CSEDI Collaborative Research: C-O-H Volatile Metasomatism in the Cratonic Mantle - Implications for Mid-Lithospheric Discontinuities

CSEDI 合作研究：克拉通地幔中的 C-O-H 挥发性交代作用 - 对中岩石圈间断面的影响

• 批准号: 1763243
• 负责人: Karen Fischer
• 金额: $ 12.76万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-05-01 至 2021-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1763243&HistoricalAwards=false
• 关键词: CSEDI; Collaborative; Research; Volatile; Metasomatism

Earth is the only planet in the Solar System whose surface is divided into oceans and continents. Hence understanding the origin of continents and how portions of them remain stable for billions of years is central to understanding the evolution of the Earth. The old, stable cores of continents (cratons) are underlain by thick layers of mantle (the silicate layer of the Earth that lies below the crust), and these mantle roots are thought to contribute to continental stability. Yet, it remains debated how the continental mantle formed and evolved. In particular, the roles of magma or fluid interaction with the mantle, either during or after the continent formation, are unclear, although widespread layering observed in the cratonic mantle by seismic imaging may have been created by magma and fluid related processes. This research will constrain the formation and evolution of cratons by bracketing scenarios of melt/fluid and mantle reactions that are consistent with geophysical observations at mid-lithospheric depths. The research findings - disseminated through peer-reviewed publications, conference presentations and colloquia, and class room lectures and activities - will impact a wide range of Earth science sub-disciplines including petrology-geochemistry, mineral physics, geodynamics, and seismology. The proposal will support female PhD students in high P-T experimental petrology, mineral physics, and seismology, and support the research activities of several undergraduate students, including students from underrepresented groups. In addition to their own research, all the students will participate in discussions and write research articles together with all 3 PIs, learning how to combine concepts and methods from three different yet related sub-disciplines of solid Earth science. The proposal will thus directly further the educational experience and professional development of several students at various stages of their careers. The proposed research will also support an early career PI in the field of mineral physics and will aid the investigators in engaging K-12 students in science.The stability of the continental interiors for 2-3 billion years is a key feature of the Earth's dynamical and thermal evolution. Understanding the geophysical structure, petrology, and material properties of cratonic mantles and the tectonic history that produced them is therefore one of the grand challenges of Earth science. A curious feature of subcontinental mantles is the presence of distinct reductions in seismic shear velocity at depths of 60-150 km, often called mid-lithospheric discontinuities (MLDs). Given the widespread occurrence of MLDs within cratons, their origins may be linked to craton formation; however, the causal link between MLD and craton formation is yet to be established, and MLD origins remain highly debated. One hypothesis is that MLDs represent zones enriched in CO2-H2O volatiles, which led to stability of hydrous and/or carbonate minerals or partial melts. This project will test this hypothesis by integrating results from experimental petrology, mineral physics, and seismology. Through laboratory experiments, this project will constrain the phase equilibria of cratonic mantle peridotites fluxed by mixed CO2-H2O volatiles at MLD depths, taking into consideration how the agent of volatile introduction may vary with craton formation models. The goal will be to determine the stability of hydrous and carbonate mineral phases over partial melts and obtain the compositions and proportions of mineral phases as a function of depth, temperature, and melt/fluid:peridotite ratio for each of the cases. Guided by the phase equilibria experiments and compiled xenolith data, thermoelastic properties of the appropriate end members and intermediate solid solutions of amphibole and mica will be determined using Resonant Ultrasound Spectroscopy (RUS) and first principles simulation. Using the mineral assemblages from experiments and updated elasticity data from new mineral physics, mantle velocity models will be predicted. These will be compared to mantle models for southern African craton (to be obtained by joint inversion of surface wave, Sp and Ps data) and North America, and used to calculate synthetic Sp and Ps receiver function stacks that will be compared to MLD observations globally. The proposed research will test whether one or several scenarios of fluid/melt infiltration into cratons, if any, satisfy the geophysical and petrologic characters of continental mantles at mid-lithospheric depths. Our research will also lead to specific products such as solidus parameterizations of depleted mantle+CO2+H2O; metasomatized mantle mineral assemblages as a function of P-T, infiltrated fluid/melt composition and fluid/melt:rock ratio; codes for computing seismic velocities for MLD-related assemblages with updated thermoelastic data; and observed mantle discontinuity parameters and mantle velocity 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.

