 |
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| 引用本文： | 李忠海,石耀霖.三维板块几何形态对大陆深俯冲动力学的制约[J].地球物理学报,2016,59(8):2806-2817. |
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| 作者姓名： | 李忠海 石耀霖 |
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| 作者单位： | 计算地球动力学重点实验室, 中国科学院大学地球科学学院, 北京 100049 |
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| 基金项目： | 国家重点基础研究发展计划项目（2015CB856106），国家自然科学基金项目（41590860，41304071），中国科学院战略性科技先导专项B（XDB18020104）和中组部青年千人计划项目联合资助. |
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| 摘 要： | 大陆深俯冲及超高压变质作用是大陆动力学的重要研究内容,前人进行了系统的地质、地球物理观测以及数值模拟研究.然而,自然界中大陆板块的俯冲、碰撞及造山过程大部分具有明显的沿走向的差异性,这种典型的三维特征可能很大程度上依赖于会聚大陆板块的初始几何学和运动学特征.本文采用三维高分辨率的动力学数值模拟方法,建立了方形大陆板块和楔形大陆板块两种不同的俯冲-碰撞模型,并且俯冲大陆板块侧面与大洋俯冲带相邻.数值模拟结果揭示大洋板块可以持续地俯冲到地幔之中,而大陆板块俯冲到一定深度处,其前端的俯冲板块将发生断离,并进而造成残余的大陆板块俯冲角度的减小.方形大陆俯冲板块的断离深度约为150km,而楔形大陆俯冲板块的断离深度较大,约250~300km,这很大程度上取决于俯冲带中大洋板块的牵引力和大陆板块的负浮力之间的竞争关系.同时,无论方形还是楔形大陆板块俯冲模型中,板块断离后,侧向的大洋俯冲板块仍可以拖曳约60~70km宽的大陆边缘岩石圈持续向下俯冲,揭示了新西兰东部的洋-陆空间转换俯冲带的动力学机制.并且,数值模型与喜马拉雅造山带和秦岭—大别—苏鲁造山带进行了对比,进而对其高压-超高压岩石空间展布沿走向的差异性特征和机制提供了一定的启示.
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| 关 键 词： | 大陆俯冲 超高压变质 板块几何形态 数值模拟 喜马拉雅 大别-苏鲁 |
| 收稿时间： | 2015-08-02 |
Constraints of 3-D plate geometry on the dynamics of continental deep subduction |
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| LI Zhong-Hai,SHI Yao-Lin.Constraints of 3-D plate geometry on the dynamics of continental deep subduction[J].Chinese Journal of Geophysics,2016,59(8):2806-2817. |
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| Authors: | LI Zhong-Hai SHI Yao-Lin |
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| Institution: | Key Laboratory of Computational Geodynamics, College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | Investigations of continental deep subduction and Ultra-High Pressure (UHP) metamorphism play significant roles in better understanding the continental geodynamics. Thereby, a number of geological and geophysical observations, as well as numerical simulations, have already been conducted systematically. However, along-strike variations are commonly observed in continental subduction/collision zones and mountain belts in nature. These three-dimensional (3-D) characteristics may be strongly dependent on the initial geometry and kinematics of converging continental plates. In order to study this problem, we have conducted 3-D high-resolution numerical models of subduction with rectangular or wedge-shaped continental plates, in which the subducting continental plate is laterally neighbored by oceanic subduction zone. The results demonstrate that oceanic subduction is continuous; however, slab break-off occurs in the continental subduction zone, after which the dip angle of the residue continental slab is decreased. In the model with rectangular continent, slab break-off occurs at around 150 km depth; whereas in the wedge-shaped continental subduction model, the depth of slab break-off is larger at about 250~300 km. The different phenomena are mainly attributed to the competing effects between the upward negative buoyancy of subducting continental slab and the downward drag from along-strike neighboring oceanic slab. In addition, after slab break-off, no matter in the model with a rectangular or wedge-shaped continent, a narrow continental marginal lithosphere (60~70 km in width) can keep going with the subducting oceanic slab to the mantle. This provides a good explanation for the continental sliver subduction dragged by neighboring oceanic subduction in New Zealand. The numerical models are also compared with the Himalaya and Qinling-Dabie-Sulu mountain belts, which provide significant implications for the along-strike variation in distributions of HP-UHP metamorphic rocks. |
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| Keywords: | Continental subduction UHP metamorphism Plate geometry Numerical modeling Himalaya Dabie-Sulu |
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