CAREER: Geodynamic Study of Earth's Mantle Asthenosphere and Core Formation

职业：地幔软流圈和地核形成的地球动力学研究

• 批准号: 1151941
• 负责人: Dayanthie Weeraratne
• 金额: $ 51.62万
• 依托单位: The University Corporation, Northridge
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-04-15 至 2017-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1151941&HistoricalAwards=false
• 关键词: CAREER; Geodynamic; Study; Earth; Mantle

Although plate tectonic theory was accepted in the geological community more than 40 yrs ago, many basic concepts of plate dynamics, such as the physical properties of the lithosphere, composition, temperature, physical dimensions, differences between oceanic and continental plates, and how plate motion is accommodated by the underlying asthenosphere is still unknown today. The physical nature of the lubrication beneath lithospheric plates that allows them to move is actively debated. The lubricating layer beneath tectonic plates known as the asthenosphere is part of a multi-layered structure of the interior of the Earth including the plates themselves, the silicate mantle (~half the Earth's outer radius), and the central iron core (~3400 km inner radius). We know that the early rocks of our solar system, known as chondrites, consisted of a complex matrix of iron and silicates, however, the Earth's interior today exhibits complete separation of these two substances between the iron core and silicate mantle. The career objectives proposed here encompass two main focus directions to study 1) the lithosphere and asthenosphere in oceanic and continental mantle and 2) differentiation and formation of the Earth's interior layers during core formation. This work will be carried out by methods that integrate seismology and geophysical fluid dynamics. Seismic work using newly collected ocean bottom seismometer data and land instruments, will be combined with laboratory fluid experiments designed to address fundamental scientific questions. The educational component of this proposal is two fold, 1) to attract underrepresented minority students to the geological sciences and 2) improve quantitative skills in geoscience students through introduction of math lessons through familiar geological problems. A new minority program in geology at CSUN titled 'Geological Experience for Minority Students' (GEMS) will guide students throughout their undergraduate degree as part of a program with mentoring, peer support, regular workshops, involvement in research activities, and field work in south Africa and marine research cruises. Funds are also requested to develop a new course titled "Mathematical Tools for Geologists", that will present mathematical concepts from the perspective of geological problems. The integration of fluid dynamic studies and seismic tomography methods will identify physical properties of the lithosphere, asthenosphere, and the difference in these properties between the oceanic and continental mantle. In particular the work will focus on the physical properties of the asthenosphere testing previous hypotheses that this unusual interior layer is composed of partial melt, higher water content, or may only be due to the combined effects of natural increases in pressure and temperature with depth in the mantle. Fluid experiments are proposed to study the growth and propagation of Saffman-Taylor instabilities or viscous fingering in the Earth's upper mantle. The combination of viscosity and buoyancy variations caused by the introduction of fingers of volatile rich plume material into a depleted asthenospheric channel may explain several observations in both oceanic and continental environments including anomalous surface volcanism and linear patterns of seismic velocity and gravity anomalies. Scaling of fingering wavelengths, channel depth, and fluid viscosities to the Earth's mantle will constrain asthenospheric thickness and mantle rheologies where seamounts are observed and ocean bottom seismic work has been done. Another set of fluid experiments are proposed to study the physical processes surrounding differentiation of the Earth's interior. The formation of the Earth's core is the biggest differentiation event in the Earth's history shown to have occurred very quickly in the first 30 My of Earth formation, yet we know surprisingly little about the physics of how this enormous event transpired. Because of the sharp difference in the physical properties of iron and silicates, and computational challenges in modeling these interfaces, our current understanding of this ancient event is limited to theoretical analysis, conceptual models, cartoons, and geochemical studies. A research direction is proposed to conduct fluid dynamic experiments that incorporate a new medium of liquid metal gallium combined for the first time with traditional corn syrup fluids to study iron-silicate differentiation. Fluid experiments scaled to Earth interior dynamics will consider appropriate rheological and temperature regimes, the boundary conditions, and time scales for liquid metal instabilities. Discovery of secondary effects from sinking metal plumes include trailing fluid filled conduits and upwelling thermo-chemical plumes that will consider the hypotheses that core forming events initiate the first rising mantle plumes and act to transport material throughout the Earth's interior to regions such as the Transition zone and asthenosphere.

