大洋平板俯冲的数值模拟再现：洋–陆汇聚速率影响  

Numerical Modeling of Flat Subduction: Constraints from the Ocean-continent Convergence Velocity

作　　者：皇甫鹏鹏[1,2,3] 王岳军[3,4] 范蔚茗[4] 李忠海[2] 王喻鸣 周永智 

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学计算地球动力学重点实验室,地球科学学院,北京100049 [3]中山大学地球科学与地质工程学院,广东广州510275 [4]中国科学院青藏高原研究所卓越研究中心,北京100101 [5]广州市执信中学,广东广州510080

出　　处：《大地构造与成矿学》2016年第3期429-445,共17页Geotectonica et Metallogenia

基　　金：973项目(2014CB440901和2015CB856106);国家自然科学基金项目(41190073,41402165和41304071);中山大学中央高校基本科研业务费专项资金联合资助

摘　　要：利用地球动力学数值模拟方法探讨了洋-陆汇聚时,大洋岩石圈的绝对俯冲速率和上覆大陆岩石圈的向洋绝对逆冲速率对俯冲模式的影响,尤其是上覆大陆的向洋绝对逆冲速率与平板俯冲之间的关系。模型结果显示,对于年龄为40 Ma的含正常洋壳厚度的大洋岩石圈,在初始俯冲角度为现今洋–陆俯冲平均倾角的极小值(19°)条件下,低速大洋俯冲(绝对俯冲速率≤3 cm/a)且上覆大陆岩石圈向洋绝对逆冲速率≥1 cm/a时,具备形成平板俯冲的条件。当中–高速大洋俯冲(绝对俯冲速度>3 cm/a)时,在上覆大陆的绝对逆冲速率不小于俯冲速率时可以形成平板俯冲。当增加初始俯冲角度到平均倾角的极大值(36°)时,仅在低速大洋俯冲(绝对俯冲速率≤3 cm/a)且绝对逆冲速率达到10 cm/a时(自然界中基本不存在),才有可能出现平板俯冲,其他情况均表现为陡俯冲。我们的模拟结果表明:(1)较高的大洋岩石圈绝对俯冲速率更容易克服板间耦合作用力而有利于陡俯冲形成;(2)较高的上覆大陆绝对逆冲速率更有利于俯冲板片弯曲而趋向于平板俯冲形成;(3)上覆大陆朝向海沟的逆冲速率会在俯冲板片下方产生水平向陆的地幔流,绝对逆冲速率越大该地幔流越强烈,导致作用于板片下表面的水平剪切分量越大而有利于板片弯折和平板俯冲发生;(4)初始俯冲角度的增加对平板俯冲的形成起到强烈抑制作用。这些能被现今平板俯冲,如具相似洋–陆汇聚速率条件的南美洲西海岸平板俯冲实例所验证。2-D numerical modeling is used to investigate the effects of ocean-continent convergence velocity on the flat subduction dynamics. It aims to better understand how the absolute subduction velocity of the oceanic lithosphere and absolute overthrusting velocity of the overriding continental lithosphere influence the subduction mode, in particular how the absolute overthrusting velocity regulates the development of flat subduction. Numerical models are divided into two groups with the initial subduction angle of 19° and 36°, respectively. Numerical models with 40 Ma-aged oceanic lithosphere and initial subduction angle of 19° show that（1） under the condition of low oceanic subduction velocity（≤3 cm/a）, the flat subduction can be easily formed when the overthrusting velocity is no less than 1 cm/a;（2） under the condition of moderate to high oceanic subduction velocity（3 cm/a）, the flat subduction can occur only when the absolute overriding velocity is no less than the absolute subduction velocity. However, for models with initial subduction angle of 36°, the flat subduction occurs only when the absolute subduction velocity is no larger than 3 cm/a and the absolute overthrusting velocity reaches 10 cm/a. Large absolute subduction velocity can promote decoupling between the downgoing and overriding plates and thus favors the development of steep subduction. In contrast, larger absolute overthrusting velocity facilitates the slab bending and thereby contributes to the development of flat subduction. Additionally, flat subduction at a high velocity of the overriding plate is significantly correlated with the landward mantle flow beneath the slab, which can facilitate the upward bending of the slab. Our results are evidenced by the kinematic models of the flat subduction beneath the South America.

关 键 词：平板俯冲 数值模拟 俯冲速率 大陆岩石圈向洋逆冲速率 洋壳初始俯冲角度 

分 类 号：P542[天文地球—构造地质学] TE352[天文地球—地质学]