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Deep Water Cycling and the Multi‐Stage Cooling of the Earth
Geochemistry, Geophysics, Geosystems ( IF 4.480 ) Pub Date : 2020-09-17 , DOI: 10.1029/2020gc009106
J. Seales 1 , A. Lenardic 1
Affiliation  

Paleo‐temperature data indicates that the Earth's mantle has not cooled at a constant rate. The data show slow cooling from 3.8 to 2.5 Ga followed by more rapid cooling until the present. This has been argued to indicate a transition from a single plate mode to a plate tectonics. However, a tectonic change may not be necessary. Multistage cooling can result from deep water cycling coupled to mantle convection. Melting and volcanism removes water from the mantle (degassing). Dehydration tends to stiffen the mantle, which slows convective vigor and plate velocities causing mantle heating. Higher mantle temperature tends to lower mantle viscosity and increase plate velocities. If these two tendencies are in balance, then mantle cooling can be weak. Breaking this balance, via a switch to net mantle rehydration, can cool the mantle more rapidly. We use coupled water cycling and mantle convection models to test the viability of this hypothesis. Within model and data uncertainty, the hypothesis that deep water cycling can lead to a multi‐stage Earth cooling is consistent with data constraints. Probability distributions, for successful models, indicate that plate and plate margin strength play a minor role for resisting plate motions relative to the resistance from interior mantle viscosity.

中文翻译:

深水循环和地球的多阶段冷却

古温度数据表明地球的地幔并未以恒定的速度冷却。数据显示从3.8 Ga缓慢冷却至2.5 Ga,然后冷却直至目前。有人认为这表明从单板模式向板构造过渡。但是,构造变化可能不是必需的。多级冷却可能是由于深水循环与地幔对流耦合造成的。融化和火山作用将地幔中的水清除(脱气)。脱水趋于使地幔变硬,从而减慢对流活力和板速,从而引起地幔加热。较高的地幔温度往往会降低地幔粘度并增加板速。如果这两种趋势保持平衡,那么地幔冷却可能会很弱。通过转换为地幔补水,打破这种平衡,可以更快地冷却地幔。我们使用耦合水循环和地幔对流模型来检验该假设的可行性。在模型和数据不确定性的范围内,深水循环可能导致多级地球降温的假设与数据约束相一致。对于成功的模型,概率分布表明,板和板的边缘强度相对于抵抗内部地幔粘度的阻力在抵抗板运动方面起着较小的作用。
更新日期:2020-10-06
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