Collaborative Research: Understanding the Origin of the mid-lithospheric discontinuity within a stable continent from a combined geophysics-mineral physics approach

合作研究：通过地球物理学-矿物物理学相结合的方法了解稳定大陆内岩石圈中部不连续性的起源

• 批准号: 1818792
• 负责人: Shun-ichiro Karato
• 金额: $ 43.49万
• 依托单位: Yale 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: 2018-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1818792&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; Origin; mid

In stable continents worldwide, a substantial velocity decrease has been detected at about 100 km depth (varying depending on region) and at an expected temperature of about 1000 degrees C. This decrease in velocity of roughly 3-5% or more, is called the mid-lithosphere discontinuity (MLD). The lithosphere (hard rocks) of a stable continent is expected to be old, and cold, therefore observations of a geological wide-spread discontinuity in seismic velocity internal to the lithosphere is puzzling. This has led to a variety of different, often contradictory, explanatory models for a wavespeed drop within stable lithosphere, e.g., partial melt, anisotropy, sub-solidus rheology transitions, and chemical stratification. This project will evaluate these proposed causative models against new geophysical and geological constraints, using EarthScope data, laboratory experiments and computer modelling. The project will focus on (1) variation in elastic and anelastic properties and electrical conductivity across the MLD, (2) a global presence of the MLD, regardless of geological history, (3) laboratory studies of the influence of water (hydration) on properties of rock that could cause the velocity to increase, and (3) composition and textures of mantle xenoliths, samples of solid mantle rock that hitch a ride with rising magma. This project will engage early career scientists, Ph.D. students, and undergraduate students. The project will also promote EarthScope's education and outreach goals, by presenting the science results and research opportunities at the IRIS minority recruitment speaker series and the Nifty Fifty science lectures to K-12 educators and students.The project will: (1) extend the seismological observations using new receiver-function estimates and Bayesian methodology that can quantify the magnitude of anisotropy and the sharpness of the velocity drop over a more extensive footprint of seismic stations; (2) acquire measurements of surface wave amplitudes and Pg reverberation coda to identify whether there is a peak in attenuation around the MLD depth; and (3) jointly integrate magnetotelluric (MT) conductivity estimates with new mineral-physics and seismological constraints, to identify the presence of melt or hydration across the MLD. The investigators will focus the study on the stable Precambrian North American Craton, which was covered by the second half of the lower-48 deployment of the EarthScope Transportable Array. The project will also involve new lab experiments on how water influences grain-boundary mobility in mantle rocks. An improved understanding of the MLD is crucial for relating EarthScope results to the evolution of continents. The extension of the seismological observation and its integration with MT and mineral physics is a unique approach that will provide new insights into the origin of the MLD. These new strategies for processing seismic data and integrating MT data with seismology and mineral physics will be useful to the general geophysical community. With this interdisciplinary hypothesis-testing approach, the investigators propose to obtain a better understanding of the cause of the MLD that will extend the initial studies of USArray data to the structure and evolution of the North American continent, and by analogy, to other continents.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.

在全球稳定的大陆，在大约100 km的深度（根据区域而变化）和预期温度约为1000度的情况下，检测到大幅度降低的速度。中间层不连续性（MLD）。 稳定大陆的岩石圈（硬岩）预计将是旧的，因此对地震速度内部地震速度的地质广泛不连续性的观察令人困惑。 这导致了各种不同的，通常是矛盾的解释性模型，用于稳定岩石​​圈内的波动下降，例如部分熔体，各向异性，甲状腺果实流变学转变和化学分层。该项目将使用EarthScope数据，实验室实验和计算机建模来评估这些提出的因果关系模型，以针对新的地球物理和地质约束。该项目将重点关注（1）弹性和无弹性特性的变化以及整个MLD的电导率，（2）MLD的全球存在，无论地质历史如何岩石的特性可能导致速度增加，（3）地幔异义石的成分和质地，固体地幔岩石的样品与岩浆上升的骑行。该项目将吸引早期职业科学家博士。学生和本科生。该项目还将通过在IRIS少数民族招聘演讲者系列以及为K-12教育者和学生的Nifty 50科学讲座上介绍科学成果和研究机会，从而促进Earthscope的教育和外展目标。使用新的接收器功能估计值和贝叶斯方法的观察，这些方法可以量化各向异性的大小以及速度的清晰度下降到更广泛的地震站的足迹上； （2）获取表面波幅度和PG混响尾声的测量值，以确定MLD深度周围的衰减峰值； （3）共同将磁电纤维（MT）电导率估计与新的矿物质物质和地震学约束相结合，以确定MLD中熔体或水合的存在。调查人员将将这项研究重点放在稳定的前寒武纪北美克拉顿上，该craton被可运输阵列的下半部分部部部署的下半年所涵盖。该项目还将涉及有关水如何影响地幔岩石晶体边界迁移率的新实验实验。对MLD的改进理解对于将地球景观结果与大陆的演变联系起来至关重要。地震学观察及其与MT和矿物物理学的整合的扩展是一种独特的方法，它将为MLD的起源提供新的见解。 这些新的处理地震数据和将MT数据与地震学和矿物质物理学整合的新策略将对一般地球物理群落有用。通过这种跨学科的假设检验方法，研究人员建议更好地了解MLD的原因，该原因将将USArray数据的初步研究扩展到北美大陆的结构和演变，并以类比为其他大陆。该奖项反映了NSF的法定使命，并通过使用基金会的知识分子和更广泛的影响审查标准进行评估而被认为值得支持。

项目成果

High-resolution mid-mantle imaging with multiple-taper SS -precursor estimates

具有多锥度 SS 前体估计的高分辨率中地幔成像

• DOI: 10.1093/gji/ggac491
• 发表时间: 2022
• 期刊: Geophysical Journal International
• 影响因子: 2.8
• 作者: Frazer, William D.;Park, Jeffrey
• 通讯作者: Park, Jeffrey

A Plan for a Long-Term, Automated, Broadband Seismic Monitoring Network on the Global Seafloor

全球海底长期、自动化、宽带地震监测网络计划

• DOI: 10.1785/0220190123
• 发表时间: 2020
• 期刊: Seismological Research Letters
• 影响因子: 3.3
• 作者: Kohler, Monica D.;Hafner, Katrin;Park, Jeffrey;Irving, Jessica C.;Caplan-Auerbach, Jackie;Collins, John;Berger, Jonathan;Tréhu, Anne M.;Romanowicz, Barbara;Woodward, Robert L.
• 通讯作者: Woodward, Robert L.

Anisotropic Layering and Seismic Body Waves: Deformation Gradients, Initial S-Polarizations, and Converted-Wave Birefringence

• DOI: 10.1007/s00024-021-02755-6
• 发表时间: 2021-05
• 期刊: Pure and Applied Geophysics
• 影响因子: 2
• 作者: Xiaoran Chen;Jeffrey Park;V. Levin

Crustal Anisotropy from the Birefringence of P-to-S Converted Waves: Bias Associated with P-Wave Anisotropy

P-S 转换波双折射的地壳各向异性：与 P 波各向异性相关的偏差

• DOI: 10.4401/ag-8882
• 发表时间: 2023
• 期刊: Annals of Geophysics
• 影响因子: 1
• 作者: Park, Jeffrey;Chen, Xiaoran;Levin, Vadim
• 通讯作者: Levin, Vadim

Effects of pressure on diffusion creep in wet olivine aggregates

• DOI: 10.1016/j.pepi.2022.106840
• 发表时间: 2022-01
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: R. Silber;J. Girard;S. Karato