Abstract The Stavelot-Venn Massif (SVM) is the major Cambrian-Ordovician inlier of the Ardenne Allochthon (Southern Belgium). The SVM belongs to the Avalonian microcontinent and was affected by the Caledonian and Variscan orogenies. The Ardenne Allochthon constitutes the northwestern part of the Rheno-Hercynian domain, just south of the Variscan northern front. By contrast, the comparable Avalonian Cambro-Silurian Brabant Massif (northern Belgium) is located just to the north of this front and is not affected by the Variscan orogeny. In this study, we compiled the SVM available but dispersed data concerning the the Cambrian-Ordovician series (field, geochemistry, isotopes). In addition, we acquired new data especially LA-ICP-MS detrital and magmatic zircon ages and Nd isotopes. The comparison with the Brabant Massif, which also belongs to Avalonia and whose geological history is well known, is particurlarly enlightening. SVM Cambrian and lowermost Ordovician depositional environments are similar to the Brabant Massif but sediment thickness is significantly lower (2000 m vs 9000 m). During the remaining Ordovician and Silurian, after the opening of the Rheic Ocean, Brabant and SVM behaved differently, pointing to the existence of two different basements, whereby the basement underneath the SVM acted more rigidly (metacratonic). The SVM environment matches a rift shoulder while the Brabant was located in the rift itself. Our comprehensive study of detrital zircon ages from Cambrian-Ordovician sediments establishes the relative contributions over time of three composite sources: the West African craton, the Western Amazonian craton and the Pan-African orogen. This allowed us to determine a fine record of the tectonic events, distant or local, at the origin of the supply variations from these major sources. The detrital zircon age pattern of the Pridoli conglomerate (Ardennian unconformity) deposited after a sedimentation hiatus of 45 Myrs, is very distinctive. It shows a continuous record between 467 Ma and 420 Ma (97% zircons) that we relate to the activity of a large igneous province (LIP). The latter would be located along the south-eastern boundary of Avalonia, denying the existence of a Silurian island arc as previously proposed. The geochemical evidence indicates that most magmatic rocks have a crustal origin in relation to melting in an intracontinental setting due to stress applied at the Avalonia plate margin. Finally, we propose a geodynamic model in which the rigid basement of the Rheno-Hercynian domain originated from the tearing of a metacratonic fragment of the West African craton, which left a large scar on its western margin (Mauritania/Senegal). This metacratonic fragment includes only the Silurian Brabant western foreland and extends to England, including the Midlands microcraton.

中文翻译：

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Stavelot-Venn 地块（比利时阿登），一个从西非克拉通剥离的裂陷台肩盆地：制图学、地层学、沉积学、锆石年龄的新 U-Pb、地球化学和 Nd 同位素证据

摘要 Stavelot-Venn Massif (SVM) 是Ardenne Allochthon（比利时南部）的主要寒武纪-奥陶纪内层。SVM 属于阿瓦隆微大陆，受到加里东和瓦里斯坎造山运动的影响。Ardenne Allochthon 构成了 Rheno-Hercynian 域的西北部，就在 Variscan 北锋以南。相比之下，可比较的阿瓦隆纪坎布罗-志留纪布拉班特地块（比利时北部）就位于这条锋线的北部，不受瓦里斯坎造山运动的影响。在这项研究中，我们汇编了有关寒武纪-奥陶纪系列（场、地球化学、同位素）的 SVM 可用但分散的数据。此外，我们还获得了新数据，尤其是 LA-ICP-MS 碎屑和岩浆锆石年龄和 Nd 同位素。与布拉班特地块的比较，这也属于阿瓦隆尼亚，其地质历史众所周知，特别具有启发性。SVM 寒武纪和最低奥陶纪沉积环境与布拉班特地块相似，但沉积物厚度明显较低（2000 米对 9000 米）。在剩余的奥陶纪和志留纪期间，莱茵洋开放后，布拉班特和 SVM 表现不同，指出存在两个不同的基底，其中 SVM 下方的基底表现得更加僵硬（metacratonic）。SVM 环境与裂谷肩相匹配，而 Brabant 位于裂谷本身。我们对寒武纪-奥陶纪沉积物碎屑锆石年龄的综合研究确定了三个复合来源随时间的相对贡献：西非克拉通、西亚马逊克拉通和泛非造山带。这使我们能够在这些主要来源的供应变化的起源处确定远距离或局部构造事件的精细记录。在 45 Myrs 的沉积中断后沉积的 Pridoli 砾岩（亚登不整合面）的碎屑锆石年龄模式非常独特。它显示了 467 Ma 和 420 Ma（97% 锆石）之间的连续记录，我们与一个大型火成岩省 (LIP) 的活动有关。后者将位于阿瓦隆尼亚东南边界，否认先前提出的志留纪岛弧的存在。地球化学证据表明，由于施加在阿瓦隆尼亚板块边缘的应力，大多数岩浆岩在陆内环境中的熔化过程中具有地壳起源。最后，我们提出了一个地球动力学模型，其中 Rheno-Hercynian 域的刚性基底起源于西非克拉通的一个元克拉通碎片的撕裂，它在其西部边缘（毛里塔尼亚/塞内加尔）留下了一个大疤痕。这个元克拉通碎片仅包括志留纪布拉班特西部前陆，并延伸至英格兰，包括米德兰兹微克拉通。