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

约书亚罗素博士已被授予美国国家科学基金会博士后奖学金，在布朗大学科琳道尔顿博士的指导下开展研究和教育活动。板块构造学描述了覆盖在活跃对流的软流圈上的地球刚性板块（岩石圈）的运动，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%，由于其地质简单，为板块构造过程提供了一个清晰的窗口。然而，对板块构造的基本方面仍然知之甚少，例如定义板块底部的化学和物理特征以及它们如何随板块年龄而变化。该项目旨在通过将太平洋下地幔的高分辨率地震成像与最近对地球地幔中最丰富的矿物橄榄石的物理性质的实验限制相结合，调和关于海洋岩石圈-软流圈边界（LAB）的起源和演变的相互竞争的假设。教育计划包括：1）为当地小学制定和提供地球科学课程计划，2）通过暑期研究项目指导本科生，3）在布朗大学组织关于板块构造和实验室的阅读研讨会。滞弹性和各向异性结构的上地幔的细节。该项目将利用太平洋五个OBS阵列的面波数据，海底年龄从~6 Ma到~120 Ma不等，以建立每个地点的剪切速度、剪切衰减和地震各向异性模型。将开发一种新的技术，用于在存在洛夫波泛音干扰的情况下恢复速度结构，该技术将调和径向各向异性的相互冲突的模型。在每个站点的剪切速度和衰减的地震观测将直接比较相应的实验室预测通过一个新开发的贝叶斯框架，以产生估计地幔温度，粒度和熔体分数和它们的年龄依赖性在海洋上地幔。该项目是第一次努力整合地震规模和实验室规模的地幔滞弹性在几个高分辨率的OBS阵列在太平洋盆地的约束。除了阐明控制LAB及其假设年龄依赖性的机制外，这项工作还将为海洋上地幔的热力学状态提供新的约束，这是理解更广泛行星演化的关键。该奖学金获得了地球科学部地球物理学项目的部分资助。该奖项反映了NSF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.