Post-Perovskite Phase Transition in the Pyrolitic Lowermost Mantle: Implications for Ubiquitous Occurrence of Post-Perovskite Above CMB
Post-Perovskite Phase Transition in the Pyrolitic Lowermost Mantle: Implications for Ubiquitous Occurrence of Post-Perovskite Above CMB
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DOI：
10.1029/2021gl096219
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发表时间：
2022-01-16
影响因子：
5.2
通讯作者：
Ohishi, Yasuo
中科院分区：
文献类型：
--
作者：
Kuwayama, Yasuhiro;Hirose, Kei;Ohishi, Yasuo
我们进行了原位高压和高温X射线衍射测量的热解地幔材料高达4480 K，在122-166 GPa的激光加热金刚石对顶砧。结果表明，即使在>4000 K，地幔压力最低的范围内，地幔岩中也发生了钙钛矿和后钙钛矿之间的相变。这表明在核幔边界上方普遍存在后钙钛矿，这可能与最近的高质量地震数据相一致，即未观察到D”反射是例外。结合早期在正常下地幔地温及以下进行的实验，我们的数据表明，桥镁石+后钙钛矿两相区的厚度类似于5 GPa，边界的dP/dT斜率为+6.5 +/- 2.2 MPa/K，略小于以前在MgSiO 3中的理论计算。地幔底部流变性弱的后钙钛矿在全球范围内的存在对地震学、地球动力学和地核热传递有着深远的影响。
We conducted in situ high-pressure and -temperature X-ray diffraction measurements of a pyrolitic mantle material up to 4480 K at 122-166 GPa in a laser-heated diamond anvil cell. Results demonstrate that the phase transition between bridgmanite and post-perovskite occurs in pyrolite within the lowermost mantle pressure range even at >4000 K. It suggests the ubiquitous occurrence of post-perovskite above the core-mantle boundary, which may be consistent with recent high-quality seismology data that non-observations of D" reflections are exceptions. Combining with earlier experiments performed at and below the normal lower-mantle geotherm, our data show that the bridgmanite + post-perovskite two-phase region is similar to 5 GPa thick and the dP/dT slope of the boundary is +6.5 +/- 2.2 MPa/K, slightly smaller than previous theoretical calculations in MgSiO3. The global presence of rheologically weak post-perovskite at the bottom of the mantle has profound implications in seismology, geodynamics, and heat transfer from the core.