EAR-PF Discerning the nature of the oceanic lithosphere-asthenosphere boundary through integration of seismological-scale and laboratory-scale observations

Joshua Russell博士获得美国国家科学基金会EAR博士后奖学金，在布朗大学Colleen Dalton博士的指导下开展研究和教育活动。板块构造学描述了地球上的刚性板块（岩石圈）的运动，这些板块覆盖在积极对流的软流圈上，为理解地球的动力学和演化提供了一个全面的框架。海洋盆地约占地球表面的70%，由于其地质的简单性，为板块构造过程提供了一个清晰的窗口。然而，人们对板块构造的基本方面仍然知之甚少，比如确定板块底部的化学和物理特征，以及它们如何随着板块年龄的变化而变化。该项目旨在通过整合太平洋下地幔的高分辨率地震成像和最近对橄榄石（地幔中最丰富的矿物）物理性质的实验限制，来调和关于海洋岩石圈-软流圈边界（LAB）起源和演化的相互矛盾的假设。该教育计划包括：1)为当地小学课堂制定并提供地球科学课程计划；2)通过暑期研究项目指导一名本科生；3)在布朗大学组织一次关于板块构造和实验室的阅读研讨会。近年来，太平洋海底地震仪（OBS）阵列的扩散为详细表征上地幔的大尺度弹性、非弹性和各向异性结构提供了前所未有的机会。该项目将利用太平洋5个OBS阵列的表面波数据，海底年龄从~6 Ma到~120 Ma不等，在每个地点建立剪切速度、剪切衰减和地震各向异性的模型。将开发一种新的技术，用于恢复存在Love-wave泛音干涉的速度结构，该技术将调和径向各向异性的冲突模型。每个地点的剪切速度和衰减的地震观测将直接与通过新开发的贝叶斯框架的相应实验室预测进行比较，以产生对海洋上地幔的地幔温度，粒度和熔融分数及其年龄依赖性的估计。该项目首次将太平洋盆地几个高分辨率OBS阵列的地震尺度和实验室尺度的地幔非弹性约束结合起来。除了阐明控制LAB的机制及其假设的年龄依赖性外，这项工作将为海洋上地幔的热力学状态提供新的约束，这是理解更广泛的行星演化的关键。该奖学金的部分资金来自地球科学部的地球物理项目。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. Joshua Russell has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education activities under the mentorship of Dr. Colleen Dalton at Brown University. Plate tectonics describes the motion of Earth’s rigid plates (the lithosphere) that overlie the actively convecting asthenosphere, providing a comprehensive framework for understanding the dynamics and evolution of the planet. The ocean basins comprise approximately 70% of Earth’s surface and, due to their geologic simplicity, provide a clear window into plate tectonic processes. Yet, fundamental aspects of plate tectonics remain poorly understood, such as the chemical and physical characteristics that define the base of the plate and how they vary with plate age. This project aims to reconcile competing hypotheses for the origin and evolution of the oceanic lithosphere-asthenosphere boundary (LAB) by integrating high-resolution seismic imaging of the mantle beneath the Pacific Ocean with recent experimental constraints on the physical properties of olivine, the most abundant mineral in Earth’s mantle. The education plan consists of 1) developing and delivering an Earth science lesson plan to local elementary school classrooms, 2) mentoring an undergraduate student through a summer research project, and 3) organizing a reading seminar at Brown University on plate tectonics and the LAB.Recent proliferation of ocean-bottom seismometer (OBS) arrays in the Pacific offers an unprecedented opportunity to characterize the large-scale elastic, anelastic, and anisotropic structure of the upper mantle in detail. This project will utilize surface-wave data from five OBS arrays in the Pacific, ranging in seafloor age from ~6 Ma to ~120 Ma, to develop models of shear velocity, shear attenuation, and seismic anisotropy at each site. A new technique will be developed for recovering velocity structure in the presence of Love-wave overtone interference that will reconcile conflicting models of radial anisotropy. Seismic observations of shear velocity and attenuation at each site will be directly compared with corresponding laboratory predictions via a newly developed Bayesian framework to yield estimates of mantle temperature, grain size, and melt fraction and their age dependence in the oceanic upper mantle. This project represents a first effort to integrate seismological-scale and laboratory-scale constraints on mantle anelasticity across several high-resolution OBS arrays in the Pacific basin. In addition to illuminating the mechanism(s) controlling the LAB and its hypothesized age dependence, this work will provide new constraints on the thermodynamic state of the oceanic upper mantle that is key for understanding broader planetary evolution. This fellowship received partial funding from the Geophysics program in the Earth Science division.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.