A reappraisal of epeirogenic flexure axes in Southern Africa
A reappraisal of epeirogenic flexure axes in Southern Africa
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南部非洲陆生弯曲轴的重新评估
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发表时间：
1999
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影响因子：
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通讯作者：
A. Moore
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作者：
A. Moore
南部非洲的主要排水分水岭被解释为反映了次大陆与相关盆地的形成有关的陆生挠曲线条。分隔沿海和内陆水系的大悬崖标志着悬崖轴线的轨迹。它是由早白垩世裂谷侧向隆升引发的，与冈瓦那裂解有关。地球物理研究表明，随后的侵蚀，加上大陆架上的沉积，将导致这一挠曲逐渐向内陆迁移。奥兰治-瓦尔河水系与林波波和莫洛波-诺西布-奥奥布流域之间的分水岭被指定为埃托沙-格里夸兰-德兰士瓦(EGT)轴。上白垩统沿着这个地轴挠曲，打乱了旧的排水线，开始了卡拉哈里组的沉积。白垩纪末期的奥文博兰-卡拉哈里-津巴布韦(OKZ)轴形成了津巴布韦赞比西河和林波波河之间的分水岭，并将后者与卡拉哈里的化石内生排水线分开，后者最初流入马克加迪亚迪平原系统。在博茨瓦纳南部，这条轴线由卡拉哈里-施韦勒水系界定，它将化石卡拉哈里水系与莫洛波-诺西布河水系分开。负责启动EGT和OKZ弯曲的过程知之甚少。然而，这两个轴和Escapment轴的推断年龄都与南部非洲的碱性火山活动相对应。这证明了大陆挠曲和火山活动之间存在联系。上新世的重大隆升发生在国家东部(西斯凯-斯威士兰轴线)大起伏和现在海岸线之间的一条中线上。沿穿越南非内陆的西南-东北轴线(指定为布什曼兰-哈茨轴线)弯曲的更柔和的上更新世是布什曼兰和奥兰治自由州形成主要平底壳(底板)的原因。有许多附属的隆起线(霍马斯、奥塔维和祖特潘斯伯格轴)与布什曼兰-哈茨轴平行。它们可能与相同的应力场有关，因此可能具有相似的年龄。后一条轴线都与博茨瓦纳北部的活动断裂次平行，这些断裂被解释为反映了东非裂谷系统沿着构造薄弱线向西南迁移。已确定的沿轴线的连续隆升为解释次大陆上的水系和剥蚀面的演化提供了一个框架。
Major drainage divides in southern Africa are interpreted to reflect lines of epeirogenic flexuring of the subcontinent associated with the formation of co-related basins. The Great Escarpment, which separates coastal and inland drainage systems, marks the locus of the Escarpment axis. It was initiated by Early Cretaceous rift flank uplift associated with the break-up Gondwana. Geophysical studies suggest that subsequent erosion, coupled with sedimentation on the continental shelf, would have resulted in progressive inland migration of this flexure. The divide between the Orange-Vaal River system and the Limpopo and Molopo-Nossib-Auob drainage basins is designated the Etosha-Griqualand-Transvaal (EGT) axis. Upper Cretaceous flexuring along this axis disrupted old drainage lines, and initiated deposition of the Kalahari formation. The end-Cretaceous Ovamboland-Kalahari-Zimbabwe (OKZ) axis forms the watershed between the Zambezi and Limpopo Rivers in Zimbabwe, and separates the latter river system from fossil endoreic drainage lines in the Kalahari, which originally emptied into the Makgadigadi Pans system. In the south of Botswana, this axis is defined by the Kalahari Schwelle, which separates the fossil Kalahari drainages from the Molopo-Nossib River system. Processes responsible for initiating the EGT and OKZ flexures are poorly understood. However, the inferred ages of both these two axes and the Escarpment axis correspond with episodes of alkaline volcanism in southern Africa. This argues for a link between continental flexuring and volcanic activity. Major Pliocene uplift occurred along a line intermediate between the Great Escarpment and the present coastline in the east of the country (the Ciskei-Swaziland axis). More subdued Plio-Pleistocene flexuring along a southwest-northeast axis (designated the Bushmanland-Harts axis) traversing the interior of South Africa was responsible for the formation of major pans ("floors") in Bushmanland and the Orange Free State. There are a number of subordinate lines of uplift (the Khomas, Otavi, and Zoutpansberg axes) which are parallel to the Bushmanland-Harts axis. They are presumably related to the same stress field, and thus probably of similar age. These latter axes are all subparallel to active faults in northern Botswana which are interpreted to reflect southwestwards migration of the east African rift system, following lines of structural weakness. Sequential uplift along the axes which have been identified provides a framework for interpreting the evolution of drainages and erosion surfaces on the sub-continent.