Heat partitioning in terrestrial planets during core formation by negative diapirism
Heat partitioning in terrestrial planets during core formation by negative diapirism
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类地行星在核心形成过程中通过负底辟作用进行热分配
DOI：
10.1016/j.epsl.2009.11.050
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发表时间：
2010
影响因子：
5.3
通讯作者：
M. Evonuk
中科院分区：
文献类型：
--
作者：
H. Samuel;P. J. Tackley;M. Evonuk
我们研究了类地行星中负底辟作用在核心形成过程中硅酸盐和金属相之间的引力热分配。我们模拟了铁底辟穿过固体硅酸盐原地幔下沉的动态演化。我们的计算包括粘性加热以及粘度的强温度和成分依赖性。我们表明，底辟平均温度向渐近值 Td∞ 演化，这取决于底辟与其周围环境之间的粘性加热和传热效率以及粘性流变学。我们推导出了一个简单的分析模型，该模型捕获了数值实验中观察到的热演化。该模型可用于确定具有大量底辟的类地行星在其生长和早期分化过程中的热量分布。我们表明，负底辟作用期间核心地层加热的分配很大程度上取决于铁底辟的尺寸分布。大量的小型下沉铁底辟有利于金属与硅酸盐的热交换，并形成相对较热的核心，这使得可持续的发电机成为可能，就像在地球上一样。少数大型底辟具有相反的效果，可能相当于一颗类似火星的行星，其早期发电机不再活跃。在所有情况下，负底辟作用往往会使最下层地幔的温度明显高于其上部，这可能会引发早期深部地幔的大量融化。
We investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets. We model the dynamic evolution of an iron diapir, sinking through a solid silicate proto-mantle. Our calculations include viscous heating and strong temperature and composition-dependence of viscosity. We show that the diapir mean temperature evolves towards an asymptotic value Td∞, which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings, and on the viscous rheology. We derived a simple analytic model that captures the thermal evolution observed in our numerical experiments. This model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs, during their growth and early differentiation. We show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs. A large number of small sinking iron diapirs favors metal–silicate heat exchange and leads to a relatively hot core, which allows a sustainable dynamo, as on Earth. A small number of large diapirs have the opposite effect and could correspond to a Mars-like planet with an early dynamo that is no longer active. In all cases, negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part, which could trigger large amounts of melting in the early deep mantle.
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