CSEDI: Compositional heterogeneity and seismic anisotropy near the 410 km discontinuity

CSEDI：410公里间断面附近的成分异质性和地震各向异性

• 批准号: 1664471
• 负责人: Jin Zhang
• 金额: $ 36.99万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1664471&HistoricalAwards=false
• 关键词: CSEDI; Compositional; heterogeneity; seismic; anisotropy

The mantle is the largest compositional layer within Earth and it is continually mixed by thermal convection associated with the movement, creation, and destruction of tectonic plates. It is clear from volcanic rocks that this mixing has not resulted in a homogeneous mantle composition, however, there are few observational constraints that allow mapping of the compositional variations within Earth's mantle. This project seeks to measure the range of compositional variations in the mantle and map their spatial distribution across the globe. The focus will be variations in the fraction of the mineral olivine because it is the most abundant mantle mineral and variations in its local abundance change the properties of a seismically reflective boundary at about 400 km depth. The interface represents a change in the crystal structure of olivine, which transforms to wadsleyite as pressure and temperature increase with depth. Laboratory mineral physics experiments to determine the seismic properties of olivine and wadsleyite will be combined with analyses of seismic data from dense regional arrays to infer compositional variations. In addition to estimating the fraction of olivine, the project will also estimate the abundance of hydrogen defects in olivine, which represent a potential geochemical reservoir of water in the deep Earth. The combined studies will provide novel insights into global mantle mixing and spatial variations in the ability of the mantle to generate volcanic activity. Grant funding will primarily be used to support research training and education of student scientists using modern mineral physics and seismic methods.This project will take advantage of the petrological simplicity of the 410 km discontinuity, which is the boundary between the upper mantle and the transition zone, to investigate spatial variations in the bulk and volatile composition of the mantle. The olivine-wadsleyite transition is the only phase transition that can cause the globally observed 410. Wadsleyite has about five times greater water storage capacity than olivine and the existence of structural water can profoundly affect sound velocities of minerals. Therefore the magnitude of the 410 provides a good estimation of the olivine content and water concentration near 410 km depth in the Earth's interior. High olivine content in the source rock results in less capability of producing magma, thus olivine content is a good indicator of mantle petrology. In addition, olivine is also strongly anisotropic relative to wadsleyite, so depending on the olivine content and strain-induced lattice-preferred orientation of olivine polymorphs, the 410 can be a sharp anisotropic boundary as well. The investigators will also use broadband P to SV/SH scattering signals collected by a global compilation of dense regional seismic arrays to better assess the isotropic/ anisotropic seismic structures near the 410. The results will be compared with new laboratory single-crystal high pressure-temperature sound velocity measurements. The ultimate goal of the proposed study is to estimate the lateral compositional variations in terms of olivine content and water concentration near 410 km depth, and the anisotropic velocity jumps across the 410 discontinuity. The majority of project funding will support an interdisciplinary team of students supervised by two early career PIs. This project will create unique opportunities for graduate and undergraduate students, especially underrepresented minority students, to participate in scientific research both on campus and at the state-of-the-art synchrotron facilities.

