Melting of subducted mélange can potentially transport mass from the slab-mantle interface to the mantle wedge in subduction zones. The mélange diapir model was primarily proposed from the results of laboratory experiments and thermodynamic modeling. However, the melting mechanisms of mélange diapirs in subduction zones remain unclear. To further constrain the mantle dynamics of a mélange diapir, we studied Oligocene alkaline intermediate rocks on the northeast Asian continental margin. We report whole-rock geochemical and Sr-Nd-Pb-Mg-Zn isotope data and show that these rocks formed by partial melting of mélange. We conclude that a diapir was the mechanism for Oligocene melting of the mélange. We also identified younger rocks formed by melting of mélange in the eastern part of northeast Asia, implying an eastward shift in such magmatism since the Oligocene. Our results and the tectonic setting indicate that melting of mélange diapirs occurred preferentially during tectonic transitions, such as the formation of a back-arc basin triggered by trench-perpendicular mantle flow. The low-viscosity mantle with an incompressible stress field triggered melting of the mélange diapirs. Interactions occurred between the mélange diapirs and carbonated peridotites, constraining the depth of mélange-mantle interactions to the asthenosphere, which is deeper than the depth inferred in previous studies.

中文翻译：

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东北亚渐新世俯冲混杂岩熔融及其地幔动力学


俯冲混杂岩的熔化可能会将质量从板片-地幔界面转移到俯冲带中的地幔楔。混杂底辟模型主要是根据实验室实验和热力学建模的结果提出的。然而，俯冲带混杂底辟的熔融机制仍不清楚。为了进一步限制混杂底辟的地幔动力学，我们研究了东北亚大陆边缘的渐新世碱性中间岩。我们报告了全岩地球化学和 Sr-Nd-Pb-Mg-Zn 同位素数据，并表明这些岩石是由混杂岩部分熔融形成的。我们得出的结论是，底辟是渐新世混杂岩熔化的机制。我们还在东北亚东部发现了由混杂岩融化形成的较年轻的岩石，这意味着自渐新世以来此类岩浆活动向东转移。我们的结果和构造环境表明，混杂底辟的熔融优先发生在构造转变期间，例如由海沟垂直地幔流触发的弧后盆地的形成。具有不可压缩应力场的低粘度地幔引发了混杂底辟的熔化。混杂岩底辟和碳化橄榄岩之间发生相互作用，限制了混杂岩-地幔相互作用到软流圈的深度，该深度比先前研究推断的深度要深。