Collaborative Research: Melange-peridotite Interactions In The Source of Arc Magmas

俯冲带是富含水的海洋板块沉入地球深处的构造边界。这一过程与一系列地质灾害有关，如9级特大逆冲地震和爆炸性弧火山活动。今天，数百万人生活在可能暴露于俯冲带危险的地区，包括卡斯卡迪亚和阿拉斯加的大片地区。然而，富含水的岩石从下行板块转移到地球内部的机制，以及这种转移过程对地质灾害的影响，在很大程度上仍然未知。研究俯冲带中物质转移的最佳岩石样本是来自板块顶部的称为混杂岩（“混合”岩）的独特岩石。尽管这些岩石在大多数俯冲带模型中被忽视，但它们可能在弧熔岩的形成中发挥重要作用，并对俯冲带的地球动力学产生强烈影响。这个项目将结合高压、高温混合材料的实验室实验和数值模拟来量化地球内部的这种转移过程。这种变革性和跨学科的方法将为melange在俯冲带危险发展中的作用提供新的约束，并为研究生、本科生和K-12学生提供培训机会。俯冲带的常规模型预测，在弧岩浆中观察到的微量元素分馏发生在两个不同的事件中：(a)变质海洋地壳的脱水和流体释放，以及(b)板块-地幔界面沉积物的部分熔融。然而，以前没有实验研究通过模拟这种传统模型来重现弧岩浆的化学性质。相比之下，其他研究认为流体、沉积物和蛇纹石化的楔块在板幔界面混合形成混杂岩，混合岩由蚀变的海洋地壳和沉积物块体组成，与蛇纹石化的橄榄岩混合。随着板块的下降，板块顶部形成的混杂岩可能部分熔化，并直接在板块-地幔界面产生典型的弧岩浆微量元素分馏。或者，混杂岩可能以固体底辟的形式从板幔界面上升，在上升过程中部分熔融，延迟了微量元素分馏作用的发生。在这两种情况下，混合岩熔体在到达地表的过程中都会与橄榄岩地幔楔发生反应，将它们的化学特征与地幔的化学特征结合起来。该项目将结合一系列高压、高温实验和数值模拟来研究俯冲带天然混杂岩的化学和物理行为。实验和模拟相结合的结果将为评估混杂岩在俯冲带岩浆活动中的作用提供一种变革性的方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones are tectonic boundaries where water-rich oceanic plates sink back into the Earth's deep interior. This process is associated with a large array of geological hazards such as magnitude 9 megathrust earthquakes and explosive arc volcanism. Today, millions of people live in areas that are potentially exposed to subduction zone hazards, including large regions of Cascadia and Alaska. However, the mechanisms by which water-rich rocks are transferred from the down-going plate (slab) into the Earth's interior, and the consequences of this transfer process on geological hazards, remain largely unknown. The best rock samples to study material transfer in subduction zones are unique rocks called melanges ('mixed' rocks) that come from the top of the slab. Although largely overlooked in most subduction zone models, these rocks may play a significant role in the generation of arc lavas, and strongly influence the geodynamics of subduction zones. This project will combine high-pressure, high-temperature laboratory experiments on melange materials with numerical modeling to quantify this transfer process in the Earth's interior. This transformative and interdisciplinary approach will provide novel constraints on the role of melanges in the development of subduction zone hazards, as well as training opportunities for graduate, undergraduate, and K-12 students.Conventional models of subduction zones predict that trace element fractionations observed in arc magmas occur during two distinct events: (a) dehydration and release of fluids from altered oceanic crust, and (b) partial melting of sediments at the slab-mantle interface. However, no previous experimental studies have reproduced the chemistry of arc magmas by simulating this conventional model. By contrast, other studies argue that fluids, sediments, and serpentinized wedge mix together at the slab-mantle interface to form melanges, which are hybrid rocks composed of blocks of altered oceanic crust and sediments, mixed with serpentinized peridotite. As the slab descends, melanges formed at the top of the slab may partially melt and produce trace element fractionation typical of arc magmas directly at the slab-mantle interface. Alternatively, melanges may rise from the slab-mantle interface as solid diapirs and partially melt during their ascent, delaying the onset of trace element fractionation. In both scenarios, melange melts would react with the peridotite mantle wedge on their way to the surface, combining their chemical characteristics with that of the mantle. This project will combine a series of high-pressure, high-temperature experiments with numerical modeling to investigate the chemical and physical behavior of natural melange rocks in subduction zones. The combined experimental and modeling results will provide a transformative approach to assess the role of melanges in subduction zone magmatism.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.