Collaborative Research: Melange-peridotite Interactions in the Source of Arc Magmas

合作研究：弧岩浆源头中的混杂岩-橄榄岩相互作用

• 批准号: 1852610
• 负责人: Veronique Le Roux
• 金额: $ 42.08万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1852610&HistoricalAwards=false
• 关键词: Collaborative; Research; Melange; peridotite; Interactions

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.

俯冲带是富含水的海洋板块下沉到地球内部深处的构造边界。这一过程与一系列地质灾害有关，如9级大规模地震和爆发性弧火山活动。今天，数百万人生活在可能遭受俯冲带危害的地区，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（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后果，在很大程度上仍然是未知的。研究俯冲带物质转移的最佳岩石样本是来自板块顶部的独特岩石，称为混杂岩（“混合”岩石）。虽然在大多数俯冲带模型中被忽视，但这些岩石可能在弧熔岩的生成中起着重要作用，并强烈影响俯冲带的地球动力学。该项目将把对混杂岩材料进行的联合收割机高压、高温实验室实验与数字建模相结合，以量化地球内部的这种转移过程。这种变革性的跨学科方法将为混杂岩在俯冲带灾害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。俯冲带的传统模型预测，在两个不同的事件期间，在弧岩浆中观察到的微量元素分馏发生：（a）蚀变洋壳的脱水和流体释放;（B）板幔界面沉积物的部分熔融。然而，没有以前的实验研究再现了电弧岩浆的化学模拟这种传统的模型。相比之下，其他研究认为，流体，沉积物和蛇纹化楔在板幔界面混合在一起形成混杂岩，这是由蚀变洋壳和沉积物块组成的混合岩石，混合着蛇纹化橄榄岩。当板块下降时，在板块顶部形成的混杂岩可能部分熔融，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，混杂岩可能上升从板幔界面固体底辟和部分熔融在其上升，延迟微量元素分馏的开始。在这两种情况下，混杂岩熔体将与橄榄岩地幔楔反应的方式到表面，结合自己的化学特性与地幔。本计画将联合收割机结合一系列高压高温实验与数值模拟，探讨俯冲带天然混杂岩的化学与物理行为。结合实验和模拟结果将提供一种变革性的方法来评估混杂岩在俯冲带岩浆活动中的作用。该奖项反映了NSF的法定使命，并被认为值得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来支持。