MR33D-03
Temperature of Earth's Deep Interior Constrained from Melting of Fe and Fe0.9Ni0.1 at High Pressures

Wednesday, 16 December 2015: 14:10
301 (Moscone South)
Dongzhou Zhang1, Jennifer M Jackson2, Jiyong Zhao3, Wolfgang Sturhahn2, Esen Ercan Alp4, Michael Y. Hu5, Thomas Toellner5 and Caitlin A Murphy6, (1)University of Hawaii at Manoa, Honolulu, HI, United States, (2)California Institute of Technology, Pasadena, CA, United States, (3)Advanced Photon Source, Argonne National Laboratory, Argonne, IL, United States, (4)Argonne National Laboratory, Advanced Photon Source, Argonne, IL, United States, (5)Argonne National Laboratory, Argonne, IL, United States, (6)Geophysical Laboratory, Washington Dc, DC, United States
Abstract:
The melting points of fcc- and hcp-structured Fe0.9Ni0.1 and Fe have been measured up to Mbar pressure. We use laser heated diamond anvil cells, time-resolved synchrotron Mössbauer spectroscopy, x-ray diffraction and a recently developed fast temperature readout spectrometer to carry out these measurements. X-ray photons at 57Fe's resonant energy with 1 meV bandwidth are focused on the sample in a laser heated diamond anvil cell, and when melting occurs, the characteristic Mössbauer signal abruptly decreases. Thus, time-resolved Mössbauer spectroscopy provides an excellent diagnostic for the first melt formed in the sample chamber. The thermal contributions of pressure of Fe0.9Ni0.1 and Fe have been constrained by combining nuclear resonant inelastic scattering and high temperature X-ray diffraction measurements. We find that the melting curve of Fe is systematically higher than the melting curve of Fe0.9Ni0.1, while the 1-σ temperature uncertainties of both melting curves overlap. The pressure dependencies of the melting temperature of fcc-structured Fe and Fe0.9Ni0.1 are measured, and the best-fit melting curves are located in the region bounded by previous studies. Our results may help reach a consensus on the high pressure melting curves of Fe and Fe-Ni alloys. We calculate the fcc-hcp-liquid triple points of Fe0.9Ni0.1and Fe, complemented by experiments with Mössbauer spectroscopy. The upper bound of Earth's inner core-outer core boundary temperature is estimated from our results, and the upper bound of the temperature at Earth’s core-mantle boundary is computed with an adiabatic model. We discuss the implications of these temperatures on the phase relations of deep Earth materials.

References:

Murphy, C.A., J.M. Jackson, W. Sturhahn, and B. Chen (2011): Melting and thermal pressure of hcp-Fe from the phonon density of states, Phys. Earth Planet. Int., 188, 114-120

Jackson, J.M., W. Sturhahn, M. Lerche, J. Zhao, T.S. Toellner, E.E. Alp, S.V. Sinogeikin, J.D. Bass, C.A. Murphy, and J.K. Wicks (2013): Melting of compressed iron by monitoring atomic dynamics, EPSL, 362, 143-150

Zhang, D., J.M. Jackson, J. Zhao, W. Sturhahn, E.E. Alp, T.S. Toellner, and M. Hu (2015): Fast temperature spectrometer for samples under extreme conditions. Review of Scientific Instruments, 86, 013105

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