从南大西洋裂解过程解密大陆漂移的驱动力

Decipher the driving force in continental drift from new insights about the South Atlantic breakup process

南大西洋裂解造成的非洲和南美洲的大陆分离得到了广泛认可,该区域也与大陆漂移学说的诞生密切相关。但大陆漂移的驱动力从其提出至今一直存在争议,定量化分析大西洋裂解过程中板块运动的驱动力显得尤为重要。我们研究了南大西洋两侧被动大陆边缘盆地区域的两条深反射地震勘探剖面,在构造地 质解译基础上,详细估算了非洲大陆的莫霍面倾角,得到了沿莫霍面地壳重力滑移剪切力的大小,用于解释 大西洋裂解过程中非洲大陆运动的动力机制。结果说明,非洲大陆板块在地幔上涌形成的倾斜界面上能够 产生强大的重力滑移力,且南部驱动力大于中部。大陆板块依靠连续的地幔热上涌和重力滑移力会持续漂 移。该模型能够合理解释大西洋上诸多线状分布的大陆残片的成因机制,也能合理解释南大西洋南部宽度 大于中部的内在原因,最后对南大西洋的打开过程进行了精细的构造演化史恢复。该研究为板块运动提供 了一个新的动力模式,为认识板块运动驱动力提供了更为精确的约束信息。

It has been widely recognized that the separation of the African and South American continents is caused by the South Atlantic breakup.The South Atlantic region is highly relevant to the development of the continental drift hypothesis.The driving force behind continental drift,however,has been in debate ever since the hypothesis was proposed.Therefore,quantitative analysis of the forces driving plate movement in the process of Atlantic breakup is particularly important.Here,we analyzed two deep seismic reflection survey profiles located on either side of the South Atlantic,in passive continental margin basins,and estimated the Moho dip angle of the African continent on the basis of tectonic geological interpretation.We then calculated the magnitude of crustal gravitational slip shear force along the Moho to explain the dynamic mechanism of African continent movement in the process of Atlantic breakup.We demonstrated that the African continental crust can produce a strong gravitational slip force on the inclined interface formed by mantle upwelling,and the shear force is greater in the south than in the middle part of the crust.According to our analysis,the continental crust can drift continuously by continuous hot mantle upwelling and gravitational slide.This model can reasonably explain the genetic mechanism for the many linear continental fragments in the Atlantic Ocean,and it can also provide an internal reason for why the South Atlantic today is wider in the south than it is in the middle.Based on this model we reconstructed the tectonic evolutionary history of the South Atlantic breakup process.This research established a new dynamic model of plate motion and provided more accurate constraint on understanding the driving force behind plate movement.