Despite significant study, when and how plate tectonics initiated on Earth remains contentious. Geologic evidence from some of Earth's earliest cratons has been interpreted as reflecting the formation of initial continental blocks by non-subduction processes, which then trigger subduction initiation at their margins. Numerical models of mantle convection with a plastic yield stress rheology have shown this scenario is plausible. However, whether continents can trigger subduction initiation has not been tested with other rheologies. We, therefore, use numerical models of mantle convection with an imposed continental block to test whether continents facilitate subduction initiation with a grain-damage mechanism, where weak shear zones form by grain size reduction. Our results show that continents modestly enhance stresses in the lithosphere, but not enough to significantly impact lithospheric damage or subduction initiation: continents have minimal influence on lithospheric damage or plate speed, nor does subduction preferentially initiate at the continental margin. A new regime diagram that includes continental blocks shows only a small shift in the boundary between the mobile-lid and stagnant-lid regimes when continents are added. However, as we do find that stresses are modestly enhanced at the continental margin in our models, we develop a scaling law for this stress enhancement to more fully test whether continents could trigger subduction initiation on early Earth. We find that lithospheric stresses supplied by continents are not sufficient to initiate subduction on the early Earth on their own with grain-damage rheology; instead, additional factors would be required.

中文翻译：

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大陆对颗粒损伤对流俯冲引发的有限影响


尽管进行了大量研究，但板块构造何时以及如何在地球上开始仍然存在争议。来自地球上一些最早的克拉通的地质证据被解释为反映了非俯冲过程形成的初始大陆块，然后在其边缘触发俯冲起始。具有塑性屈服应力流变学的地幔对流数值模型表明这种情况是合理的。然而，大陆是否可以引发俯冲起始尚未用其他流变学进行过测试。因此，我们使用强加大陆块的地幔对流数值模型来测试大陆是否通过颗粒损伤机制促进俯冲起始，其中通过颗粒尺寸减小形成弱剪切带。我们的结果表明，大陆适度增强了岩石圈中的应力，但不足以显着影响岩石圈损伤或俯冲起始：大陆对岩石圈损伤或板块速度的影响很小，俯冲也不会优先在大陆边缘起始。包含大陆块的新体系图显示，当添加大陆时，移动盖和静止盖体系之间的边界仅发生很小的变化。然而，正如我们确实发现在我们的模型中大陆边缘的应力适度增强一样，我们为这种应力增强制定了比例定律，以更全面地测试大陆是否可以触发早期地球的俯冲起始。我们发现，大陆提供的岩石圈应力不足以通过颗粒损伤流变学本身引发早期地球的俯冲；相反，需要额外的因素。