In situ measurements of the phase transition boundary in Mg3Al2Si3O12: implications for the nature of the seismic discontinuities in the Earth’s mantle
In situ measurements of the phase transition boundary in Mg3Al2Si3O12: implications for the nature of the seismic discontinuities in the Earth’s mantle
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DOI：
10.1016/s0012-821x(00)00354-x
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发表时间：
2001-01
影响因子：
5.3
通讯作者：
K. Hirose;Y. Fei;S. Ono;T. Yagi;K. Funakoshi
中科院分区：
文献类型：
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作者：
K. Hirose;Y. Fei;S. Ono;T. Yagi;K. Funakoshi
在这里，我们报告的镁铝榴石石榴石（Mg3 Al 2Si 3 O 12）的相边界的含铝硅酸盐钙钛矿加SiO2，在高温下的多砧装置原位测量确定的最高转变压力。还通过原位X射线测量评价了不同标准的Au、NaCl、Pt、W和Mo在高温下的压力标度的一致性。我们的结果，连同最近在Mg 2SiO 4中的后尖晶石转变的原位测量[Irifune等人，Science 279（1998）1698-1700]和MgSiO 3中的钛铁矿-钙钛矿转变[Ono等人，地球物理学家。Res. Lett.（2000）提交]，表明在常规淬火实验中确定的压力[Ito和Takahashi，J. Geophys. Res. 94（1989）10637-10646]在对应于过渡区底部的压力下可能被高估了2GPa以上。根据现场测量，后尖晶石过渡发生在一个深度（10600公里），这是太浅，以配合在地球的地幔660公里的地震不连续。因此，一个以橄榄石为主的地幔成分模型可能与地震观测不一致。或者，我们提出了一个辉石-石榴石为主的过渡带与适当的Al 2 O3含量（约。6-8在660 km的不连续面处，镁铝榴石向钙钛矿转变。任何替代模型都必须考虑地幔中的化学分层。
Here we report the phase boundary of pyrope garnet (Mg3Al2Si3O12) to Al-bearing silicate perovskite plus corundum, with the highest transition pressure determined by in situ measurements in a multi-anvil apparatus at high temperature. The consistency of the pressure scales by different standards of Au, NaCl, Pt, W, and Mo at high temperature was also evaluated by in situ X-ray measurements. Our results, together with recent in situ measurements of the post-spinel transition in Mg2SiO4[Irifune et al., Science 279 (1998) 1698–1700] and the ilmenite–perovskite transition in MgSiO3[Ono et al., Geophys. Res. Lett. (2000) submitted], show that pressures determined in conventional quench experiments [Ito and Takahashi, J. Geophys. Res. 94 (1989) 10637–10646] could have been overestimated by more than 2 GPa at pressures corresponding to the bottom of the transition zone. On the basis of the in situ measurements, the post-spinel transition occurs at a depth (∼600 km) that is too shallow to match with the 660-km seismic discontinuity in the Earth’s mantle. Therefore, an olivine dominant mantle compositional model may be inconsistent with the seismic observations. Alternatively, we propose a pyroxene–garnet dominant transition zone with an appropriate Al2O3content (ca. 6–8 mol%), in which majorite garnet transforms to perovskite at the depth of the 660-km discontinuity. Any alternative models would have to consider chemical stratification in the mantle.