Melting of compressed iron-alloys using a multi-technique approach

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Accurate estimates of the temperature range of Earth’s core are essential for understanding major processes like inner core crystallization, magnetic field generation, and heat flow through the core-mantle boundary, as well as the compositions, phase relations, and dynamics of complex multiscale structures in Earth's lowermost mantle. With its location several thousand kilometers below the Earth's surface, determining its exact composition and temperature profile is a challenge. Laboratory experiments, theory, seismic observations are used to infer core characteristics. Seismological and cosmochemical observations indicate that Earth's core consists of a solid inner region surrounded by a liquid outer core, with iron as the main compositional constituent, but a lighter element is needed in combination with iron to explain the density of the core. This project explores the possibility of nickel or silicon as elements of the the core. Outreach activities and benefits to society include the strong engagement of the PI and involved graduate student in Caltech’s Seismological Laboratory’s Earthquake Fellows Program, a partnership with the Dr. Lucy Jones Center for Science and Society. This program is part of a multi-pronged program with the goal of bringing geophysical science to the wider community in Southern California, while creating an opportunity for communities that are historically marginalized and underrepresented in the sciences to develop STEM skills. Many studies have suggested silicon as a candidate light element for the core of the Earth to explain the density deficit if one assumes a core that is purely made of iron. However, the effect of silicon on the melting temperatures of core materials and the thermal profile of the core is poorly understood due to disagreements among melt detection techniques, uncertainties in sample pressure evolution during heating, and sparsity of studies investigating the combined effects of nickel and silicon on the phase diagram of iron. This project takes the multi-technique approach developed by this team of researchers for detecting melting of iron-alloys at high pressures that combines results from two independent in-situ probes: synchrotron Mössbauer spectroscopy, sensitive to dynamics of solid-bound iron, and x-ray diffraction, sensitive to long-range crystalline order. They will apply the new multi-technique method of melt detection to Fe, Fe-Ni, and Fe-Ni-Si at pressures equivalent to those in Earth’s core, placing tighter constraints on the temperature of Earth’s core. 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.