Strength of iron at core pressures and evidence for a weak Earth's inner core
Strength of iron at core pressures and evidence for a weak Earth's inner core
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DOI：
10.1038/ngeo1808
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发表时间：
2013-07-01
影响因子：
18.3
通讯作者：
Mao, W. L.
中科院分区：
文献类型：
--
作者：
Gleason, A. E.;Mao, W. L.
铁在极端条件下的强度对于解释对地球核心的地球物理观测和理解固体核心如何变形是至关重要的信息(1，2)。然而，铁的强度是变形所依赖的，在高压下测量和准确预测是具有挑战性的。在这里，我们介绍了铁的剪切强度测量，直到地核经历的压力。六方紧密堆积铁的偏向应变的流体静力X射线光谱分析和非流体静力学径向X射线衍射法测量，唯一地确定了其在室温下对200 Gpa以上压力的剪切强度。应用数值模拟铁在压力下的流变行为(3)，将我们的实验结果外推到核心压力和温度，发现在地心、364 Gpa和5,500K的条件下，六方密排铁的整体剪切强度仅相当于1 Gpa，这表明核心的流变很弱，这支持位错蠕变是影响变形的主要蠕变机制。
The strength of iron at extreme conditions is crucial information for interpreting geophysical observations of the Earth's core and understanding how the solid inner core deforms(1,2). However, the strength of iron, on which deformation depends, is challenging to measure and accurately predict at high pressure. Here we present shear strength measurements of iron up to pressures experienced in the Earth's core. Hydrostatic X-ray spectroscopy and non-hydrostatic radial X-ray diffraction measurements of the deviatoric strain in hexagonally close-packed iron uniquely determine its shear strength to pressures above 200 GPa at room temperature. Applying numerical modelling of the rheologic behaviour of iron under pressure(3), we extrapolate our experimental results to inner-core pressures and temperatures, and find that the bulk shear strength of hexagonally close-packed iron is only similar to 1 GPa at the conditions of the Earth's centre, 364 GPa and 5,500 K. This suggests that the inner core is rheologically weak, which supports dislocation creep as the dominant creep mechanism influencing deformation.