The ancient cores of continents (cratons) are underlain by mantle keels-volumes of melt-depleted, mechanically resistant, buoyant and diamondiferous mantle up to 350 kilometres thick, which have remained isolated from the hotter and denser convecting mantle for more than two billion years. Mantle keels formed only in the Early Earth (approximately 1.5 to 3.5 billion years ago in the Precambrian eon); they have no modern analogues1-4. Many keels show layering in terms of degree of melt depletion5-7. The origin of such layered lithosphere remains unknown and may be indicative of a global tectonics mode (plate rather than plume tectonics) operating in the Early Earth. Here we investigate the possible origin of mantle keels using models of oceanic subduction followed by arc-continent collision at increased mantle temperatures (150-250 degrees Celsius higher than the present-day values). We demonstrate that after Archaean plate tectonics began, the hot, ductile, positively buoyant, melt-depleted sublithospheric mantle layer located under subducting oceanic plates was unable to subduct together with the slab. The moving slab left behind craton-scale emplacements of viscous protokeel beneath adjacent continental domains. Estimates of the thickness of this sublithospheric depleted mantle show that this mechanism was efficient at the time of the major statistical maxima of cratonic lithosphere ages. Subsequent conductive cooling of these protokeels would produce mantle keels with their low modern temperatures, which are suitable for diamond formation. Precambrian subduction of oceanic plates with highly depleted mantle is thus a prerequisite for the formation of thick layered lithosphere under the continents, which permitted their longevity and survival in subsequent plate tectonic processes.

中文翻译：

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在前寒武纪板块构造中建造克拉通龙骨

大陆的古老核心（克拉通）下面是地幔龙骨——大量熔体耗尽、机械抗性、浮力和含金刚石的地幔，厚度达 350 公里，在超过 20 亿年的时间里，这些地幔与更热、更密集的对流地幔保持隔离. 地幔龙骨仅在地球早期形成（大约 1.5 到 35 亿年前的前寒武纪）；他们没有现代类似物1-4。许多龙骨在熔体消耗程度方面表现出分层5-7。这种层状岩石圈的起源仍然未知，可能表明早期地球存在全球构造模式（板块而非羽状构造）。在这里，我们使用海洋俯冲模型研究地幔龙骨的可能起源，然后在地幔温度升高（比现在的值高 150-250 摄氏度）下进行弧形大陆碰撞。我们证明，在太古代板块构造开始后，位于俯冲大洋板块下方的高温、韧性、正浮力、熔体贫化的亚岩石圈地幔层无法与板片一起俯冲。移动的板块在相邻大陆域下方留下了克拉通级粘性原龙骨的位置。对这个亚岩石圈贫化地幔厚度的估计表明，这种机制在克拉通岩石圈年龄的主要统计最大值时期是有效的。这些原龙骨的后续传导冷却将产生现代低温的地幔龙骨，适合钻石形成。因此，前寒武纪前寒武纪大洋板块的俯冲具有高度贫化的地幔，是大陆下形成厚层状岩石圈的先决条件，这使得它们在随后的板块构造过程中得以长寿和生存。