Abstract We used high-resolution (500 × 250 m) two-dimensional lithospheric-scale thermo-mechanical numerical modeling to unravel the unexpected topographic and thermal evolutions recorded during the necking phase of several rift systems worldwide. Through a systematic analysis we studied how the lithosphere rheology impacts the topographic and thermal evolutions across the entire width of magma-poor and sediment-starved rift systems until their crust is locally thinned to 10 km. We quantified the evolution of topography, uplift and subsidence rates, accommodation and emerged space creation, temperature and surface heat flow for a wide panel of crustal and mantle rheologies to provide an overview of possible rifting behaviors. Extension of a lithosphere for which the crust and mantle are mechanically decoupled by a weak lower crust generates complex morphotectonic evolutions, with the formation of temporarily restricted sub-basins framed by uplifted parts of the future distal margin. Mechanical decoupling between the crust and mantle controls also largely the thermal evolution of rift systems during the necking phase since, for equivalent extension rates and initial geotherms: (i) weak/decoupled lithospheres have a higher geothermal gradient at the end of the necking phase than strong/coupled lithospheres; and (ii) weak/decoupled lithospheres show intense heating of the lower crust at the rift center and intense cooling of the crust on either side of the rift center, unlike strong/coupled lithospheres. These behaviors contrast with the continuous subsidence and cooling predicted by the commonly used depth-uniform thinning model. Accommodation space in the evolving basins is first generated by vertical crustal velocities and subsequently by horizontal velocities causing the widening of the earlier formed basin. Processes such as strain softening and mantle fertilization have a limited impact on the primary morphology and thermal state of rift systems before the crust is thinned to 10 km but may locally amplify relief and thermal heterogeneities.

中文翻译：

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壳幔机械耦合对“贫岩”和“缺乏沉积物”裂谷系统颈缩阶段地貌和热演化的影响：数值模拟研究

摘要 我们使用高分辨率 (500 × 250 m) 二维岩石圈尺度热机械数值模拟来揭示在全球几个裂谷系统颈缩阶段记录的意外地形和热演化。通过系统分析，我们研究了岩石圈流变学如何影响岩浆贫乏和沉积物匮乏的裂谷系统整个宽度的地形和热演化，直到它们的地壳局部变薄到 10 公里。我们量化了大量地壳和地幔流变学的地形、隆起和沉降速率、适应和出现的空间创造、温度和地表热流的演变，以提供可能的裂谷行为的概述。地壳和地幔被弱的下地壳机械解耦的岩石圈的延伸产生了复杂的形态构造演化，形成了由未来远端边缘的隆起部分构成的暂时受限的亚盆地。地壳和地幔之间的机械解耦也很大程度上控制了颈缩阶段裂谷系统的热演化，因为对于等效的伸展率和初始地温：(i) 弱/解耦岩石圈在颈缩阶段末具有更高的地温梯度强/耦合岩石圈；(ii) 弱/解耦岩石圈显示裂谷中心下地壳强烈加热，裂谷中心两侧地壳强烈冷却，这与强/耦合岩石圈不同。这些行为与常用深度均匀减薄模型预测的连续下沉和冷却形成对比。演化盆地中的容纳空间首先由垂直地壳速度产生，随后由水平速度产生，导致早期形成的盆地扩大。在地壳减薄到 10 公里之前，应变软化和地幔肥化等过程对裂谷系统的主要形态和热状态的影响有限，但可能会局部放大地壳和热非均质性。