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。俯冲带是海洋板块下沉到地球深部的构造边界。这一过程引发了地球深处的融化，形成了火山岛弧，并随着时间的推移形成了大陆地壳。弧形火山由于暴露在地球表面而得到了广泛的研究。然而，岛弧的根部很难接触到，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方面起着至关重要的作用。由于其高密度，弧根被假设为定期从弧的浅层和密度较低的部分分离(剥离)，并沉入地球，随着时间的推移改变块状大陆地壳的组成。重要的是，深弧根的粘性，以及它们被分离的可能性，取决于它们的组成，特别是水。这项研究将为材料如何从火山弧根中剥离或移除提供新的限制。该团队将把最先进的挥发性分析与天然样品的流变学测量结合起来，并将其整合到数值模型中。大陆的形成和演化是一个广泛的科学界感兴趣的活跃话题，如果没有大陆，陆地上就不可能有生命。自从观察到大部分大陆地壳的成分是安山岩，但来自地幔的母质熔体大多是玄武岩以来，人们一直在争论地壳，特别是大陆壳的形成过程。许多研究表明，剥离作用--弧底致密的镁铁质岩石经常沉入地幔的过程--可能解释了大陆地壳和地幔熔体之间的化学差距。其他研究提出，仅有分层不足以解释这种差异。目前，对这一过程的数值模拟有两个主要限制：(1)当前模型中使用的粘度与自然弧形堆积体上的水分测量没有联系，因为这些现场分析从未进行过；(2)假设分离的材料最初是各向同性的，尽管自然堆积体样本显示出广泛的纹理和内部变形。这是一个新的跨学科项目，侧重于水在来自四个弧形背景的下地壳堆积物中的化学和流变学作用。其目标是利用独特的地球化学、流变学和数值方法的组合，研究水、变形和俯冲带中较低的地壳稳定性之间的相互作用。这个合作项目将支持两名博士生和一名博士后研究员的培训。此外，PI将为帕金斯盲人学校(MA)的K-12学生量身定做一门构造学课程。他们还将提供本科生实习机会，并积极努力招收有前途的少数族裔学生。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.