Melting curve of iron to 290 GPa determined in a resistance-heated diamond-anvil cell
Melting curve of iron to 290 GPa determined in a resistance-heated diamond-anvil cell
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DOI：
10.1016/j.epsl.2019.01.006
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发表时间：
2018-12
影响因子：
5.3
通讯作者：
R. Sinmyo;K. Hirose;Y. Ohishi
中科院分区：
文献类型：
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作者：
R. Sinmyo;K. Hirose;Y. Ohishi
地核主要由铁组成。由于液体核心与固体在内核边界 (ICB) 处共存，因此 330 GPa 的铁熔点对核心温度提供了关键限制。然而，之前使用激光加热金刚石砧座（DAC）得到的结果在很大程度上彼此不一致，这可能是因为固有的大温度梯度及其时间波动。在这里，我们采用内阻加热DAC，并通过静态压缩实验确定了纯铁的熔化温度高达290 GPa，首次超过200 GPa。对当前实验结果进行小幅外推，ICB 处的熔点为 5500 ± 220 K，高于 Boehler (1993) 先前激光加热 DAC 报告的 4850 ± 200 K，但低于 Anzellini 等人的 6230 ± 500 K。 （2013）。考虑到核心合金元素导致的熔化温度降低，ICB 和核心-地幔边界 (CMB) 的温度上限估计分别为 5120 ± 390 K 和 3760 ± 290 K。目前如此低的宇宙微波背景温度表明，至少自元古代早期以来，最低地幔已经避免了全球融化。
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.