Geology of the Malawi Rift: kinematic and tectonosedimentary background to the Chiwondo Beds, northern Malawi
Geology of the Malawi Rift: kinematic and tectonosedimentary background to the Chiwondo Beds, northern Malawi
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马拉维裂谷地质：马拉维北部 Chiwondo 层的运动学和构造沉积背景
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发表时间：
1995
期刊：
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通讯作者：
C. Betzler
中科院分区：
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作者：
U. Ring;C. Betzler
摘要新近纪和第四纪断裂的运动学分析表明，马拉维裂谷的伸展方向由东北偏东向东南旋转。裂谷发育开始于约8.6 Ma，正断层导致中生代沉积物的侵蚀和再沉积，并形成以西北、北和东北走向的正断层为界的半地堑。持续的正断层作用导致断块断层作用和盆地沉降，形成河流系统，最终形成裂谷湖（古马拉维湖）。根据陆上沉积记录，初步认为湖相沉积的年龄为4.5 ~ 4.0Ma。这一阶段的正断层主要负责今天的马拉维湖盆地形态。断层运动学和沉积模式的重大变化是由于主伸展轴和缩短轴的旋转，可能发生在0.2 Ma之间。因此，从第一个裂谷阶段继承的结构模式不再适合于适应伸展变形和走滑断层变得更加重要。走滑体制可能造成了湖泊沉积物和裂谷内基底脊的隆起和侵蚀，以及局部平移挤压区域内沿裂谷侧翼的沿着隆起和侵蚀，但也由于平移张裂而形成了局部沉积盆地。主要显示第一变形增量的较老断层仅限于裂谷的最外侧。向中心，断层描绘了增加的运动的走滑分量，这表明变形传播向裂谷中心，这导致在一个缩小的活动裂谷环境随着时间的推移。
Abstract Kinematic analysis of Neogene and Quaternary faults demonstrates that the direction of extension in the Malawi Rift rotated from east-northeast to southeast. Rift development commenced at about 8·6 Ma with normal faulting causing erosion and re-sedimentation of Mesozoic deposits and formation of half-grabens bounded by northwest-, north-, and northeast-striking normal faults. Continued normal faulting led to block faulting and basin subsidence which created a riverine system and eventually formed a rift lake (Palaeo-Lake Malawi). Based on the onshore sedimentary record an age of 4·5 to 4·0 Ma appears likely for initial lacustrine sedimentation. This phase of normal faulting is largely responsible for the present-day basin morphology of Lake Malawi. A major change in fault kinematics and also in the sedimentation pattern occurred due to rotation of the principal extension and shortening axes, probably between 0·2 Ma. As a result, the structural pattern inherited from the first rifting phase was no longer suitably oriented to accommodate extensional deformation and strike-slip faulting became more important. The strike-slip regime may have caused uplift and erosion of the lake sediments and of basement ridges within the rift and along the rift flanks in regions of local transpression, but also created local sedimentary basins due to transtension. Older faults that show mainly the first deformation increment are restricted to the outermost parts of the rift. Toward the center, the faults depict an increase in strike slip components of movement, suggesting deformation propagation toward the rift center, which results in a narrowing of the active rift environments with time.