Based on the standard view of depth-increasing viscosity in the mantle of rocky planets, convection in the deep mantle of these planets is expected to become less likely as the size of planet increases. However, a recent theoretical study suggests that above 100 GPa pressure, the mantle viscosity can instead decrease with pressure at higher depths. We explore the potential impact of this type of viscosity structure on the nature of mantle convection in a super-Earth planet of size GJ 876 d with a mass of ∼7.33 M_⊕ (M_⊕: Earth's mass). The pressures at the bottom of the mantle of GJ 876 d allow MgSiO₃ post-perovskite to dissociate into magnesium oxide (MgO) and relatively highly oxidized magnesium silicate MgSi₂O₅ at 0.9 TPa with highly negative Clapeyron slope. Our 3D-spherical numerical model results suggest that for sufficiently low values of viscosity at the transition depth, a vigorous layered mantle convection may develop at the bottom of GJ 876 d-size super-Earth. Focused penetrative plumes originating from the deep mantle layered region can survive and stabilize over very long geological timescales and reach to the surface, which may induce unique circumstances of volcanism and tectonic activity.

中文翻译：

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聚焦穿透羽流：大质量岩石超级地球中约 0.9 TPa 后钙钛矿离解转变的可能后果

根据岩石行星地幔中深度增加粘度的标准观点，随着行星尺寸的增加，这些行星地幔深处的对流预计将变得不太可能。然而，最近的一项理论研究表明，当压力高于 100 GPa 时，地幔粘度反而会随着更深深度的压力而降低。我们探索了这种类型的粘度结构对一颗质量为~7.33 M _⊕（M _⊕：地球质量）的超级地球行星的地幔对流性质的潜在影响，该行星的大小为 GJ 876 d 。GJ 876 d 地幔底部的压力使钙钛矿后的MgSiO ₃分解为氧化镁 (MgO) 和相对高度氧化的硅酸镁 MgSi ₂ O ₅在 0.9 TPa 下，克拉珀龙斜率非常负。我们的 3D 球形数值模型结果表明，对于过渡深度处足够低的粘度值，可能会在 GJ 876 d 级超级地球底部形成剧烈的层状地幔对流。源自深部地幔层状区域的集中穿透羽流可以在很长的地质时间尺度内存活和稳定并到达地表，这可能会引发独特的火山活动和构造活动环境。