尽管板块构造理论早在40多年前就被地质学界所接受，但板块动力学的许多基本概念，如岩石圈的物理性质、组成、温度、物理尺寸、海洋和大陆板块之间的差异，以及板块运动如何被底层软流圈调节，至今仍不为人所知。岩石圈板块下润滑的物理性质使它们能够移动，这一问题一直备受争议。被称为软流层的构造板块下的润滑层是地球内部多层结构的一部分，包括板块本身，硅酸盐地幔（约地球外半径的一半）和中央铁核（约3400公里内半径）。我们知道太阳系的早期岩石，即球粒陨石，是由铁和硅酸盐的复杂基质组成的。然而，今天地球内部的铁核和硅酸盐地幔之间完全分离了这两种物质。本文提出的职业目标主要包括两个重点研究方向：1)海洋和大陆地幔中的岩石圈和软流圈；2)地核形成过程中地球内层的分化和形成。这项工作将采用地震学和地球物理流体动力学相结合的方法进行。地震工作使用新收集的海底地震仪数据和陆地仪器，将与实验室流体实验相结合，旨在解决基本的科学问题。该提案的教育内容有两个方面，1)吸引代表性不足的少数民族学生学习地质科学，2)通过介绍熟悉的地质问题的数学课程来提高地球科学学生的定量技能。CSUN的一个名为“少数族裔学生地质体验”（GEMS）的新少数族裔地质学项目将指导学生完成整个本科学位，作为该项目的一部分，该项目包括指导、同伴支持、定期研讨会、参与研究活动、在南非的实地工作和海洋研究巡航。还要求提供经费，以编制一门题为“地质学家的数学工具”的新课程，从地质问题的角度介绍数学概念。流体动力学研究和地震层析成像方法的整合将确定岩石圈、软流圈的物理性质，以及海洋和大陆地幔之间这些性质的差异。特别地，这项工作将集中在软流圈的物理特性上，测试先前的假设，即这个不寻常的内层是由部分熔融、更高的含水量组成的，或者可能只是由于地幔深度自然增加的压力和温度的综合影响。提出了流体实验来研究地球上地幔中Saffman-Taylor不稳定性或粘性指状的生长和传播。由挥发性丰富的羽流物质引入枯竭的软流圈通道所引起的黏度和浮力变化的组合，可以解释海洋和大陆环境中的一些观测结果，包括地表火山活动的异常以及地震速度和重力异常的线性模式。对指进波长、通道深度和地幔流体粘度的标度将限制软流圈的厚度和地幔流变，在这些地方可以观测到海底山，并进行海底地震工作。提出了另一套流体实验来研究围绕地球内部分化的物理过程。地核的形成是地球历史上最大的分化事件，发生在地球形成的前30万年，发生得非常快，然而我们对这一巨大事件如何发生的物理学知之甚少。由于铁和硅酸盐在物理性质上的巨大差异，以及对这些界面建模的计算挑战，我们目前对这一古老事件的理解仅限于理论分析、概念模型、卡通和地球化学研究。提出了一个研究方向，即首次将液态金属镓与传统玉米糖浆流体结合的新介质进行流体动力学实验，研究铁硅酸盐的分化。以地球内部动力学为尺度的流体实验将考虑适当的流变学和温度制度、边界条件和液态金属不稳定性的时间尺度。从下沉的金属羽流中发现的次要影响包括尾部充满流体的管道和上涌的热化学羽流，它们将考虑地核形成事件引发第一次上升的地幔羽流的假设，并将物质运输到整个地球内部的区域，如过渡带和软流圈。