地幔是地球内最大的成分层，它不断地被与构造板块的运动、形成和破坏相关的热对流混合。从火山岩中可以清楚地看出，这种混合并没有产生均匀的地幔成分，然而，几乎没有观测限制可以绘制地幔内的成分变化图。该项目旨在测量地幔成分变化的范围，并绘制它们在全球范围内的空间分布图。重点是橄榄石矿物比例的变化，因为它是最丰富的地幔矿物，其局部丰度的变化会改变约 400 公里深度的地震反射边界的特性。该界面代表橄榄石晶体结构的变化，随着压力和温度随深度的增加而转变为瓦兹利石。确定橄榄石和瓦兹利石地震特性的实验室矿物物理实验将与密集区域阵列的地震数据分析相结合，以推断成分变化。除了估计橄榄石的含量外，该项目还将估计橄榄石中氢缺陷的丰度，橄榄石代表了地球深处潜在的地球化学水库。综合研究将为全球地幔混合和地幔产生火山活动的能力的空间变化提供新的见解。赠款资金将主要用于支持使用现代矿物物理学和地震方法的学生科学家的研究培训和教育。该项目将利用 410 公里不连续性的岩石学简单性，该不连续性是上地幔和过渡带之间的边界，研究地幔的体积和挥发性成分的空间变化。橄榄石-瓦兹利石转变是唯一可以导致全球观察到的410的相变。瓦兹利石的储水能力大约是橄榄石的五倍，结构水的存在可以深刻影响矿物的声速。因此，410 星等可以很好地估计地球内部 410 公里深度附近的橄榄石含量和水浓度。烃源岩中橄榄石含量高，产生岩浆的能力较差，因此橄榄石含量是地幔岩石学的良好指标。此外，橄榄石相对于瓦兹利石也具有强烈的各向异性，因此根据橄榄石含量和橄榄石多晶型物应变诱导的晶格择优取向，410也可以是尖锐的各向异性边界。研究人员还将使用由全球密集区域地震台阵收集的宽带 P 到 SV/SH 散射信号来更好地评估 410 附近的各向同性/各向异性地震结构。结果将与新的实验室单晶高压-温度声速测量。本研究的最终目标是估计 410 公里深度附近橄榄石含量和水浓度的横向成分变化，以及跨越 410 不连续面的各向异性速度跳跃。大部分项目资金将支持由两名早期职业 PI 监督的跨学科学生团队。该项目将为研究生和本科生，特别是代表性不足的少数族裔学生创造独特的机会，让他们在校园和最先进的同步加速器设施中参与科学研究。

项目成果

High pressure-temperature single-crystal elasticity of ringwoodite: Implications for detecting the 520 discontinuity and metastable ringwoodite at depths greater than 660 km

尖角橄榄石的高压-高温单晶弹性：对探测深度大于 660 km 的 520 不连续性和亚稳态尖角橄榄石的意义

• DOI: 10.1016/j.epsl.2021.117359
• 发表时间: 2022-02
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Zhou, Wen;Zhang, Jin S.;Huang, Quancheng;Lai, Xiaojing;Chen, Bin;Dera, Przemyslaw;Schmandt, Brandon
• 通讯作者: Schmandt, Brandon

Localized Anisotropy in the Mantle Transition Zone Due to Flow Through Slab Gaps

由于流过板状间隙而导致地幔过渡带的局部各向异性

• DOI: 10.1029/2021gl092712
• 发表时间: 2021-05
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Zhang, Han;Schmandt, Brandon;Zhang, Jin S.
• 通讯作者: Zhang, Jin S.

Constraining composition and temperature variations in the mantle transition zone

地幔过渡带的成分和温度变化的约束

• DOI: 10.1038/s41467-022-28709-7
• 发表时间: 2022-03
• 期刊: Nature Communications
• 影响因子: 16.6
• 作者: Zhou, Wen;Hao, Ming;Zhang, Jin S.;Chen, Bin;Wang, Ruijia;Schmandt, Brandon
• 通讯作者: Schmandt, Brandon

The Elastic Anisotropy Change Near the 410‐km Discontinuity: Predictions From Single‐Crystal Elasticity Measurements of Olivine and Wadsleyite

410公里不连续处附近的弹性各向异性变化：橄榄石和瓦兹利石单晶弹性测量的预测

• DOI: 10.1002/2017jb015339
• 发表时间: 2018-04-01
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Jin S. Zhang;J. Bass;B. Schm;t;t
• 通讯作者: t

A Single 520 km Discontinuity Beneath the Contiguous United States With Pyrolitic Seismic Properties

美国本土下方 520 公里的单一不连续面具有热解地震特性

• DOI: 10.1029/2022gl101300
• 发表时间: 2022-12
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Zhang, Han;Schmandt, Brandon;Zhou, Wen‐Yi;Zhang, Jin S.;Maguire, Ross
• 通讯作者: Maguire, Ross