DI010-04
High-Pressure Melting of Fe-Ni-Si: Insights from Complementary Experimental Approaches
Wednesday, 9 December 2020: 20:42
Virtual
Vasilije V Dobrosavljevic1, Dongzhou Zhang2, Wolfgang Sturhahn1, Jiyong Zhao3, Thomas Toellner4, Stella Chariton5, Vitali Prakapenka5 and Jennifer M Jackson1, (1)California Institute of Technology, Seismological Laboratory, Pasadena, CA, United States, (2)University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, Honolulu, HI, United States, (3)Argonne National Laboratory, Argonne, IL, United States, (4)Argonne National Laboratory, Advanced Photon Source, Argonne, IL, United States, (5)University of Chicago, Center for Advanced Radiation Sources, Chicago, IL, United States
Abstract:
The expected temperature profile of Earth’s core, often constrained through the high-pressure melting of core-relevant materials, holds significant implications for major geophysical phenomena, such as the age of the inner core and geodynamo, the magnitude of heat flow through the core-mantle boundary over geologic time, and the complex structure and phase relations of the lowermost mantle (Dobrosavljevic et al. 2019,
Minerals). However, two major sources of uncertainty contribute to the persistently large error bars on the temperatures of the inner-core and core-mantle boundaries. For one, relatively few studies have investigated the influence of light elements on the melting curves of the inferred Fe-Ni compositional system of the core. At the same time, the melting curve of pure iron remains controversial due to discrepancies across experimental techniques and melt-detection diagnostics.
In this work, we conduct laser-heated diamond anvil cell (DAC) experiments with a combination of complementary melt-detection techniques to study the high-pressure melting of Fe0.8Ni0.1Si0.1, a candidate core composition. At beamline 3-ID-B of the Advanced Photon Source (APS) of Argonne National Laboratory, we used synchrotron Mössbauer spectroscopy to probe the atomic dynamics of the iron nucleus across the solid-liquid phase boundary (Jackson et al. 2013, EPSL; Zhang et al. 2016, EPSL). At beamline 13-ID-D of the APS, using samples from the same bulk material under the same DAC loading conditions, we conducted a series of X-ray diffraction experiments to detect the onset of liquid diffuse scattering. We additionally investigated other commonly used melt diagnostics, such as discontinuities in the laser power – temperature profiles, plateaus in the volume – temperature profiles, and the onset of recrystallization. Through the richness of these data sets, we examine the effects of silicon on the Fe-Ni phase diagram, and in doing so demonstrate the advantages of combining complementary experimental techniques in investigations of melting under extreme conditions.
