Influences on the positioning of mantle plumes following supercontinent formation
Influences on the positioning of mantle plumes following supercontinent formation
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DOI：
10.1002/2014jb011727
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发表时间：
2015-05
期刊：
影响因子：
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通讯作者：
P. Heron;J. Lowman;C. Stein
中科院分区：
文献类型：
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作者：
P. Heron;J. Lowman;C. Stein
一些地幔对流研究分析了超大陆形成和扩散的影响，表明次大陆地幔柱的成因是超大陆边缘俯冲带的形成，而不是大陆热绝缘或热化学堆的影响。然而，俯冲带的位置对陆下地幔柱位置的影响却很少受到关注。本研究分析了超大陆形成（在等化学地幔中）的二维和三维数值模型，以评估俯冲和地幔粘度对比在次大陆地幔柱生成中的作用。我们发现，一旦超大陆的宽度达到临界值，地幔柱就不会在超大陆的中心下形成。在以低粘度下地幔为特征的研究中，初始羽流的表面位置（到达超大陆组装的9000万年内）被锁定在大陆下方距离大陆边缘2000-3000公里的地方。然而，在模拟中，以高粘度下地幔为特征的广泛的下降运动在距离大陆边缘俯冲更远的地方触发了地幔柱。对于所有的地幔粘度剖面，陆下地幔柱表现出对超大陆边缘俯冲位置的依赖性。由于理论对地幔柱形成中核幔边界化学堆的作用存在分歧，因此我们的等化学模型表明，超大陆边缘俯冲带的形成对次大陆地幔动力学有着深远的影响。我们的结果可能有助于解释是什么决定了过去（和未来）大火成岩省的喷发地点。
Several mantle convection studies analyzing the effects of supercontinent formation and dispersal show that the genesis of subcontinental plumes results from the formation of subduction zones at the edges of the supercontinent rather than from the effect of continental thermal insulation or thermochemical piles. However, the influence of subduction zone location on the position of subcontinental plumes has received little attention. This study analyzes 2‐D and 3‐D numerical models of supercontinent formation (in an isochemical mantle) to assess the role of subduction and mantle viscosity contrast in the generation of subcontinental mantle plumes. We find that once a critical supercontinent width is reached, plumes do not form under the center of a supercontinent. In studies featuring a low viscosity lower mantle, the surface positions of the initial plumes (arriving within 90 Myr of supercontinent assembly) become locked beneath the continent at a distance 2000–3000 km from the continental margin. However, the broad downwellings in simulations that feature a high‐viscosity lower mantle trigger plumes at a greater distance from the continental margin subduction. For all mantle viscosity profiles, subcontinental plumes show dependence on the location of supercontinent margin subduction. As theories differ on the role of core‐mantle boundary chemical piles in plume formation, it is significant that our isochemical models show that the formation of subduction zones at the margins of a supercontinent has a profound effect on subcontinental mantle dynamics. Our results may help to explain what determined the eruption sites of past (and future) large igneous provinces.