Abstract It is widely accepted that subduction initiation at modern Earth passive margin systems critically depends on the buoyancy and strength of the oceanic lithosphere and requires failure of the load-bearing crustal and mantle layers. As such, subduction initiation upon orthogonal convergence is controlled by the age of the oceanic lithosphere and thus the strength contrast at the margin. However, it is still unclear where along the margin and how subduction initiates. In particular, rheologically-controlled mechanisms are poorly understood and require further investigation. Therefore, this combined analogue and numerical modelling study aims at exploring the effects of first order rheological and kinematic conditions on subduction initiation at passive margins. Our results highlight the sensitivity of early stages of subduction initiation to the initial rheological setup as well as evolving thermo-mechanical feedback mechanisms. Additionally, they provide more insights on the conditions responsible for the locus of subduction initiation. We infer that the locus of subduction is controlled by the rheology of both the crust and the mantle lithosphere at the margin, which is in strong correlation with the thermal age of the oceanic lithosphere. Suitable conditions for subduction initiation at passive margins correspond to an intermediate age (ca. 80 Myr) of the oceanic lithosphere. In all other cases deformation localizes within the oceanic lithosphere or affects the entire continent. We advocate the significance of crust-mantle decoupling at the passive margin for its inversion and possible evolution towards a subduction zone. Additionally, the development of a self-sustaining subduction zone will fail in the absence of weakening mechanisms taking place in the mantle lithosphere such as thermal softening (shear heating) and low temperature plasticity (Peierls mechanism).

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被动边缘俯冲开始的应变定位机制

摘要 人们普遍认为，现代地球被动边缘系统的俯冲开始主要取决于海洋岩石圈的浮力和强度，并且需要承载地壳和地幔层的破坏。因此，正交收敛时的俯冲开始受大洋岩石圈年龄和边缘强度对比控制。然而，目前尚不清楚沿边缘的位置以及俯冲是如何开始的。特别是，对流变控制的机制知之甚少，需要进一步研究。因此，这种结合模拟和数值模拟的研究旨在探索一阶流变学和运动学条件对被动边缘俯冲开始的影响。我们的结果强调了俯冲开始的早期阶段对初始流变学设置以及不断发展的热机械反馈机制的敏感性。此外，他们提供了更多关于导致俯冲起始位置的条件的见解。我们推断俯冲轨迹受边缘地壳和地幔岩石圈流变控制，这与大洋岩石圈的热年龄有很强的相关性。在被动边缘开始俯冲的合适条件对应于大洋岩石圈的中间年龄（约 80 Myr）。在所有其他情况下，变形集中在海洋岩石圈内或影响整个大陆。我们主张被动边缘的壳幔解耦对其反转和可能向俯冲带演化的重要性。此外，如果地幔岩石圈中不存在热软化（剪切加热）和低温塑性（Peierls 机制）等弱化机制，自持俯冲带的发展将失败。