Hierarchical segmentation of the Malawi Rift: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental rifts
Hierarchical segmentation of the Malawi Rift: The influence of inherited lithospheric heterogeneity and kinematics in the evolution of continental rifts
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DOI：
10.1002/2015tc003953
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发表时间：
2015-12-01
期刊：
影响因子：
4.2
通讯作者：
Atekwana, Estella A.
中科院分区：
文献类型：
--
作者：
Lao-Davila, Daniel A.;Al-Salmi, Haifa S.;Atekwana, Estella A.
我们利用对航天飞机雷达地形测绘任务数字高程模型的详细分析以及航空磁测数据的观测结果，来研究继承性岩石圈非均质性和运动学在基本无岩浆活动的大陆裂谷分段中的影响。我们聚焦于新生代马拉维裂谷，它是东非裂谷系西支的南延部分。这条北东走向的裂谷穿过不同走向的前寒武纪以及古生代 - 中生代构造。我们发现该裂谷可分级划分为一级和二级分段。在一级分段中，我们将裂谷分为北段、中段和南段。在北段，裂谷沿古元古代和新元古代地形分布，其构造纹理有利于在发育良好的边界断层内发生伸展作用。中段位于中元古代 - 新元古代地形内，区域构造与裂谷延伸方向斜交。我们认为，由于缺乏有利于伸展定位的继承性岩石圈非均质性，导致该段裂谷发育为边界断层不发育的浅地堑。在南段，中元古代 - 新元古代岩石被重新激活并发育出边界断层。在二级分段中（仅在北段观察到），我们将该段分为五个分段，近似于四个具有交替极性的半地堑/不对称地堑。极性的变化与在约150千米长的交替边界断层段相关的重叠区内出现的翻转式完整地堑相吻合。在马拉维裂谷因伸展而张开的过程中，继承性岩石圈非均质性在促进其分段方面起到了主要作用。
We used detailed analysis of Shuttle Radar Topography Mission-digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental rifts. We focused on the Cenozoic Malawi Rift, which represents the southern extension of the Western Branch of the East African Rift System. This north trending rift traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the rift can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the rift into Northern, Central, and Southern sections. In its Northern Section, the rift follows Paleoproterozoic and Neoproterozoic terrains with structural grain that favored the localization of extension within well-developed border faults. The Central Section occurs within Mesoproterozoic-Neoproterozoic terrain with regional structures oblique to the rift extent. We propose that the lack of inherited lithospheric heterogeneity favoring extension localization resulted in the development of the rift in this section as a shallow graben with undeveloped border faults. In the Southern Section, Mesoproterozoic-Neoproterozoic rocks were reactivated and developed the border faults. In the second-order segmentation, only observed in the Northern Section, we divided the section into five segments that approximate four half-grabens/asymmetrical grabens with alternating polarities. The change of polarity coincides with flip-over full-grabens occurring within overlap zones associated with similar to 150 km long alternating border faults segments. The inherited lithospheric heterogeneity played the major role in facilitating the segmentation of the Malawi Rift during its opening resulting from extension.