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

尽管板块构造理论早在40多年前就被地质界接受，但板块动力学的许多基本概念，如岩石圈的物理性质、成分、温度、物理尺寸、大洋和大陆板块的差异，以及板块运动如何被软流圈所容纳，至今仍不为人所知。岩石圈板块之下允许它们移动的润滑的物理性质正在激烈辩论。构造板块之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(约占地球外半径的一半)和中心铁核(约3400公里内半径)。我们知道太阳系早期的岩石，称为球粒陨石，由铁和硅酸盐组成的复杂基质，然而，今天的地球内部在铁核和硅酸盐地幔之间显示出这两种物质的完全分离。这里提出的职业目标包括两个主要的重点方向：1)大洋和大陆地幔中的岩石圈和软流圈；2)核心形成过程中地球内层的分异和形成。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。使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)吸引未被充分代表的少数族裔学生学习地质科学；2)通过在常见的地质问题中引入数学课来提高地球科学学生的量化技能。CSUN有一个新的少数民族地质学项目，名为《少数民族学生的地质体验》(GEMS)，该项目将指导学生完成本科学业，包括辅导、同行支持、定期研讨会、参与研究活动以及在南非和海洋研究巡航中的实地工作。还要求提供资金，以开发一门题为“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结合将确定岩石圈、软流层的物理性质，以及海洋和大陆地幔在这些性质上的差异。特别是，这项工作将集中在软流层的物理性质上，测试以前的假设，即这个不寻常的内层是由部分熔融、更高的水分组成，或者可能只是由于压力和温度随着地幔深度的自然增加而产生的综合影响。流体实验被用来研究Saffman-Taylor不稳定性或粘性指进在地球上地幔中的发展和传播。由于富含挥发性羽状物的指状物质进入枯竭的软流层通道而引起的粘度和浮力变化的组合，可以解释海洋和大陆环境中的几个观测结果，包括地表异常火山作用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对地幔的定标将限制软流圈的厚度和地幔流变性，在那里可以观测到海山和进行海底地震工作。另一组流体实验被提议用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，被证明在地球形成的前30年发生得非常快，但令人惊讶的是，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的巨大差异，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、卡通和地球化学研究。提出了首次将液态金属镓与传统的玉米糖浆流体相结合进行流体动力学实验研究铁硅酸盐分异的研究方向。根据地球内部动力学进行的流体实验将考虑液态金属不稳定性的适当的流变学和温度体系、边界条件和时间尺度。发现的下沉金属羽流的二次效应包括充满尾部流体的管道和上升式的热化学羽流，它们将考虑以下假设：核心形成事件引发第一批上升的地幔热柱，并将物质从地球内部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.