By taking advantage of the recent availability of a broadband seismic data set from Networks NR and BX covering the entire country of Botswana, we conduct a systematic receiver function investigation of the topography of the 410 and 660 km discontinuities beneath the incipient Okavango rift zone (ORZ) in northern Botswana and its adjacent Archean‐Proterozoic tectonic provinces in southern Africa. Similar to a previous mantle transition zone (MTZ) discontinuity study using data from a 1‐D profile traversing the ORZ, a normal MTZ thickness is observed in most parts of the study area. This is inconsistent with the existence of widespread positive thermal anomalies in the MTZ and further implies that active thermal upwelling from the lower mantle plays an insignificant role in the initiation of continental rifting. The results also suggest that cold temperature presumably associated with thick cratonic keels has indiscernible influence on the thermal structure of the MTZ. The expanded data set reveals several isolated areas of slight (~10 km or smaller) MTZ thinning. The largest of such areas has a NE‐SW elongated shape and is mostly caused by relative deepening of the 410 km discontinuity rather than shallowing of the 660 km discontinuity. These characteristics are different from those expected for a typical mantle plume. We speculate that the thinner‐than‐normal MTZ may be induced by minor thermal upwelling associated with late Mesozoic‐early Cenozoic lithospheric delamination, a recently proposed mechanism that might be responsible for the high elevation of southern Africa.

中文翻译：

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新生代奥卡万戈裂谷带和相邻前寒武纪省之间410和660 km间断点的地形

利用最近从覆盖整个博茨瓦纳国家的NR和BX网络获得的宽带地震数据集的优势，我们对初始Okakago裂谷带（ORZ）下方410和660 km不连续点的地形进行了系统的接收器功能调查。 ）位于博茨瓦纳北部及其南部非洲邻近的太古宙—元古代构造省份。与以前的地幔过渡带（MTZ）不连续性研究类似，该研究使用的是穿过ORZ的一维剖面数据，在研究区域的大部分地区都观察到了正常的MTZ厚度。这与MTZ中广泛存在的正热异常是不一致的，并且进一步暗示着来自下地幔的活跃热上升在大陆裂谷的引发中起着微不足道的作用。结果还表明，大概与克拉通厚龙骨有关的低温对MTZ的热结构没有明显的影响。扩展后的数据集显示出一些孤立的区域，这些区域的MTZ细化程度较小（约10 km或更小）。这些区域中最大的区域是NE-SW拉长的形状，主要是由410 km不连续性的相对加深而不是660 km不连续性的变浅引起的。这些特征与典型的地幔柱预期的特征不同。我们推测，比正常水平更薄的MTZ可能是由与中生代晚期早新生代岩石圈剥落有关的较小的热上升引起的，这是最近提出的可能与南部非洲高海拔有关的机制。