Deep and persistent melt layer in the Archaean mantle
Deep and persistent melt layer in the Archaean mantle
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DOI：
10.1038/s41561-017-0053-9
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发表时间：
2018-02-01
影响因子：
18.3
通讯作者：
Hennet, Louis
中科院分区：
文献类型：
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作者：
Andrault, Denis;Pesce, Giacomo;Hennet, Louis
从侏罗纪到元古宙的过渡结束了地球表面一段极不稳定的时期。这一转变的起源可能是地球内部动态机制的变化。在这里，我们使用实验室实验来调查的固相线的样品代表的上地幔。我们的两个互补的熔融曲线的原位测量揭示了一个固相线，这是200-250 K低于以前报道的深度高于约100公里。如此低的固相线温度使得今天的部分熔化比以前认为的更容易，特别是在挥发物（H2O和CO2）存在的情况下。较低的固相线也可以解释早期高产量的熔体，如科马提岩。对于一个比今天热200-300 K的地幔，预计在100-150公里到400公里以上的深度会发生显著的熔融。因此，在侏罗纪上地幔中可能存在一个持续的熔融层。由于地幔的长期冷却，这种熔融物质的外壳可能已经逐渐消失。结晶会增加上地幔的粘度，并可能增强岩石圈和软流圈之间的机械耦合。这种变化可能解释了从早期地球上由停滞盖主导的表面动力学到具有深板俯冲的现代板块构造的转变。
The transition from the Archaean to the Proterozoic eon ended a period of great instability at the Earth's surface. The origin of this transition could be a change in the dynamic regime of the Earth's interior. Here we use laboratory experiments to investigate the solidus of samples representative of the Archaean upper mantle. Our two complementary in situ measurements of the melting curve reveal a solidus that is 200-250 K lower than previously reported at depths higher than about 100 km. Such a lower solidus temperature makes partial melting today easier than previously thought, particularly in the presence of volatiles (H2O and CO2). A lower solidus could also account for the early high production of melts such as komatiites. For an Archaean mantle that was 200-300 K hotter than today, significant melting is expected at depths from 100-150 km to more than 400 km. Thus, a persistent layer of melt may have existed in the Archaean upper mantle. This shell of molten material may have progressively disappeared because of secular cooling of the mantle. Crystallization would have increased the upper mantle viscosity and could have enhanced mechanical coupling between the lithosphere and the asthenosphere. Such a change might explain the transition from surface dynamics dominated by a stagnant lid on the early Earth to modern-like plate tectonics with deep slab subduction.