Water distribution in the lower mantle: Implications for hydrolytic weakening
Water distribution in the lower mantle: Implications for hydrolytic weakening
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DOI：
10.1016/j.epsl.2017.11.051
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发表时间：
2018-02
影响因子：
5.3
通讯作者：
J. Muir;J. Brodholt
中科院分区：
文献类型：
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作者：
J. Muir;J. Brodholt
下地幔矿物中水的存在被认为对地球下地幔的流变特性有实质性的影响，这通常被称为“水解弱化”。这种减弱将对全球对流产生深远的影响，但下地幔矿物的水解减弱尚未在实验中观察到，因此水对全球动力学的影响仍然是推测性的。为了约束水解弱化在下地幔中是重要的可能性，我们使用第一性原理方法来计算下地幔条件下下地幔矿物相之间的水（严格的质子）分配。我们发现，在整个下地幔中，水主要存在于少量钙钛矿相或以Al3+ -H +对的形式存在于桥锰矿中。铁长石保持干燥。然而，这两种吸水方法都不会在桥菱石中产生额外的空位，因此水解弱化的影响可能很小。我们发现，水只在下地幔的最深处，并且只有在非常高的含水量（> 1000ppm）时，才会在桥辉石中产生大量的空位。因此，我们得出结论，水可能对下地幔的流变特性只有有限的影响。
The presence of water in lower mantle minerals is thought to have substantial effects on the rheological properties of the Earth's lower mantle in what is generally known as “hydrolytic weakening”. This weakening will have profound effects on global convection, but hydrolytic weakening in lower mantle minerals has not been observed experimentally and thus the effect of water on global dynamics remains speculative. In order to constrain the likelihood of hydrolytic weakening being important in the lower mantle, we use first principles methods to calculate the partitioning of water (strictly protons) between mineral phases of the lower mantle under lower mantle conditions. We show that throughout the lower mantle water is primarily found either in the minor Ca-perovskite phase or in bridgmanite as an Al3+–H+pair. Ferropericlase remains dry. However, neither of these methods of water absorption creates additional vacancies in bridgmanite and thus the effect of hydrolytic weakening is likely to be small. We find that water creates significant number of vacancies in bridgmanite only at the deepest part of the lower mantle and only for very high water contents (>1000 ppm). We conclude that water is thus likely to have only a limited effect on the rheological properties of the lower mantle.