Water circulation and global mantle dynamics: Insight from numerical modeling

Water circulation and global mantle dynamics: Insight from numerical modeling
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DOI：
10.1002/2014gc005701
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发表时间：
2015-05
期刊：
Geochemistry
影响因子：
3.7
通讯作者：
T. Nakagawa;T. Nakakuki;H. Iwamori
T. Nakagawa;T. Nakakuki;H. Iwamori
中科院分区：
地球科学3区
文献类型：
--
作者：
T. Nakagawa;T. Nakakuki;H. Iwamori

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在热化学地幔对流数值模拟中，我们研究了水循环及其对全球尺度地幔动力学的影响。包括脱水-水化过程和脱水熔融过程。我们还假设了含水矿物的流变性和由含水矿物引起的密度降低。在地幔对流系统中，地幔对流的换热似乎比水循环更有效，当假定粘度与水的关系合理时，这是因为在浅层有有效的板块脱水。与干燥地幔相比，水削弱了近地表洋壳和岩石圈，增强了地表板块运动的活跃性，从而仍然对全球动力学产生了重大影响。因此，包括含水矿物在内，粘性更强的地幔预计会比干燥的地幔高出几个数量级。整个地幔的平均含水率受脱水-水化过程的调节。当假设玄武岩物质与周围地幔之间的密度差很大(4-5%)时，就会发现大规模的热化学异常，就像在深部地幔观察到的那样，与矿物物理测量结果相当。通过这项研究，水合矿物在地幔动力学中的作用对于解释地幔对流的观测约束是非常重要的。
We investigate water circulation and its dynamical effects on global‐scale mantle dynamics in numerical thermochemical mantle convection simulations. Both dehydration‐hydration processes and dehydration melting are included. We also assume the rheological properties of hydrous minerals and density reduction caused by hydrous minerals. Heat transfer due to mantle convection seems to be enhanced more effectively than water cycling in the mantle convection system when reasonable water dependence of viscosity is assumed, due to effective slab dehydration at shallow depths. Water still affects significantly the global dynamics by weakening the near‐surface oceanic crust and lithosphere, enhancing the activity of surface plate motion compared to dry mantle case. As a result, including hydrous minerals, the more viscous mantle is expected with several orders of magnitude compared to the dry mantle. The average water content in the whole mantle is regulated by the dehydration‐hydration process. The large‐scale thermochemical anomalies, as is observed in the deep mantle, is found when a large density contrast between basaltic material and ambient mantle is assumed (4–5%), comparable to mineral physics measurements. Through this study, the effects of hydrous minerals in mantle dynamics are very important for interpreting the observational constraints on mantle convection.