Scaling laws for stagnant-lid convection with a buoyant crust
Scaling laws for stagnant-lid convection with a buoyant crust
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DOI：
10.1093/gji/ggab366
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发表时间：
2018-12
影响因子：
2.8
通讯作者：
K. Batra;B. Foley
中科院分区：
文献类型：
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作者：
K. Batra;B. Foley
停滞盖对流，其中俯冲和表面板块运动是不存在的，是常见的岩石行星和卫星在我们的太阳系，并可能在岩石系外行星以及。停滞盖行星如何热演化是一个重要的问题，不仅决定了它们的内部演化，还决定了它们的大气通过火山脱气的演化。在停滞盖行星上，地壳不会因俯冲而再循环，并且可能会变得足够厚，从而显著影响停滞盖下的对流。我们进行数值模型的停滞盖对流，以确定新的对流热通量，特别是占存在一个浮力地壳层的标度律。我们系统地改变地壳层厚度，地壳层密度，瑞利数和Frank-Kamenetskii参数的粘度映射出系统的行为，并确定新的标度律。我们发现两个端员制度的行为：一个“薄地壳极限”，对流在很大程度上不受地壳的存在，和岩石圈的厚度是近似相同的，如果没有地壳;和一个“厚地壳极限”，地壳厚度本身决定了岩石圈的厚度和热通量。两个极限的标度律的开发和拟合的数值模型的结果很好。应用这些标度律岩石滞盖行星，我们发现，对流进入厚地壳极限所需的地壳厚度随着地幔温度的升高和地幔参考粘度的降低而降低。此外，如果地壳厚度受到致密榴辉岩的形成和致密下地壳的沉降的限制，那么较小的行星更有可能进入厚地壳极限，因为它们的地壳可以在达到榴辉岩形成的压力之前变厚。当对流处于厚壳边界时，地幔热通量受到抑制。因此，与地壳较薄的行星相比，地幔温度可以升高100 K，最多可达几Gyr。在行星的热演化过程中，对流是否进入厚地壳极限也取决于初始地幔温度，因此厚的浮力地壳还起到了保护初始条件对停滞盖行星的影响的作用，其时间远远长于以前的热演化模型，该模型忽略了厚地壳的影响。
Stagnant-lid convection, where subduction and surface plate motion is absent, is common among the rocky planets and moons in our solar system, and likely among rocky exoplanets as well. How stagnant-lid planets thermally evolve is an important issue, dictating not just their interior evolution but also the evolution of their atmospheres via volcanic degassing. On stagnant-lid planets, the crust is not recycled by subduction and can potentially grow thick enough to significantly impact convection beneath the stagnant lid. We perform numerical models of stagnant-lid convection to determine new scaling laws for convective heat flux that specifically account for the presence of a buoyant crustal layer. We systematically vary the crustal layer thickness, crustal layer density, Rayleigh number and Frank–Kamenetskii parameter for viscosity to map out system behaviour and determine the new scaling laws. We find two end-member regimes of behaviour: a ‘thin crust limit’, where convection is largely unaffected by the presence of the crust, and the thickness of the lithosphere is approximately the same as it would be if the crust were absent; and a ‘thick crust limit’, where the crustal thickness itself determines the lithospheric thickness and heat flux. Scaling laws for both limits are developed and fit the numerical model results well. Applying these scaling laws to rocky stagnant-lid planets, we find that the crustal thickness needed for convection to enter the thick crust limit decreases with increasing mantle temperature and decreasing mantle reference viscosity. Moreover, if crustal thickness is limited by the formation of dense eclogite, and foundering of this dense lower crust, then smaller planets are more likely to enter the thick crust limit because their crusts can grow thicker before reaching the pressure where eclogite forms. When convection is in the thick crust limit, mantle heat flux is suppressed. As a result, mantle temperatures can be elevated by 100 s of degrees K for up to a few Gyr in comparison to a planet with a thin crust. Whether convection enters the thick crust limit during a planet’s thermal evolution also depends on the initial mantle temperature, so a thick, buoyant crust additionally acts to preserve the influence of initial conditions on stagnant-lid planets for far longer than previous thermal evolution models, which ignore the effects of a thick crust, have found.