Reconciling lithospheric rheology between laboratory experiments, field observations and different tectonic settings
Reconciling lithospheric rheology between laboratory experiments, field observations and different tectonic settings
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协调实验室实验、现场观测和不同构造环境之间的岩石圈流变学
DOI：
10.1093/gji/ggab382
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发表时间：
2021
影响因子：
2.8
通讯作者：
Watts, Anthony B
中科院分区：
文献类型：
--
作者：
Bellas, Ashley;Zhong, Shijie;Watts, Anthony B
最近的模拟研究表明，实验室衍生的流变学太强，无法再现在夏威夷群岛的挠曲观测，而同样的流变学似乎与环太平洋俯冲带的外隆起海沟挠曲一致。总的来说，这些结果表明，海洋板块边界的流变性强于其内部，如果正确的话，这对理解海沟的形成和俯冲的开始提出了挑战。为了理解这一困境，我们首先调查实验室推导的流变学使用全动态粘弹性加载模型，并发现它是太强了，以再现观测推断的弹性厚度，Te，在大多数板内部设置。然而，如果低温塑性的屈服应力显著降低，例如，通过从320 kJ mol−1降低活化能，则可以解释Tecan，如Mei等人，到190 kJ mol−1as的范围内，这意味着夏威夷下面的岩石圈没有异常。其次，我们测试的精度模拟方法来约束俯冲岩石圈的流变学，包括屈服应力包络（YSE）的方法，和破碎的弹性板模型（BEPM）。我们表明，YSE方法准确地再现了modelTeto的误差在10%以内，只有适度的敏感性，假设的应变率和曲率。最后，我们表明，一个连续板的响应显着增强时，自由边缘被引入或附近的边缘负载，如在BEPM，是敏感的粘性耦合的程度在自由边缘。由于俯冲岩石圈是连续的，并且通常与下沉板块机械耦合，因此BEPM可能会错误地引入一个弱点，从而由于权衡而高估了海沟。这可以解释最近的模拟研究结果，即俯冲洋板块的流变性比其内部更强。然而，为了量化这一点，未来将需要使用更先进的热和机械模型进行进一步研究。
Recent modelling studies have shown that laboratory-derived rheology is too strong to reproduce observations of flexure at the Hawaiian Islands, while the same rheology appears consistent with outer rise—trench flexure at circum-Pacific subduction zones. Collectively, these results indicate that the rheology of an oceanic plate boundary is stronger than that of its interior, which, if correct, presents a challenge to understanding the formation of trenches and subduction initiation. To understand this dilemma, we first investigate laboratory-derived rheology using fully dynamic viscoelastic loading models and find that it is too strong to reproduce the observationally inferred elastic thickness,Te, at most plate interior settings. TheTecan, however, be explained if the yield stress of low-temperature plasticity is significantly reduced, for example, by reducing the activation energy from 320 kJ mol−1, as in Meiet al., to 190 kJ mol−1as was required by previous studies of the Hawaiian Islands, implying that the lithosphere beneath Hawaii is not anomalous. Second, we test the accuracy of the modelling methods used to constrain the rheology of subducting lithosphere, including the yield stress envelope (YSE) method, and the broken elastic plate model (BEPM). We show the YSE method accurately reproduces the modelTeto within ∼10 per cent error with only modest sensitivity to the assumed strain rate and curvature. Finally, we show that the response of a continuous plate is significantly enhanced when a free edge is introduced at or near an edge load, as in the BEPM, and is sensitive to the degree of viscous coupling at the free edge. Since subducting lithosphere is continuous and generally mechanically coupled to a sinking slab, the BEPM may falsely introduce a weakness and hence overestimateTeat a trench because of trade-off. This could explain the results of recent modelling studies that suggest the rheology of subducting oceanic plate is stronger than that of its interior. However, further studies using more advanced thermal and mechanical models will be required in the future in order to quantify this.