大洋板块运动方向反转控制活动陆缘岩石圈张裂过程数值模拟

Numerical Studies on Continental Lithospheric Breakup in Response to the Extension Induced by Subduction Direction Inversion

为了更好的探究大洋板块运动方向反转与大陆岩石圈张裂之间的动力学关系,以数值模拟为手段来正演大洋板块的反向俯冲,同时考虑光滑洋壳、海山链、海底高原、薄弱带等构造单元加入先期俯冲时对大陆岩石圈张裂的影响.结果显示:大陆岩石圈在大洋板块反向俯冲的过程中会被拉伸减薄,并出现局部岩石圈的颈缩直至张裂、同时伴随有软流圈地幔的上涌和减压熔融等现象.此外,含有不同构造单元的洋壳参与先期俯冲会对陆缘造成不同程度的破坏,从而影响拖曳过程中大陆岩石圈的应变集中,并导致大陆岩石圈在不同时间、不同位置出现张裂.模拟结果可用于对比南海陆缘在新生代张裂中表现的穿时等特征,亦可为其他被动陆缘张裂的动力学研究提供借鉴.

In order to investigate how the extension induced by subduction direction inversion affects the continental breakup,we conduct numerical simulation to represent the subduction process in the early stage and the extension induced by subduction direction inversion in the later stage. Meanwhile,different geological bodies,such as oceanic plate with smooth surface,seamount chains,oceanic plateau and weak zone,are added in the model during the early subduction stage. Results show that the extension induced by subduction direction inversion would cause lithospheric thinning,necking and breakup,being accompanied by asthenospheric upwelling and partial melting due to decompression. In addition,the margin deforms to different degrees once the geological bodies enter the early subduction,exerting influence on the strain localization in the subsequent extension,leading to the lithospheric breakup at various locations and start timings.Our results are compatible with the characteristics of timing migration of breakup unconformity in the South China Sea margin,and alsooffer reference for the geodynamic studies in other passive margins.