Collaborative Research: Investigating the Role of Mantle Metasomatism and Melt-Rock Interaction During Evolution of Continental Lithosphere Mantle

地球上构造板块最古老的部分位于大陆内部，通常远离板块边界。大陆板块的这些所谓的“克拉通”部分比平均厚度更厚，并在数十亿年内保持稳定，抵抗内部变形。克拉通通常被较年轻的构造板块物质包围，这些板块物质通过吸积和碰撞过程而增加。然而，有地质证据表明，在某些地方，大陆板块厚厚的克拉通内部已经不稳定并被移走(例如，北中国克拉通和美国西南部)。一个根本的问题是：为什么一些克拉通地区能够变形/移除，而另一些地区却稳定了数十亿年？更具体地说，需要什么条件来削弱大陆构造板块内部的不稳定并为其做好准备？为了研究这个问题，这个项目将把北美西南部作为一个天然的实验室，探索岩浆渗入大陆板块可能在破坏克拉通稳定中所起的作用。该研究区具有广泛的新生代火山史，这表明，在北美西南部发生剧烈不稳定之前，经历了一段大规模的岩浆渗入时期(由法拉隆板块俯冲洋壳从北美大陆底部移走引发)，导致板块减薄和现今盆地和山脉省的变形特征。这项研究的一个主要特点是将有关火山岩化学的信息与岩浆在岩石样品中流动的实验室实验和岩浆在多孔材料中流动的数值模型相结合。为了对岩浆如何(A)在大陆构造板块中移动和(B)在板块移动时改造板块，达成面向过程的理解，所有这些方法都是必要的。我们的目标是检验这一假设，即岩浆渗透可能在大陆板块克拉通内部的削弱和不稳定中发挥重要作用。该团队(两名女性和一名男性)代表了处于不同职业阶段的科学家，并在美国西南部两个重要的少数族裔服务机构之间建立了联系。在板块构造理论中，大陆岩石圈地幔弱化和迁移的动力学过程的时间尺度普遍缺乏约束。通过重新评估年龄与地球化学数据之间的关系，特别是同位素和微量元素丰度，我们提出了北美西南部火山作用与构造作用之间的关系的重新解释。这里的工作将检验这一假说，即使北美西南部岩石圈失稳的关键过程发生在与弧有关的岩浆作用之后，以及在褐沸石爆发之前和期间：即与西南法拉隆板块平角/浅角俯冲的岩浆时期有关的区域规模的水化和交代作用。在这个项目中，我们通过详细的火山岩地球化学数据的时空成分分析和两套高压多锤岩石学实验来验证这一假说。这两项工作将为旨在研究CLM/熔体相互作用和/或原位熔融对CLM上升熔体组成和流变学的影响的数值实验提供信息。地球化学分析将包括NAVDAT数据库的数据挖掘以及新的样本收集，特别重要的是，现有数据集的一个关键缺口是大陆内陆，特别是新墨西哥州南部的拉莱姆火山岩。两套多锤实验将研究(1)微量元素在熔体-岩石界面上的扩散，并确定相关的扩散常数；(2)交代的CLM在熔体-岩石界面产生原位熔融中的作用。数值实验将使用来自地球化学和多砧板数据集的数据来构建熔体-岩石相互作用的流态化模型，该模型解决了从一维到三维多孔流模型中的热和化学不平衡条件。该奖项反映了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 oldest parts of tectonic plates on Earth are found in the interiors of continents, usually far from plate boundaries. These so-called “cratonic” portions of continental plates are thicker than average and remain stable for billions of years, resisting internal deformation. Cratons are usually surrounded by younger tectonic plate material, added on through the processes of accretion and collision. However, there is geologic evidence that in some locations the thick cratonic interior portion of continental plates has been destabilized and removed (e.g., the North China Craton and the southwest U.S.). A fundamental question is: why are some cratonic regions able to be deformed/removed while others are stable for billions of years? More specifically, what conditions are needed to weaken and prime the interior of a continental tectonic plate for destabilization? To investigate this question, this project will use southwest North America as a natural laboratory to explore the role that magmas infiltrating through continental plates may play in destabilizing cratons. The study area has an extensive Cenozoic volcanic history that shows that a period of voluminous magma-infiltration (triggered by the removal of subducting oceanic crust of the Farallon plate from the base of the North American continent) preceded a dramatic destabilization of the interior part of southwest North America, leading to thinning of the plate and deformation characteristic of the present-day Basin and Range Province. A key feature of this study is to combine information on the chemistry of the volcanic rocks with laboratory experiments on magma moving through rock samples and numerical models of the flow of magma inside a porous material. All of these approaches are necessary to arrive at a process-oriented understanding of how magma might (a) move through continental tectonic plates and (b) modify the plate as it moves. Our goal is to test the hypothesis that magma-infiltration may play an important role in the weakening and destabilization of the cratonic interiors of continental plates. The team (two female and one male) represents scientists at various career stages and forges a connection between two important minority-serving institutions within the southwestern US. Within the theory of plate tectonics, constraints for the timescales of the dynamic process of continental lithospheric mantle weakening and removal are generally lacking. By reassessing the relationship between age and geochemical data, in particular isotopic and trace element abundances, we propose a reinterpretation for the relationship between volcanism and tectonism in southwest North America. The work here will test the hypothesis that the key processes that preconditioned the southwest North America lithosphere for destabilization took place after arc-related magmatism, and before and during the ignimbrite flare-up: namely, regional-scale hydration and metasomatism associated with the amagmatic period of flat/shallow angle subduction of the Farallon plate beneath SWNA. In this project, we test this hypothesis through detailed space-time-composition analyses of volcanic rock geochemical data and through two suites of high-pressure multianvil petrologic experiments. Both efforts will inform numerical experiments designed to investigate the effects of CLM/melt interaction and/or in situ melting on ascending melt compositions and rheology of the CLM. Geochemical analysis will consist of data mining of the NAVDAT database as well as new sample collection, of particular importance is a critical gap in the available data set is represented by Laramide volcanic rocks in the continental interior, specifically in southern New Mexico. The two suites of multianvil experiments will investigate (1) the diffusion of trace elements across the melt-rock interface and determine the relevant diffusion constants; and (2) the role of metasomatized CLM in generating in situ melting at the melt-rock interface. Numerical experiments will use the data combined from the geochemical and multianvil datasets to build fluidized flow models for melt-rock interactions that address both thermal and chemical disequilibrium conditions building from 1D to 3D porous flow models.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.