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

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、大洋板块和大陆板块的差异以及板块运动如何被下面的软流圈所适应等，至今仍不清楚。允许岩石圈板块运动的岩石圈板块下润滑的物理性质正在积极辩论。构造板块下的润滑层称为软流圈，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）和中央铁芯（约3400公里内半径）。我们知道，太阳系早期的岩石，被称为硅质岩，由铁和硅酸盐组成的复杂基质，然而，今天地球内部的铁核和硅酸盐地幔之间的这两种物质完全分离。这里提出的职业目标包括两个主要的重点方向，研究1）岩石圈和软流圈在海洋和大陆地幔和2）地球内部层的分化和形成在核心形成。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。利用新收集的海底地震仪数据和陆地仪器的地震工作将与旨在解决基本科学问题的实验室流体实验相结合。 这项建议的教育部分有两个方面，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，提高地质科学学生的定量技能。 一个新的少数民族计划在地质CSUN题为“地质经验为少数民族学生”（GEMS）将引导学生在整个本科学位的一部分，与辅导，同行支持，定期研讨会，参与研究活动，并在南非和海洋研究巡航实地工作的计划。还要求提供资金，以编制题为“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结合将确定岩石圈、软流圈的物理性质，以及大洋地幔和大陆地幔在这些性质上的差异。特别是工作将集中在软流圈测试以前的假设，这个不寻常的内层是由部分熔融，更高的水含量，或可能只是由于压力和温度的自然增加与地幔深度的综合影响的物理特性。本文提出用流体实验研究地球上地幔Saffman-Taylor不稳定性或粘性指进的增长和传播。将富含挥发性的羽流物质的指状物引入到耗尽的软流圈通道中所引起的粘度和浮力变化的组合可以解释在海洋和大陆环境中的几个观测结果，包括异常的表面火山活动和地震速度和重力异常的线性模式。指进波长、通道深度和流体粘度与地幔的比例关系将限制软流圈厚度和地幔流变学，在那里观测到海山，并进行了海底地震工作。另一套流体实验，提出了研究地球内部的分化周围的物理过程。地核的形成是地球历史上最大的分化事件，在地球形成的前30年中发生得非常快，但我们对这一巨大事件如何发生的物理学知之甚少。 由于铁和硅酸盐的物理性质存在巨大差异，以及模拟这些界面的计算挑战，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，漫画和地球化学研究。提出了一个研究方向，进行流体动力学实验，将一种新的介质的液体金属镓首次与传统的玉米糖浆流体相结合，以研究铁硅酸盐分异。按地球内部动力学尺度的流体实验将考虑适当的流变和温度制度，边界条件和液态金属不稳定性的时间尺度。下沉金属羽流的次级效应的发现包括尾随流体填充管道和上涌热化学羽流，这将考虑以下假设：核心形成事件启动了第一次上升的地幔羽流，并在整个地球内部将物质输送到过渡带和软流圈等区域。

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.