Abstract The Afar region in East Africa is a key locality for studying continental break-up. Within Afar, passive margins are developing, of which the Southern Afar Margin (SAM) contains synthetic (basinward) faulting, whereas crustal flexure, antithetic faulting and marginal grabens occur along the Western Afar Margin (WAM). Numerous conflicting scenarios for the evolution of the WAM exist. In this analogue modelling study we test various factors that may affect the development of a WAM-style passive margin: brittle crustal thickness, (en echelon) rheological contrasts, sedimentation and oblique extension. Our experimental results illustrate how marginal flexure due to a weak lower crust below Afar can elegantly account for the structural features of the WAM. Brittle crustal thickness controls what structures occur: a thinner brittle crust accommodates flexure internally, whereas increasing brittle thicknesses lead to faulting. Large escarpment faults develop early on, followed by late-stage antithetic faulting and marginal grabens. A thicker brittle crust also causes enhanced subsidence, and increased strength contrasts between lower crustal domains leads to more localized deformation. Basin-wide sedimentation causes enhanced subsidence, as well as longer activity along large synthetic (escarpment) faults. Finally, oblique extension clearly prevents the development of marginal grabens, which only form in near-orthogonal extension. These results support a tectonic scenario involving initial oblique extension due to Arabian plate motion, creating echelon synthetic escarpment faults along the WAM. After the Danakil Block started its independent rotation, near-orthogonal extension conditions were established, allowing (enhanced) marginal flexure, antithetic faulting and marginal graben formation along the older en echelon escarpment. Differences in extension obliquity may also explain the differences in structural architectures between the WAM and SAM. The characteristics of the WAM are typical of magma-rich passive margins, and the margin has great potential for studying continental break-up and (magma-rich) passive margin formation.

中文翻译：

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东非阿法尔边缘弯曲的模拟建模：对被动边缘形成的影响

摘要 东非阿法尔地区是大陆分裂研究的重点地区。在阿法尔内，被动边缘正在发育，其中阿法尔南缘（SAM）包含合成（向盆地）断层，而地壳弯曲、对置断层和边缘地堑沿阿法尔西缘（WAM）出现。WAM 的演变存在许多相互矛盾的场景。在这项模拟建模研究中，我们测试了可能影响 WAM 式被动边缘发展的各种因素：脆性地壳厚度、（梯形）流变对比、沉积和倾斜延伸。我们的实验结果表明，由于阿法尔下方的弱下地壳造成的边缘弯曲如何巧妙地解释了 WAM 的结构特征。脆性地壳厚度控制发生的结构：较薄的脆性外壳在内部容纳弯曲，而增加脆性厚度会导致断层。大的悬崖断层早期发育，其次是晚期对位断层和边缘地堑。较厚的脆性地壳也会导致下沉加剧，而下地壳域之间强度差异的增加导致更多的局部变形。整个盆地的沉积作用会导致下沉加剧，以及沿着大型合成（悬崖）断层活动时间更长。最后，倾斜延伸明显阻止了边缘地堑的发展，边缘地堑仅在接近正交的延伸中形成。这些结果支持了一种由于阿拉伯板块运动而导致的初始倾斜延伸的构造情景，沿着 WAM 形成了梯形合成悬崖断层。Danakil Block开始独立旋转后，建立了接近正交的延伸条件，允许（增强的）边缘弯曲、对立断层和沿较旧梯形悬崖的边缘地堑形成。延伸倾斜度的差异也可以解释 WAM 和 SAM 之间结构架构的差异。WAM的特征是富岩浆被动边缘的典型特征，该边缘具有研究大陆破裂和（富岩浆）被动边缘形成的巨大潜力。