Late Cretaceous to Early Cenozoic initiation of rifting of the Windhoek Graben, Namibia

IF 1.2 4区 地球科学 Q2 GEOLOGY
R. Waren, J. Cartwright, M. Daly, R. Swart
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Abstract

The Windhoek Graben is a north-south trending rift in central Namibia that forms a prominent topographic feature bisecting an area of plateau uplift. It occupies a potentially crucial role in the propagation of the Late Cenozoic Southwest African Rift system regarding a possible continuation to the west of the Eiseb Rift. It is an unusual example of intra-continental rifting because it has no significant sediment fill associated with the period of active rifting, and hence the timing of rift activity and its tectonic relevance has not hitherto been established. To constrain the age of the Windhoek Graben we examine its regional geomorphic context and its relationship to four sites of igneous activity in the central Namibian Highlands. Two of these consist of clusters of eroded phonolitic tholoid bodies that have yielded 40Ar/39Ar dates of 32 Ma and 52 Ma, respectively, that we use to bracket the age of formation of a prominent remnant land surface, termed here the P52 Surface. From previous mapping of older intrusive igneous bodies, we argue that an even older land surface is partially preserved on the highest features in the area, and this surface (termed PRS) defines an initial domally uplifted surface from which initial drainage radiated, and onto which the earliest volcanic products associated with the Graben were erupted. In particular, the strong similarity in dyke and fault orientations is used to argue for a causal connection between the earliest magmatic activity and the onset of rifting. Long range correlation of PRS into the adjacent Aranos Basin strongly suggests a Late Cretaceous age for this earliest magmatic activity and the onset of rifting, but we cannot exclude a younger origin, any time up to the Early Eocene.
纳米比亚温得和克地堑晚白垩世至早新生代的起裂作用
温得和克地堑是纳米比亚中部一个南北走向的裂谷,形成了一个突出的地形特征,将高原隆起地区一分为二。它在晚新生代西南非洲裂谷系统的传播中扮演着潜在的关键角色,可能延续到艾塞布裂谷的西部。这是一个不寻常的大陆内裂谷作用的例子,因为它没有与活跃裂谷作用时期相关的重要沉积物填充,因此裂谷活动的时间及其构造相关性迄今尚未确定。为了限制温得和克地堑的年龄,我们研究了它的区域地貌背景及其与纳米比亚中部高地四个火成岩活动地点的关系。其中两个由侵蚀的声母岩类体组成,它们分别产生了32 Ma和52 Ma的40Ar/39Ar年代,我们用它来表示一个突出的残余地表的形成年龄,这里称为P52地表。从之前对更古老的侵入火成岩的制图中,我们认为在该地区的最高特征上部分保留了一个更古老的陆地表面,这个表面(称为PRS)定义了一个最初的穹窿隆起表面,从这个表面上辐射出最初的排水,并在这个表面上爆发了与地堑相关的最早的火山产物。特别是,岩脉和断层方向的强烈相似性被用来论证最早的岩浆活动与裂陷的发生之间的因果关系。与邻近的Aranos盆地的PRS的长期对比强烈表明,最早的岩浆活动和裂谷的开始时间为晚白垩世,但我们不能排除一个更年轻的起源,任何时候都可以追溯到早始新世。
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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