Tsujino Noriyoshi, Yamazaki Daisuke, Nishihara Yu, Yoshino Takashi, Higo Yuji, Tange Yoshinori
Institute for Planetary Materials, Okayama University, 27 Yamada, Misasa, Tottori 682-0193, Japan.
Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
Sci Adv. 2022 Apr;8(13):eabm1821. doi: 10.1126/sciadv.abm1821. Epub 2022 Mar 30.
To understand mantle dynamics, it is important to determine the rheological properties of bridgmanite, the dominant mineral in Earth's mantle. Nevertheless, experimental data on the viscosity of bridgmanite are quite limited due to experimental difficulties. Here, we report viscosity and deformation mechanism maps of bridgmanite at the uppermost lower mantle conditions obtained through in situ stress-strain measurements of bridgmanite using deformation apparatuses with the Kawai-type cell. Bridgmanite would be the hardest among mantle constituent minerals even under nominally dry conditions in the dislocation creep region, consistent with the observation that the lower mantle is the hardest layer. Deformation mechanism maps of bridgmanite indicate that grain size of bridgmanite and stress conditions at top of the lower mantle would be several millimeters and ~10 Pa to realize viscosity of 10 Pa·s, respectively. This grain size of bridgmanite suggests that the main part of the lower mantle is isolated from the convecting mantle as primordial reservoirs.
为了理解地幔动力学，确定布里奇曼石（地球地幔中的主要矿物）的流变性质非常重要。然而，由于实验困难，关于布里奇曼石粘度的实验数据相当有限。在此，我们报告了通过使用带有川井型高压腔的变形装置对布里奇曼石进行原位应力 - 应变测量所获得的、在下地幔最上部条件下布里奇曼石的粘度和变形机制图。即使在名义上干燥的条件下，在位错蠕变区域中，布里奇曼石在地幔组成矿物中也是最硬的，这与下地幔是最硬层的观测结果一致。布里奇曼石的变形机制图表明，在下地幔顶部，布里奇曼石的晶粒尺寸和应力条件分别约为几毫米和约10帕斯卡，以实现10帕斯卡·秒的粘度。布里奇曼石的这种晶粒尺寸表明下地幔的主要部分作为原始储库与对流地幔隔离。
