Collaborative Research: Investigations of the relationship between seismological and petrological constraints on upper-mantle temperature and composition

合作研究：地震学和岩石学约束对上地幔温度和成分之间关系的研究

• 批准号: 0752281
• 负责人: Charles Langmuir
• 金额: $ 14.31万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2011-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0752281&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigations; relationship; between

OCE-0752166Intellectual Merit: This project will investigate a fundamental property of the Earth's interior - the relationship between mantle potential temperature, seismic velocity and attenuation, and the petrology of mid-ocean ridge basalts (MORBs). In particular, we will test a hypothesis that variations in mantle potential temperature exist along the axis of the global mid-ocean ridge system, of up to 200 C. If this is true, such thermal variations should produce an observable seismic signature, as increased temperature leads to slower shear-wave velocities and to higher shear-wave attenuation. The mid-ocean ridge marks the boundary between tectonic plates at which the plates are separating, and beneath which the Earth's mantle undergoes melting and upwelling. In principal, petrological estimates of temperature within the mantle beneath the ridge crests should agree with seismological estimates of temperature. Agreement of the two approaches will test the interpretation that MORB sodium and iron content is the result of large variations in mantle potential temperature, and will provide greater clarity concerning the proper interpretation of both petrological and seismic data that can be applied beyond the ridge system using the seismic data, and through time making use of data from older rocks. This will provide greater confidence for the interpretation of data from two of the most fundamental tools for Earth scientists, seismology and petrological analysis of seafloor rock samples.The proposed work consists of separate and joint examinations of seismological and petrological datasets. Several global seismic shear-wave velocity models will be used to constrain three-dimensional variations in wave speed along the entire mid-ocean ridge system. Consideration of velocity models developed by different groups using a range of seismic data and diverse techniques will help distinguish robust and reproducible features from those that are only weakly constrained. Global attenuation models will be used to assist the interpretation of the velocity anomalies, as the sensitivity of attenuation to factors such as temperature and composition complements the sensitivity of velocity. Recent progress in laboratory measurements of shear velocity and attenuation will permit a more rigorous interpretation of the seismologically observed quantities in terms of temperature and composition than has previously been possible. The petrological analysis will be enhanced relative to previous work by the existence of the global PetDB database, and extensive new datasets collected over the past several years that will substantially enhance the global coverage. New and improved procedures will be used to correct these data for chemical fractionation and inter-laboratory bias. The resulting dataset can then be used to estimate temperature along each ridge segment and to evaluate potential compositional variations. The combined analysis of the petrological and seismological datasets involves comparison of the two sets of data to look for correlations and intriguing patterns. A novel approach will be used also examine these datasets within the frequency domain to investigate the possibility of correlations at various length scales.Broader Impacts: This project is inherently cross-disciplinary and takes advantage of a natural intersection in the inferences that can be made from seismological and petrological data. Regardless of the result, the implications of this work are far-reaching. The present-day distribution of temperature and composition throughout the Earth is strongly coupled to mantle flow and the tectonic processes that are observable at theEarth's surface. Understanding the relationship between temperature, composition, and petrology will allow back-projections of the Earth's thermal history. In addition, progress will be made toward resolving outstanding controversies surrounding the proper interpretation of petrological and seismological data. This project provides support for one graduate student who will benefit from involvement in an interdisciplinary project at an early stage in her career. Involvement of an undergraduate at Boston University will introduce a potential future graduate student to the research environment. The project provides funding for an early-career female scientist (Dalton) to gain experience working with both the graduate student and an established scientist from another discipline (Langmuir).

OCE-0752166智力成果：该项目将研究地球内部的基本属性 - 地幔潜在温度、地震速度和衰减之间的关系，以及洋中脊玄武岩 (MORB) 的岩石学。特别是，我们将检验一个假设，即沿全球大洋中脊系统的轴线存在地幔潜在温度的变化，最高可达 200 摄氏度。如果这是真的，这种热变化应该会产生可观测的地震特征，因为温度升高会导致剪切波速度变慢和剪切波衰减更高。大洋中脊标志着构造板块之间的边界，板块在此处分离，地幔在其下方经历融化和上涌。原则上，岩石学对脊顶下方地幔内温度的估计应与地震学对温度的估计一致。这两种方法的一致性将检验 MORB 钠和铁含量是地幔潜在温度巨大变化的结果的解释，并将为岩石学和地震数据的正确解释提供更清晰的信息，这些数据可以使用地震数据应用于山脊系统之外，并随着时间的推移利用来自较古老岩石的数据。这将为地球科学家的两个最基本工具——地震学和海底岩石样本的岩石学分析——的数据解释提供更大的信心。拟议的工作包括对地震学和岩石学数据集的单独和联合检查。多个全球地震剪切波速度模型将用于约束整个洋中脊系统波速的三维变化。考虑不同小组使用一系列地震数据和不同技术开发的速度模型将有助于区分稳健且可重复的特征与仅弱约束的特征。全局衰减模型将用于协助解释速度异常，因为衰减对温度和成分等因素的敏感性补充了速度的敏感性。剪切速度和衰减的实验室测量的最新进展将允许对温度和成分方面的地震观测量进行比以前更严格的解释。全球 PetDB 数据库的存在以及过去几年收集的大量新数据集将大大增强全球覆盖范围，相对于以前的工作，岩石学分析将得到加强。新的和改进的程序将用于纠正这些数据的化学分馏和实验室间偏差。然后，所得数据集可用于估计沿每个山脊段的温度并评估潜在的成分变化。岩石学和地震学数据集的综合分析包括比较两组数据，以寻找相关性和有趣的模式。还将使用一种新颖的方法在频域内检查这些数据集，以研究不同长度尺度下相关性的可能性。更广泛的影响：该项目本质上是跨学科的，并利用了地震学和岩石学数据推论中的自然交叉点。无论结果如何，这项工作的影响都是深远的。目前整个地球的温度和成分分布与地幔流和地球表面可观测到的构造过程密切相关。了解温度、成分和岩石学之间的关系将有助于对地球的热历史进行反投影。此外，在解决围​​绕正确解释岩石学和地震学数据的悬而未决的争议方面将取得进展。该项目为一名研究生提供支持，她将受益于在职业生涯早期参与跨学科项目。波士顿大学本科生的参与将向未来潜在的研究生介绍研究环境。该项目为一名职业生涯早期的女科学家（道尔顿）提供资金，以获得与研究生和另一学科的知名科学家（朗缪尔）合作的经验。