DYNAMIC MECHANISM OF RIFT SYSTEMS IN WEST AND CENTRAL AFRICA
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摘要: 中西非裂谷系是沿中非剪切带及邻区发育的一系列中新生代裂谷盆地，其成因机理一直存在争议。中西非裂谷系的构造演化主要经历了三个演化阶段，其中在早白垩世进入强烈断陷期，是盆地形成的重要阶段。以早白垩世中西非裂谷系的地质背景为基础，运用弹性力学有限元数值模拟方法，通过应力场和应变场的分析，为中西非裂谷系形成的力学机制提供依据。模拟结果表明，早白垩世非洲大陆内部走滑和伸展作用并存，中非剪切带不是所谓的"转换断层"，而是与中西非裂谷系同时形成和发育的构造。中西非裂谷系是在中新生代泛大陆裂解时期，非洲板块绕西北非地块逆时针旋转，非洲内部不同地块在统一构造应力场作用下，由于伸展和走滑的差异作用形成和发育的。Abstract: The rift systems in West and Central Africa that developed along the shear zone in Central Africa is a series of Mesozoic-Cenozoic rift basins, and their formation mechanism is still a matter of debate. The evolution of those rift systems has three stages, and Early Cretaceous is the most important one for the basin formation, in which the rifts and major fault zones were strongly active. Based on the geological setting of rift systems in West and Central Africa in Early Cretaceous, using linear elastic theory with two dimensional finite element numerical simulation, through the analysis of the stress field and the strain field, reliable evidence to the mechanical mechanism of rift systems are produced. The simulation results suggest that strike-slipping and extensional process coexist in African continent in Early Cetaceous, and the shear zone in Central Africa is not a "transform fault" but a structure that formed and developed simultaneously with the rift systems in West and Central Africa. In Mesozoic-Cenozoic Pangea disintegration period, due to the different motion rates of the three blocks along parallel slip vectors under the unified tectonic stress field and the counterclockwise rotation around WB by African plate, rift systems were formed and developed.
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图 1 非洲北部裂谷分布图[2]
WB—西北非地块；ANB—东北非地块；AB—中南非地块；CASZ—中非剪切带
Figure 1. Distribution map of the rifts in North Africa
图 2 早白垩世泛大陆裂解时期非洲裂谷系分布图[15]
WB—西北非地块；ANB—东北非地块；SB—中南非地块
Figure 2. Distribution of the rife systems in Africa in Early Cetaceous Pangea distintegration period
图 3 早白垩世数值模拟力学模型图(灰色区为活动带)
WB—西北非地块；ANB—东北非地块；SB—中南非地块
Figure 3. Mechanical model of the numerical simulation in the Early Cetaceous
图 4 早白垩世非洲大陆的张应变等值线图
WB—西北非地块；ANB—东北非地块；SB—中南非地块
Figure 4. Contour map of tensile strain in the Early Cretaceous African continent
图 5 非洲裂谷系白垩纪伸展量或滑移量图[14]
WB—西北非地块；ANB—东北非地块；SB—中南非地块
Figure 5. Extension and slip map of African rift systems in Cretaceous
图 6 早白垩世非洲大陆的最小主压应力方向图
WB—西北非地块；ANB—东北非地块；SB—中南非地块
Figure 6. The minimum principal compressive stress (σHmim) trajectory map of the African continent in Early Cretaceous
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