Thermo-chemical evolution and global contraction of mercury
Thermo-chemical evolution and global contraction of mercury
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DOI：
10.1016/j.epsl.2011.04.040
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发表时间：
2011-07-01
影响因子：
5.3
通讯作者：
Laneuville, M.
中科院分区：
文献类型：
--
作者：
Grott, M.;Breuer, D.;Laneuville, M.
在水星表面观察到的非常有限的全球收缩对行星的热化学演化模型造成了严重的限制，目前的模型依赖于一种非常难熔的、富含钍的成分来减缓行星的冷却。然而，耐火成分似乎与火山碎屑喷发的证据不相容，火山碎屑喷发需要大量的挥发物存在于行星内部。此外，火山活动似乎在地球历史的相当一部分时间里一直在进行，而目前的模型预测地壳生产会提前停止。为了解决这些矛盾，我们重新研究了热化学演化的汞使用非耐火材料的组成模型，考虑到存在的隔热风化层。我们发现，如果风化层至少有2公里厚的刚性地幔流变模型满足观测约束。在这些模型中，低效率的地幔对流和热绝缘显着减缓行星冷却，并延长地壳生产阶段至核心形成后的2.5 Gyr，允许与地幔分化相关的体积增加，以抵消行星冷却引起的一些径向收缩。模型还预测了显著的堆芯硫含量高于6重量%，平均地壳厚度在10和40公里之间，长期冷却速率为30 K/Gyr。(c)2011 Elsevier B. V.保留所有权利。
The very limited amount of global contraction observed on Mercury's surface poses severe constraints on models of the planet's thermo-chemical evolution and current models rely on a very refractory, Thorium rich composition to slow planetary cooling. However, a refractory composition appears to be incompatible with evidence for pyroclastic eruptions, which require a substantial amount of volatiles to be present in the planetary interior. Furthermore, volcanic activity appears to have been ongoing for a considerable part of the planet's history, while current models predict an early cessation of crustal production. To address these inconsistencies we have reinvestigated the thermo-chemical evolution of Mercury using a non-refractory compositional model, taking the presence of a thermally insulating regolith layer into account. We find that models with a stiff mantle rheology satisfy the observational constraints if the regolith layer is at least 2 km thick. In these models, inefficient mantle convection and thermal insulation significantly slow planetary cooling and prolong the phase of crustal production to 2.5 Gyr after core formation, allowing the volume increase associated with mantle differentiation to offset some of the radial contraction caused by planetary cooling. Models furthermore predict substantial core sulfur contents above 6 wt.%, average crustal thicknesses between 10 and 40 km, and secular cooling rates of 30 K/Gyr. (c) 2011 Elsevier B.V. All rights reserved.