地球是太阳系中唯一将表面分为海洋和大陆的行星。因此，了解大陆的起源及其部分在数十亿年内如何保持稳定对于理解地球的演变至关重要。旧大陆（cratons）的旧岩心在地幔层（地下位于地壳以下的地球的硅酸盐层）的底部，并且这些地幔根被认为有助于大陆稳定性。然而，它仍然在争论大陆地幔如何形成和进化。特别是，在大陆形成期间或之后，岩浆或流体与地幔的相互作用的作用尚不清楚，尽管通过地震成像在克拉托式地幔中观察到的广泛分层可能是由岩浆和相关的流体过程创建的。这项研究将通过融化/流体和地幔反应的括号情景来限制克拉通的形成和演变，这些情景与地球中部深度中的地球物理观测一致。通过同行评审的出版物，会议演讲和座谈会以及教室的讲座和活动传播的研究结果将影响广泛的地球科学子学科，包括岩石学 - 地球化学，矿物质物理学，地球动力学和地震学。该提案将为高P-T实验性质学，矿物质物理学和地震学的女性博士学位学生提供支持，并支持几位本科生的研究活动，包括来自代表性不足的群体的学生。除了自己的研究外，所有学生还将参与讨论并撰写研究文章以及所有3个PI，学习如何结合三个固体地球科学的三个不同但相关但相关的子学科的概念和方法。因此，该提案将直接进一步促进几名学生职业生涯的多个学生的教育经验和专业发展。拟议的研究还将支持矿物质物理领域的早期职业生涯，并将帮助研究人员参与K-12学生参与科学。大陆室内设计的稳定性已有2 - 3亿年是地球动力和热进化的关键特征。因此，了解克拉通披风的地球物理结构，岩石学和物质特性以及产生它们的构造历史是地球科学的巨大挑战之一。次大披风的一个奇怪特征是在60-150 km的深度下，地震剪切速度的显着降低，通常称为中间层中部不连续性（MLDS）。鉴于Craton中MLD的广泛发生，它们的起源可能与Craton的形成有关。但是，MLD与Craton形成之间的因果关系尚未建立，MLD的起源仍然高度争议。一种假设是，MLDS代表富含CO2-H2O挥发物的区域，从而导致含水和/或碳酸盐矿物质或部分熔体的稳定性。该项目将通过整合实验性岩石学，矿物质物理学和地震学的结果来检验这一假设。通过实验室实验，该项目将限制由MLD深度的混合CO2-H2O挥发物在MLD深度上通过混合的co2-H2O挥发物的相位平衡，考虑到挥发性引入的推动者可能如何随craton形成模型而变化。目的是确定含水和碳酸盐矿物相在部分熔体上的稳定性，并获得矿物相的组成和比例，这是每种情况的深度，温度和熔体/流体的函数：植酸岩的组成和植物含量。在相位平衡实验和编译异种石数据的指导下，将使用谐振超声光谱（RUS）和第一原理模拟确定适当最终构件的热弹性和闪比尔和云母的中间固体溶液。使用来自实验的矿物组合和新矿物物理学的更新弹性数据，将预测地幔速度模型。这些将与南部非洲克拉通的地幔模型进行比较（通过表面波，SP和PS数据的联合反转获得）和北美，并用于计算合成的SP和PS接收器功能堆栈，这些堆栈将与全球MLD观测值进行比较。拟议的研究将测试一种或几种液体/熔体浸润是否会渗入cratons（如果有的话），以满足大陆地幔的地球物理和岩石学特征。我们的研究还将导致特定产品，例如耗尽的地幔+CO2+H2O的固体参数化；交代的地幔矿物组合与P-T的关系，浸润的流体/熔体组成和液体/熔体：岩石比；计算与MLD相关组合的地震速度的代码，并具有更新的热弹性数据；并观察到的地幔不连续参数和地幔速度模型。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响标准，被认为值得通过评估来获得支持。

项目成果

Global Patterns in Cratonic Mid‐Lithospheric Discontinuities From Sp Receiver Functions

• DOI: 10.1029/2021gc009819
• 发表时间: 2021-06
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: H. E. Krueger;I. Gama;K. Fischer