Changes in core-mantle boundary heat flux patterns throughout the supercontinent cycle
Changes in core-mantle boundary heat flux patterns throughout the supercontinent cycle
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DOI：
10.1093/gji/ggae075
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发表时间：
2024-04-09
影响因子：
2.8
通讯作者：
Sprain，Courtney
中科院分区：
文献类型：
--
作者：
Dannberg，Juliane;Gassmoller，Rene;Sprain，Courtney
地球的磁场是由外核的发电机产生的，对保护我们的星球免受有害辐射至关重要。尽管核心-地幔边界热通量作为发电机驱动因素的重要性已经确立，但关于热通量非均质性如何影响磁场的问题仍然存在。本文利用地球动力学建模软件ASPECT中的可压缩全球三维地幔对流模型，探讨了地球核幔边界热通量的分布及其随时间的变化。讨论了在有限元模拟中使用一致边界通量法作为更精确地计算边界热通量的工具，以及在地球动力学模拟中将计算得到的热通量图作为边界条件的工作流程。我们的模型使用过去10亿年的板块重建——包括完整的超大陆旋回——来确定俯冲板块的位置和下沉速度。结果表明，地幔上升流和下升流如何在核心-地幔边界产生局部热通量异常，这种异常在地球历史上可能会发生巨大变化，并取决于最下层地幔的性质和演化以及表面俯冲带的配置。在整个超大陆旋回中，核心-地幔边界的冷热结构的分布在位置、形状和数量上都发生了变化，这表明这些结构在地球过去可能是波动的，看起来可能非常不同。我们的研究结果对理解地球的热演化及其磁场在地质时间尺度上的稳定性具有重要意义。它们提供了对地幔对磁场的潜在影响的见解，并为进一步探索有关内核成核和最下层地幔过去状态的问题铺平了道路。
The Earth's magnetic field is generated by a dynamo in the outer core and is crucial for shielding our planet from harmful radiation. Despite the established importance of the core-mantle boundary heat flux as driver for the dynamo, open questions remain about how heat flux heterogeneities affect the magnetic field. Here, we explore the distribution of core-mantle boundary heat flux on Earth and its changes over time using compressible global 3-D mantle convection models in the geodynamic modeling software ASPECT. We discuss the use of the consistent boundary flux method as a tool to more accurately compute boundary heat fluxes in finite element simulations and the workflow to provide the computed heat flux patterns as boundary conditions in geodynamo simulations. Our models use a plate reconstruction throughout the last 1 billion years -- encompassing the complete supercontinent cycle -- to determine the location and sinking speed of subducted plates. The results show how mantle upwellings and downwellings create localized heat flux anomalies at the core-mantle boundary that can vary drastically over Earth's history and depend on the properties and evolution of the lowermost mantle as well as the surface subduction zone configuration. The distribution of hot and cold structures at the core-mantle boundary changes throughout the supercontinent cycle in terms of location, shape and number, indicating that these structures fluctuate and might have looked very differently in Earth's past. Our results have implications for understanding the Earth's thermal evolution and the stability of its magnetic field over geological timescales. They provide insights into the potential effects of the mantle on the magnetic field and pave the way for further exploring questions about the nucleation of the inner core and the past state of the lowermost mantle.