Collaborative Research: Voyage to the bottom of Arcs: interplay between water, deformation, and lower crustal stability

大陆的形成与地球上的板块构造密切相关。俯冲带是大洋板块沉入地球内部深处的构造边界。随着时间的推移，这一过程引发了地球深处的融化、火山岛弧的形成以及大陆地壳的形成。由于弧火山暴露在地球表面，人们对它们进行了很好的研究。然而，岛弧的根源很难接近，因此，研究仍然很少。深弧根在控制大陆地壳和整个地球系统的演化中起着至关重要的作用。由于它们的高密度，弧根被假设有规律地从弧的浅层和密度较低的部分分离（分层），并沉回地球，随着时间的推移改变了大块大陆地壳的组成。重要的是，深弧根的粘性特性，以及它们被分离的可能性，取决于它们的成分，尤其是水。这项研究将为如何从火山弧根部剥离或移除物质提供新的限制。该团队将把最先进的挥发性分析与自然样品的流变测量相结合，并将其整合到数值模型中。大陆的形成和演化是广泛科学界感兴趣的一个活跃话题，没有大陆就没有陆地上的生命。地壳，特别是大陆地壳的形成过程一直以来都是有争议的，因为人们观察到大陆地壳的主要成分是安山岩，而地幔衍生的母熔融体主要是玄武岩。许多研究表明，分层作用，即弧形底部的致密基性岩石定期沉入地幔的过程，可以解释大块大陆地壳和地幔融化之间的化学间隙。其他研究提出，单凭分层并不足以解释这种差异。目前，这一过程的数值模拟有两个主要的局限性：(1)目前模型中使用的粘度与天然弧形堆积的水测量无关，因为这些原位分析从未进行过；(2)假定分离的材料最初是各向同性的，尽管自然堆积样品具有广泛的纹理和内部变形。这是一个新颖的跨学科项目，重点研究了水在四个弧背景下的下地壳堆积中的化学和流变作用。目的是利用地球化学、流变学和数值方法的独特组合，研究俯冲带中水、变形和下地壳稳定性之间的相互作用。该合作项目将支持2名博士生和1名博士后的培养。此外，pi将为帕金斯盲人学校（MA）的K-12学生量身定制构造课程。他们还将提供本科生实习机会，并积极招收有前途的少数民族学生。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。

The formation of continents is intimately linked to plate tectonics on Earth. Subduction zones are tectonic boundaries where oceanic plates sink back into the Earth's deep interior. This process triggers melting in the deep Earth, the formation of volcanic island arcs, and the building of continental crust over time. Arc volcanos are well-studied due to their exposure at the Earth's surface. However, the roots of island arcs are difficult to access and therefore, remain poorly studied. Deep arc roots play a critical role in controlling the evolution of continental crust and the Earth system as a whole. Due to their high density, arc roots are hypothesized to regularly detach (delaminate) from the shallow and less dense parts of the arc, and sink back into the Earth, modifying the composition of the bulk continental crust over time. Importantly, the viscous nature of deep arc roots, and hence their likelihood of being detached, depends on their composition, particularly water. This study will provide new constraints on how material is delaminated, or removed, from volcanic arc roots. The team will combine state-of-the-art volatile analyses with rheological measurements on natural samples, which will be integrated into numerical models. The formation and evolution of continents, without which no life on land could have developed, is an active topic of interest for the broad scientific community.The processes by which the Earth's crust, and in particular the continental crust, has been constructed over time have been debated since the observation that bulk continental crust is andesitic in composition, but mantle-derived parental melts are mostly basaltic. A number of studies have suggested that delamination, a process by which dense mafic rocks at the base of arcs regularly sink back into the mantle, could account for the chemical gap between bulk continental crust and mantle melts. Other studies have proposed that delamination alone is not sufficient to explain the discrepancy. Currently, numerical simulations of this process have two major limitations: (1) viscosities used in current models are not linked to water measurements on natural arc cumulates because these in-situ analyses have never been performed; and (2) it is assumed that the material that detaches is initially isotropic although natural cumulate samples show a wide range of textures and internal deformation. This is a novel interdisciplinary project that is focused on the chemical and rheological role of water in lower crustal cumulates from four arc settings. The goal is to examine the interplay between water, deformation, and lower crustal stability in subduction zones, using a unique combination of geochemical, rheological, and numerical approaches. This collaborative project will support two Ph.D. students and the training of a postdoctoral investigator. In addition, the PIs will design a tectonics class tailored for K-12 students at the Perkins School for the Blind (MA). They will also offer undergraduate internship opportunities and make an active effort to recruit promising minority students.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.