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.
