Cao Xianzhi, Flament Nicolas, Bodur Ömer F, Müller R Dietmar
Frontiers Science Center for Deep Ocean Multispheres and Earth System; Key Lab of Submarine Geosciences and Prospecting Techniques, MOE, and College of Marine Geosciences, Ocean University of China, Qingdao, 266100, China.
EarthByte Group, School of Geosciences, The University of Sydney, Sydney, NSW, Australia.
Sci Rep. 2021 Nov 25;11(1):22967. doi: 10.1038/s41598-021-02359-z.
Seismic studies have revealed two Large Low-Shear Velocity Provinces (LLSVPs) in the lowermost mantle. Whether these structures remain stable over time or evolve through supercontinent cycles is debated. Here we analyze a recently published mantle flow model constrained by a synthetic plate motion model extending back to one billion years ago, to investigate how the mantle evolves in response to changing plate configurations. Our model predicts that sinking slabs segment the basal thermochemical structure below an assembling supercontinent, and that this structure eventually becomes unified due to slab push from circum-supercontinental subduction. In contrast, the basal thermochemical structure below the superocean is generally coherent due to the persistence of a superocean in our imposed plate reconstruction. The two antipodal basal thermochemical structures exchange material several times when part of one of the structures is carved out and merged with the other one, similarly to "exotic" tectonic terranes. Plumes mostly rise from thick basal thermochemical structures and in some instances migrate from the edges towards the interior of basal thermochemical structures due to slab push. Our results suggest that the topography of basal structures and distribution of plumes change over time due to the changing subduction network over supercontinent cycles.
地震研究揭示了下地幔中存在两个大型低剪切波速度省（LLSVPs）。这些结构是否随时间保持稳定，还是会在超大陆旋回中演化，目前仍存在争议。在此，我们分析了一个最近发表的地幔流动模型，该模型受一个可追溯到十亿年前的合成板块运动模型的约束，以研究地幔如何响应不断变化的板块构造而演化。我们的模型预测，下沉板块会在正在聚合的超大陆下方分割基底热化学结构，并且由于环绕超大陆俯冲作用产生的板块推力，这种结构最终会变得统一。相比之下，由于在我们设定的板块重建中超级海洋的持续存在，超级海洋下方的基底热化学结构通常是连贯的。当其中一个结构的一部分被分割出来并与另一个结构合并时，这两个对映的基底热化学结构会多次交换物质，类似于“外来”构造地体。地幔柱大多从厚实的基底热化学结构中升起，在某些情况下，由于板块推力，地幔柱会从基底热化学结构的边缘向内部迁移。我们的结果表明，由于超大陆旋回中俯冲网络的变化，基底结构的地形和地幔柱的分布会随时间发生变化。
