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

地球上最古老的构造板块位于大陆内部，通常远离板块边界。这些所谓的大陆板块的“板块”部分比平均厚度要厚，并保持稳定数十亿年，抵抗内部变形。 这些板块通常被较年轻的构造板块物质所包围，这些物质是通过吸积和碰撞过程而增加的。然而，有地质证据表明，在某些地方，大陆板块的厚的南极洲内部部分已经不稳定和移动（例如，中国北方和美国西南部）。一个基本的问题是：为什么一些电子区域能够变形/移除，而另一些则稳定数十亿年？ 更具体地说，需要什么样的条件才能削弱大陆构造板块的内部并使其产生不稳定？ 为了研究这个问题，该项目将把北美西南部作为一个天然实验室，探索岩浆渗透大陆板块可能在破坏地壳稳定方面发挥的作用。该研究区有着广泛的新生代火山历史，表明在北美西南部的内部发生剧烈的不稳定之前，有一段时间大量的岩浆渗透（由法拉隆板块的俯冲洋壳从北美大陆的底部移出而引发），导致板块变薄，变形成为当今盆岭省的特征。这项研究的一个主要特点是将火山岩化学成分的联合收割机信息与岩浆在岩石样品中移动的实验室实验和多孔材料中岩浆流动的数值模型相结合。所有这些方法都是必要的，以达到一个面向过程的理解岩浆可能（a）通过大陆构造板块移动和（B）修改板块移动。 我们的目标是测试的假设，岩浆渗透可能发挥了重要作用，在大陆板块的地壳内部的削弱和不稳定。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民族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去除动力学过程的时间尺度一般缺乏约束。通过重新评估年龄和地球化学数据之间的关系，特别是同位素和微量元素丰度，我们提出了一个重新解释北美西南部的火山活动和构造活动之间的关系。在这里的工作将测试的假设，预处理北美西南岩石圈不稳定的关键过程发生在弧相关的岩浆活动后，之前和期间的熔结凝灰岩耀斑：即，区域规模的水化和交代与岩浆期的平面/浅角俯冲的Farallon板块下SWNA。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组成分析，并通过两套高压多砧岩石学实验来验证这一假设。 这两方面的努力将通知数值实验，旨在调查CLM/熔体相互作用和/或原位熔融上升的熔体组合物和流变学的CLM的影响。 地球化学分析将包括NAVDAT数据库的数据挖掘以及新样本的收集，特别重要的是，可用数据集的一个关键空白是大陆内部的Laramide火山岩，特别是在新墨西哥州南部。这两套多砧实验将研究（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;以及（2）交代CLM在熔体-岩石界面产生原位熔融中的作用。数值实验将使用地球化学和多砧数据集的数据相结合，建立熔体-岩石相互作用的流化流模型，解决热和化学不平衡条件，建立从一维到三维的多孔流模型。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.