Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition
Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition
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DOI：
10.1038/s41561-019-0452-1
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发表时间：
2019-10-01
影响因子：
18.3
通讯作者：
Katsura, Tomoo
中科院分区：
文献类型：
--
作者：
Ishii, Takayuki;Huang, Rong;Katsura, Tomoo
地球地幔的特点是在660公里深处有一个尖锐的地震不连续性，可以提供对深部地幔过程的了解。不连续性发生在只有2公里或0.1 GPa的压力差，并被认为是由于后尖晶石过渡，即矿物ringwoodite分解为bridgmanite加铁方镁石。现有的高压，高温实验缺乏压力控制所需的测试是否这样的尖锐性是由于化学相关系或化学上不同的上，下地幔域。在这里，我们得到的Mg-Fe二元后尖晶石转变的等温压力区间应用先进的多砧技术与原位X射线衍射的帮助下，Mg-Fe分配实验。结果表明，地幔成分和温度的时间间隔仅为0.01GPa，相当于250 m。在地震频率下，该间隔与零不可区分。这些结果可以解释不连续性的尖锐性，并为化学均匀地幔中的全地幔对流提供新的支持。本文的工作表明，绝热垂直流在上地幔和下地幔之间的分布可以根据不连续性的锐度来制图。
The Earth's mantle is characterized by a sharp seismic discontinuity at a depth of 660 km that can provide insights into deep mantle processes. The discontinuity occurs over only 2 km-or a pressure difference of 0.1 GPa-and is thought to result from the post-spinel transition, that is, the decomposition of the mineral ringwoodite to bridgmanite plus ferropericlase. Existing high-pressure, high-temperature experiments have lacked the pressure control required to test whether such sharpness is the result of isochemical phase relations or chemically distinct upper and lower mantle domains. Here, we obtain the isothermal pressure interval of the Mg-Fe binary post-spinel transition by applying advanced multi-anvil techniques with in situ X-ray diffraction with the help of Mg-Fe partition experiments. It is demonstrated that the interval at mantle compositions and temperatures is only 0.01 GPa, corresponding to 250 m. This interval is indistinguishable from zero at seismic frequencies. These results can explain the discontinuity sharpness and provide new support for whole-mantle convection in a chemically homogeneous mantle. The present work suggests that distribution of adiabatic vertical flows between the upper and lower mantles can be mapped on the basis of discontinuity sharpness.