At the subduction zone interface, a combination of mechanical deformation and (fluid-mediated) chemical mixing of oceanic crust, sediment and mantle lithologies yields heterogeneous mélange lithologies. These mélanges have compositions and metamorphic mineral assemblages dissimilar to their endmember source lithologies, resulting in a subduction zone interface with physical properties (e.g., H₂O capacity, density, and viscosity) that are distinct from both the source lithologies and simple mechanical mixtures of these lithologies. Using phase equilibria modeling, we find that a large range of mélange compositions carry more H₂O to sub-arc depths and are less dense compared to equivalent mechanical mixtures. We further show that mélange is much weaker than the overlying mantle but remains stronger than quartzite deforming by dislocation creep. Lastly, we synthesize these results and find that at all subduction zones, a range of mélange compositions are likely to form diapirs at sub-arc depths and sub-solidus temperatures.

中文翻译：

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混合体形成对俯冲带界面流变学和 H2O 预算的影响，以及对底辟成核的影响


在俯冲带界面处，机械变形和海洋地壳、沉积物和地幔岩性（流体介导的）化学混合相结合，产生了非均质的混合岩性。这些混合岩的成分和变质矿物组合与其端元源岩性不同，导致俯冲带界面的物理特性（例如，H ₂ O 容量、密度和粘度）与源岩性和这些岩性的简单机械混合物不同。使用相平衡建模，我们发现与等效的机械混合物相比，大范围的混色成分在亚弧深度携带更多的 H ₂ O，并且密度较低。我们进一步表明，mélange 比上覆的地幔弱得多，但仍然比由位错蠕变变形的石英岩更强。最后，我们综合了这些结果，发现在所有俯冲带中，一系列混合成分可能在亚弧深度和亚固相线温度下形成底辟。