The Earth and Planets Laboratory hosts free weekly scientific seminars most Mondays and Thursdays. The popular seminar series covers the broad range of topics studied on our campus and are presented by both guest speakers and Carnegie scientists.
Note: These seminars are designed for a scientific audience and have limited space, so we are not advertising the Zoom links publically. However, you're still welcome to join! Just email Alycia Alexander (adalexander@carnegiescience.
- Monday, June 6, 2022, at 11:00 a.m. (virtual seminar)
Innocent Ezenwa, Earth and Planets Laboratory
Title: High-Pressure Melting Curve of Fe: Explored by Inter-Metallic Fast Diffusion Technique
Abstract: The global magnetic field is generated by the convective motion in the liquid outer core. The high-pressure melting curve of Fe is crucial in assessing planetary core temperature at the inner core boundary (ICB). Although the temperature at the ICB would be adjusted to account for the effects of the light alloying elements, the melting temperature of pure Fe places an upper bound at the ICB and it is an important fixed point in the thermal profile of the planetary core. Here, we present a new method to precisely determine the melting temperature in the multi-anvil press. We established a new melting criterion to detect melting by characterizing the interface behavior. It is generally known that diffusion in disordered materials is faster than in the respective crystalline phases. Hence, a change in the diffusion processes can be used as a criterion to detect melting. In this study, we measured the melting temperature of Fe as a function of pressure up to 22 GPa using this “inter-metallic fast diffusion” method. Our data place a tighter constraint in the melting curve of Fe measured in the large-volume press.
Host: Yingwei Fei
- Monday, June 6, 2022, at 11:30 a.m. (virtual seminar)
Francesca Miozzi-Ferrini, Earth and Planets Laboratory
Title: Application of the double capsule technique in multi-anvil apparatuses for the synthesis of COH fluids in equilibrium with diamonds
Abstract: In recent years efforts have been made to investigate the solubility of graphitic carbon in aqueous fluids at high pressure, high-temperature conditions. Experiments on graphite-and amorphous carbon-saturated fluids, with or without other mineral phases (e.g. quartz/coesite, forsterite + enstatite) indicate the reliability of conventional thermodynamic models in the pure C–O–H system with ordered graphite. However, they also show that the same models fail to reproduce fluid speciation in more complex systems bearing silicates or disordered graphite. The same experimental strategy and analytical methods are used here to experimentally investigate the solubility of carbon in aqueous fluids at P–T conditions where diamond is stable. We conducted multi-anvil experiments at P = 5 GPa and T = 950 ˚C, corresponding to conditions in a relatively cold cratonic lithosphere, employing the double capsule technique to synthesize COH fluids in equilibrium with synthetic diamonds at redox conditions close to EMOD. These fluids were analyzed to retrieve the absolute amount of CO 2 formed during the oxidative dissolution of diamond in pure water. Our preliminary results show that: i) the double capsule technique can be successfully applied to multi-anvil experiments; ii) neither nanosize diamonds nor chloride affected the solubility of the diamonds. In marked contrast, the solubility of diamonds was enhanced by almost one order of magnitude in the presence of SiO 2 with respect to the pure system and the speciation calculated with conventional thermodynamic models.
- Monday, June 13, 2022, at 11:00 a.m. (virtual seminar)
Jennifer Jackson, Caltech
Title: Ultralow seismic velocity zones at Earth's core-mantle boundary
Abstract: The boundary layer separating the iron-dominant liquid outer core from the silicate-rich mantle is a region of great complexity, where extreme contrasts in material properties promote the persistence of multiscale structural heterogeneities, as evidenced through seismic observations. The thermochemical variations at the lowermost mantle play an important role in the evolutionary history of the Earth through the regulation of heat flow and influence the dynamics of both the mantle and the core. Despite the significance of this region for Earth’s evolution, many open questions remain regarding the characteristics, origins, and dynamic interactions of the observed heterogeneities, such as large thermochemical piles, regions of ultralow seismic velocities, and subducted former oceanic material [e.g., 1]. As individual observational studies of such features and experimental investigations into candidate compositions continue to develop, a synthesis of results from seismology, geodynamic modeling, and mineral physics provides quantitative and systematic avenues for revealing new insights into this complex region.
Host: Anne Pommier
- Tuesday, June 21, 2022, at 11:00 a.m. (hybrid seminar)
Cian Wilson, Earth and Planets Laboratory
Title: Consistent Thermo- and Geo-Dynamics: Applications to Mantle Convection
Abstract: The integration of computational thermodynamics and geodynamics is critical for a wide range of problems from mantle convection with consistent phase changes, to open system reactive transport during fluid/magma migration. These problems are strongly coupled, non-linear, involve large numbers of variables, and remain some of the outstanding computational challenges in solid-earth science. To address these challenges requires flexible modeling software that allows the user to control the degree of complexity in both thermodynamic and geodynamic models.
Advances in computational software over the last decade have provided a range of numerical libraries that allow the application of symbolic computational mathematics to geodynamics. These libraries turn simple problem descriptions into problem-specific, high-performance code. Importantly for highly coupled problems, the use of symbolic calculus allows the automatic calculation of derivatives for use in the nonlinear solver. ThermoCodeGen, part of the larger ENKI project for thermodynamic modeling, applies these principles to thermodynamic problems, automatically generating the derivatives of free energy models to supply consistent thermodynamic parameters for use in geodynamic models. I will present results applying ThermoCodeGen to mantle convection problems, demonstrating a range of complexities in both the geodynamic problem formulation and the degree of thermodynamic consistency.
Host: Peter van Keken
- Monday, June 27, 2022, at 11:00 a.m. (hybrid seminar)
Ningli Zhao, Earth and Planets Laboratory
Host: Peter van Keken
- Monday, June 27, 2022, at 11:30 a.m. (hybrid seminar)
Nate Sime, Earth and Planets Laboratory
Host: Peter van Keken
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