Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: Implications for Mars
Magma ocean fractional crystallization and cumulate overturn in terrestrial planets: Implications for Mars
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DOI：
10.1111/j.1945-5100.2003.tb00013.x
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发表时间：
2003-12-01
影响因子：
2.2
通讯作者：
Hess, PC
中科院分区：
文献类型：
--
作者：
Elkins-Tanton, LT;Parmentier, EM;Hess, PC
在一个大型类地行星上，岩浆海洋的结晶被吸积能量显著融化，可能导致不稳定的堆积密度分层，这可能会推翻到一个稳定的配置。最初不稳定的地层翻转可能产生早期玄武岩地壳和分异的地幔储层。这种稳定的成分分层可以通过延迟或抑制热对流以及通过影响放射性源的分布对行星的后续演化产生重要影响。我们使用了火星岩浆海洋的简单结晶模型，并计算了由此产生的堆积的密度。虽然所提出的简单模型不包括所有相关的物理过程，但它们能够在一级上描述火星进化的许多方面。这些模型描述了在火星历史早期分化的岩浆源区域的形成，并提出了早期短暂磁场的可能性，该磁场是由落在核心-地幔边界的冷翻转堆积物引发的。在一个包含7.5 GPa密度反演的模型中，橄榄石和辉石漂浮在剩余的岩浆海洋液体中，而石榴石下沉，堆积在火星深处的氧化铝被隔离。源区的年龄和成分与SNC陨石资料一致。
Crystallization of a magma ocean on a large terrestrial planet that is significantly melted by the energy of accretion may lead to an unstable cumulate density stratification, which may overturn to a stable configuration. Overturn of the initially unstable stratification may produce an early basaltic crust and differentiated mantle reservoirs. Such a stable compositional stratification can have important implications for the planet's subsequent evolution by delaying or suppressing thermal convection and by influencing the distribution of radiogenic heat sources. We use simple models for fractional crystallization of a martian magma ocean, and calculate the densities of the resulting cumulates. While the simple models presented do not include all relevant physical processes, they are able to describe to first order a number of aspects of martian evolution. The models describe the creation of magma source regions that differentiated early in the history of Mars, and present the possibility of an early, brief magnetic field initiated by cold overturned cumulates falling to the core-mantle boundary. In a model that includes the density inversion at about 7.5 GPa, where olivine and pyroxene float in the remaining magma ocean liquids while garnet sinks, cumulate overturn sequesters alumina in the deep martian interior. The ages and compositions of source regions are consistent with SNC meteorite data.