Abstract. Deep seismic acquisitions and a new kinematic study recently highlighted the presence of continental crust in both the southern Mozambique's Coastal Plain (MCP) and further offshore in the North Natal Valley (NNV). Such findings falsify previous geodynamic scenarios based on the kinematic overlap between Antarctica and Africa plates, thus profoundly impacting our understanding East-Gondwana break-up. Using an updated position of Antarctica with respect to Africa this study reconsider the formation mechanism of East-African margins and most specifically of the Limpopo margin (LM). Coincident wide-angle and multi-channel seismic data acquired within the PAMELA project are processed to image the sedimentary and deep crustal structure along a profile that runs from the northeastern NNV to the Mozambique basin (MB) striking through the LM. This dataset is combined with companion deep seismic profiles and industrial onshore-offshore seismic lines to provide a robust scenario for the formation and evolution of the LM. Our P-wave velocity model consists of an upper sedimentary sequence of weakly compacted sediments including intrusions and lava flows in the NNV while contourites and mass transport deposits dominates the eastern edge of the LM. This sequence covers a thick acoustic basement that terminates as a prominent basement high just west of the contourites and mass transport deposits domain. The acoustic basement has a seismic facies and velocity signature typical of a volcano-sedimentary basin and appears widespread over our study area extending toward the eastern MCP and NNV. Based on industrial well logs that calibrate our tectono-stratigraphic analysis we constrain its age to be pre-Neocomian. We further infer that either strike-slip or trans-tensional deformation occurred at the basement high which sustained uplift up to the Neocomian. At depth, the crystalline basement and uppermost mantle velocity structures show a progressive eastward crustal thinning of continental crust along the edge of the MCP/NNV and up to the location of the basement high. On its eastern side, however, a corridor of anomalous crust depicts the velocity signature of a volcanic basement overlying lower continental crust. We infer that strike-slip rifting along the LM was accommodated at depth by ductile shearing responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave to the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level and a shallow marine environment dominated during this period. Only after break-up in the MB decoupling occurred between the MCP/NNV and the corridor allowing for the latter to subside and being covered by deep marine sediments. We provide new insights into the early evolution and formation of the LM that takes into account both kinematic and geological constraints. This scenario favors strike-slip rifting along the LM meaning that no changes in extensional direction occurred between the rifting and the opening of the MB.

中文翻译：

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东非林波波河边缘的地壳结构，沿着莫桑比克大陆沿海平原和北纳塔尔河谷的走滑裂谷式走廊

摘要。近来进行的深部地震采集和一项新的运动学研究突显了莫桑比克南部沿海平原（MCP）和北纳塔尔谷地（NNV）进一步海上均存在大陆壳。这些发现基于南极洲和非洲板块之间的运动学重叠，伪造了先前的地球动力学情景，从而深刻影响了我们对东冈瓦纳破裂的认识。使用南极洲相对于非洲的最新状况，本研究重新考虑了东非边缘，尤其是林波波边缘（LM）的形成机制。在PAMELA项目中采集的重合的多角度和多通道地震数据经过处理后，沿着从NNV东北部到贯穿LM的莫桑比克盆地（MB）的剖面成像沉积和深层地壳结构。该数据集与伴随的深部地震剖面和工业陆上-近海地震线相结合，为LM的形成和演化提供了可靠的方案。我们的纵波速度模型由NNV内的侵入和熔岩流等弱压实沉积物的上部沉积层序组成，而LM东部边缘则以轮廓石和传质沉积为主。该序列覆盖了一个厚厚的声学基底，该基底终止于轮廓岩和大量输运沉积物区域以西的突出基底。声学地下室具有典型的火山沉积盆地的地震相和速度特征，并且在我们的研究区域中广泛分布，一直延伸到东部MCP和NNV。根据校准我们的构造-地层分析的工业测井记录，我们将其年龄限制为新西科前。我们进一步推断，基底高处发生走滑变形或超张变形，持续向上隆升直至新科目。在深处，结晶基底和最高地幔速度结构显示出沿MCP / NNV的边缘直至基底高处的大陆壳逐渐向东地壳变薄。然而，在其东侧，异常地壳的走廊描绘了覆盖下部大陆壳的火山基底的速度特征。我们推断，沿LM的走滑裂谷是由于韧性剪切作用而在深处适应的，这导致了大陆壳的变薄和下地壳物质向海的流动。这个过程伴随着强烈的岩浆作用，形成了火山岩基底，并赋予了其独特的结构和混合的性质。在此期间，整个区域仍处于较高水平，海洋环境占主导地位。仅在MCP / NNV与走廊之间发生MB解耦后，走廊才能平息并被深海沉积物覆盖。我们在考虑运动学和地质约束的前提下，对LM的早期演变和形成提供了新的见解。这种情况有利于沿LM的走滑裂谷，这意味着在裂谷和MB的开口之间在延伸方向上没有发生变化。