Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 510, Issue -, Pages 45-52Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2019.01.006
Keywords
core; iron; melting; high pressure; inner core boundary; core-mantle boundary
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Funding
- JSPS Kakenhi grant [JP16H06023, JP16H01115, JP16H06285]
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The Earth's core is composed mainly of iron. Since the liquid core coexists with solid at the inner core boundary (ICB), the melting point of iron at 330 GPa offers a key constraint on core temperatures. However, previous results using a laser-heated diamond-anvil cell (DAC) have been largely inconsistent with each other, likely because of an intrinsic large temperature gradient and its temporal fluctuation. Here we employed an internal-resistance-heated DAC and determined the melting temperature of pure iron up to 290 GPa, for the first time above 200 GPa by static compression experiments. A small extrapolation of the present experimental results yields a melting point of 5500 +/- 220 K at the ICB, higher than 4850 +/- 200 K reported by previous laser-heated DAC by Boehler (1993) but is lower than 6230 500 K by Anzellini et al. (2013). Accounting for the melting temperature depression due to core-alloying elements, the upper bounds for the temperature at the ICB and the core mantle boundary (CMB) are estimated to be 5120 +/- 390 K and 3760 +/- 290 K, respectively. Such low present-day CMB temperature suggests that the lowermost mantle has avoided global melting, at least since early Proterozoic Eon. (C) 2019 Elsevier B.V. All rights reserved.
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