Besides standard thermo-mechanical conservation laws, a general description of mantle magmatism requires the simultaneous consideration of phase changes (e.g. from solid to liquid), chemical reactions (i.e. exchange of chemical components) and multiple dynamic phases (e.g. liquid percolating through a deforming matrix). Typically, these processes evolve at different rates, over multiple spatial scales and exhibit complex feedback loops and disequilibrium features. Partially as a result of these complexities, integrated descriptions of the thermal, mechanical and chemical evolution of mantle magmatism have been challenging for numerical models. Here we present a conceptual and numerical model that provides a versatile platform to study the dynamics and nonlinear feedbacks inherent in mantle magmatism and to make quantitative comparisons between petrological and geochemical datasets. Our model is based on the combination of three main modules: (1) a Two-Phase, Multi-Component, Reactive Transport module that describes how liquids and solids evolve in space and time; (2) a melting formalism, called Dynamic Disequilibirum Melting, based on thermodynamic grounds and capable of describing the chemical exchange of major elements between phases in disequilibrium; (3) a grain-scale model for diffusion-controlled trace-element mass transfer. We illustrate some of the benefits of the model by analyzing both major and trace elements during mantle magmatism in a mid-ocean ridge-like context. We systematically explore the effects of mantle potential temperature, upwelling velocity, degree of equilibrium and hetererogeneous sources on the compositional variability of melts and residual peridotites. Our model not only reproduces the main thermo-chemical features of decompression melting but also predicts counter-intuitive differentiation trends as a consequence of phase changes and transport occurring in disequilibrium. These include a negative correlation between Na₂O and FeO in melts generated at the same T_p and the continued increase of the melt’s CaO/Al₂O₃ after Cpx exhaustion. Our model results also emphasize the role of disequilibrium arising from diffusion for the interpretation of trace-element signatures. The latter is shown to be able to reconcile the major- and trace-element compositions of abyssal peridotites with field evidence indicating extensive reaction between peridotites and melts. The combination of chemical disequilibrium of major elements and sluggish diffusion of trace elements may also result in weakened middle rare earth to heavy rare earth depletion comparable with the effect of residual garnet in mid-ocean ridge basalt, despite its absence in the modelled melts source. We also find that the crystallization of basalts ascending in disequilibrium through the asthenospheric mantle could be responsible for the formation of olivine gabbros and wehrlites that are observed in the deep sections of ophiolites. The presented framework is general and readily extendable to accommodate additional processes of geological relevance (e.g. melting in the presence of volatiles and/or of complex heterogeneous sources, refertilization of the lithospheric mantle, magma channelization and shallow processes) and the implementation of other geochemical and isotopic proxies. Here we illustrate the effect of heterogeneous sources on the thermo-mechanical-chemical evolution of melts and residues using a mixed peridotite–pyroxenite source.

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地幔岩浆作用的非平衡反应输运模型

除了标准的热机械守恒定律外，对地幔岩浆作用的一般描述还需要同时考虑相变（例如，从固体到液体），化学反应（即，化学成分的交换）和多个动态相（例如，液体通过变形矩阵渗滤） ）。通常，这些过程在多个空间尺度上以不同的速率演化，并表现出复杂的反馈回路和不平衡特征。这些复杂性的部分结果是，对于地幔岩浆作用的热，机械和化学演化的综合描述对于数值模型来说是具有挑战性的。在这里，我们提供了一个概念模型和数值模型，为研究地幔岩浆作用固有的动力学和非线性反馈以及岩石学和地球化学数据集之间的定量比较提供了一个通用平台。我们的模型基于三个主要模块的组合：（1）两相，多组分，反应性运输模块，描述了液体和固体在空间和时间上的演化方式；（2）一种基于热力学基础的熔融形式主义，称为动态不平衡熔化，能够描述不平衡相之间主要元素的化学交换；（3）扩散控制的痕量元素传质的晶粒度模型。我们通过分析洋中脊状背景下的地幔岩浆作用期间的主要和微量元素，说明了该模型的某些优点。我们系统地研究了地幔潜在温度，上升流速度，平衡度和非均质源对熔体和残余橄榄岩组成变异的影响。我们的模型不仅再现了减压融化的主要热化学特征，而且还预测了由于相变和不平衡中发生的输运而产生的反直觉的分化趋势。这些包括Na之间的负相关 我们的模型不仅再现了减压融化的主要热化学特征，而且还预测了由于相变和不平衡中发生的输运而产生的反直觉的分化趋势。这些包括Na之间的负相关 我们的模型不仅再现了减压融化的主要热化学特征，而且还预测了由于相变和不平衡中发生的输运而产生的反直觉的分化趋势。这些包括Na之间的负相关在相同的T _p下生成的熔体中的₂ O和FeO以及熔体的CaO / Al ₂ O ₃的持续增加在Cpx耗尽后。我们的模型结果还强调了扩散引起的不平衡在微量元素签名解释中的作用。后者被证明能够调和深海橄榄岩的主要和微量元素组成，并有现场证据表明橄榄岩和熔体之间发生了广泛的反应。主要元素的化学不平衡和微量元素的缓慢扩散的结合也可能导致中稀土到重稀土的消耗减弱，这与洋中脊玄武岩中残留石榴石的作用相当，尽管在模拟熔体源中没有残留石榴石。我们还发现玄武岩通过软流圈地幔不平衡上升的结晶可能是在蛇绿岩深部观察到的橄榄石辉长岩和辉绿岩的形成。所提出的框架是一般性的，并且易于扩展，以适应其他与地质相关的过程（例如，在挥发物和/或复杂的非均质源存在下的融化，岩石圈地幔的转导，岩浆通道化和浅层过程）以及其他地球化学方法的实施。同位素代理。在这里，我们说明了使用橄榄岩-辉石岩混合源对熔体和残留物的热机械化学演化的影响。所提出的框架是一般性的，并且易于扩展，以适应其他与地质相关的过程（例如，在挥发物和/或复杂的非均质源存在下的融化，岩石圈地幔的转导，岩浆通道化和浅层过程）以及其他地球化学方法的实施。同位素代理。在这里，我们说明了使用橄榄岩-辉石岩混合源对熔体和残留物的热机械化学演化的影响。所提出的框架是一般性的，并且易于扩展，以适应其他与地质相关的过程（例如，在挥发物和/或复杂的非均质源存在下的融化，岩石圈地幔的转导，岩浆通道化和浅层过程）以及其他地球化学方法的实施。同位素代理。在这里，我们说明了使用橄榄岩-辉石岩混合源对熔体和残留物的热机械化学演化的影响。