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

OCE-0752166智力成果：本项目将研究地球内部的一个基本性质-地幔位温、地震速度和衰减与大洋中脊玄武岩岩石学之间的关系。特别是，我们将检验一个假设，即地幔位温的变化存在沿着全球洋中脊系统的轴，高达200 ℃。如果这是真的，这种热变化应该产生一个可观察到的地震特征，因为温度升高导致剪切波速度降低和剪切波衰减增加。大洋中脊是板块分离的分界线，在此之下，地幔发生熔融和上涌。原则上，岩石学对洋脊顶部下地幔温度的估计应该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大幅度变化的结果这一解释，并将更清楚地说明岩石学和地震数据的正确解释，这些数据可以应用于山脊系统以外的地震数据，并随着时间的推移利用来自较老岩石的数据。这将使地球科学家对地震学和海底岩石样品岩石学分析这两个最基本工具的数据解释更有信心，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。将使用几个全球地震剪切波速度模型来限制沿着整个洋中脊系统的三维波速变化。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，将有助于区分稳健和可重复的特征和仅受弱约束的特征。全球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。最近在实验室测量剪切速度和衰减方面取得的进展，将使我们能够对地震学观测到的温度和成分方面的数量作出比以前更严格的解释。通过全球PetDB数据库的存在，以及过去几年收集的大量新数据集，岩石学分析将相对于以前的工作得到增强，这将大大提高全球覆盖范围。将使用新的和改进的程序来纠正这些数据的化学分馏和实验室间偏倚。由此产生的数据集，然后可以用来估计温度沿着每个脊段，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。一种新的方法也将被用来检查这些数据集在频域中，以调查在不同的长度scales.Broader影响的相关性的可能性：这个项目本质上是跨学科的，并利用自然交叉的推断，可以从地震学和岩石学数据。无论结果如何，这项工作的影响是深远的。现今整个地球的温度和成分分布与地幔流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允许对地球的热历史进行反向预测。此外，将在解决围绕正确解释岩石学和地震学数据的未决争议方面取得进展。该项目为一名研究生提供支持，她将在职业生涯的早期阶段从参与跨学科项目中受益。波士顿大学本科生的参与将向未来的研究生介绍研究环境。该项目为一名早期职业女性科学家（道尔顿）提供资金，以获得与研究生和另一学科（朗缪尔）的知名科学家一起工作的经验。

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).