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

智力优势：这个项目将研究地球内部的一个基本性质-地幔潜在温度、地震速度和衰减之间的关系，以及大洋中脊玄武岩(MORBs)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高达200摄氏度的地幔潜在温度变化。如果这是真的，这种温度变化应该产生可观察到的地震信号，因为温度升高导致剪切波速度变慢，剪切波衰减增加。大洋中脊标志着两个板块分离的构造板块之间的边界，在该板块下，地球地幔经历了融化和上涌。原则上，岩石学对山脊下地幔内温度的估计应该与地震学对温度的估计相一致。这两种方法的一致将检验MORB钠和铁含量是地幔潜在温度巨大变化的结果的解释，并将提供更大的清晰度，以便正确解释岩石学和地震数据，这些数据可以利用地震数据应用于海脊系统之外，并随着时间的推移利用来自较老岩石的数据。这将为地球科学家从地震学和海底岩石样本的岩石学分析这两个最基本的工具中解释数据提供更大的信心。拟议的工作包括对地震学和岩石学数据集进行单独和联合检查。几个全球地震横波速度模型将被用来约束整个大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，将有助于区分健壮和可重现的特征与那些仅受弱约束的特征。全球衰减模型将用于辅助解释速度异常，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。实验室测量剪切速度和衰减的最新进展将使地震观测量在温度和成分方面得到比以前可能的更严格的解释。由于全球PetDB数据库的存在，以及过去几年收集的大量新数据集的存在，岩石学分析将比以前的工作得到加强，这将大大提高全球覆盖面。将使用新的和改进的程序来校正这些数据，以消除化学分馏和实验室间的偏差。然后，生成的数据集可以用来估计每个脊线段的温度，并评估潜在的成分变化。对岩石学和地震学数据集的综合分析包括对两组数据进行比较，以寻找相关性和有趣的模式。还将使用一种新的方法在频域内检查这些数据集，以调查不同长度尺度上的相关性的可能性。广泛的影响：该项目本质上是跨学科的，并利用了可以从地震学和岩石学数据进行推断的自然交集。无论结果如何，这项工作的影响都是深远的。现今地球上温度和成分的分布与地幔流动和在地球表面可观察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热史的反向预测。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。这个项目为一名研究生提供支持，她将在职业生涯的早期阶段参与一个跨学科的项目，从而受益。波士顿大学本科生的参与将把潜在的未来研究生引入研究环境。该项目为一名职业生涯早期的女科学家(道尔顿)提供资金，以获得与研究生和来自另一学科(朗缪尔)的知名科学家合作的经验。

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).