Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity
Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity
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超级地球中的地幔动力学：后钙钛矿流变学和粘度的自我调节
DOI：
10.1016/j.icarus.2013.03.013
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发表时间：
2013
期刊：
影响因子：
3.2
通讯作者：
Tackley P
中科院分区：
文献类型：
--
作者：
Tackley P
尺寸达到地球两倍的太阳系外“超级地球”行星的发现引发了人们对其可能的岩石圈和地幔动力学和演化的兴趣。简单的缩放表明，超级地球比同等大小的地球行星更有可能经历板块构造。一般来说，粘度和导热系数随着压力的增加而增加，而热膨胀性则降低，导致深部地幔中的对流活力较低，如果将其延伸到最大的超级地球，根据传统的想法，由于有效瑞利数非常低，可能会导致其深部地幔中没有对流。在此我们对此进行评价。首先，由于超级地球的地幔主要由后钙钛矿构成，我们在这里将后钙钛矿活化焓的密度泛函理论 (DFT) 计算扩展到 1TPa 的压力，对于最慢扩散（上限流变学）和最快扩散（下限流变学）方向。沿着 1600K 绝热，上限流变性将导致后钙钛矿层具有非常高（~1030Pas）但相对均匀的粘度，而下限流变性导致后钙钛矿层粘度随深度增加~7 个数量级；在这两种情况下，深部地幔粘度对于对流来说都太高了。其次，我们使用这些 DFT 计算值对具有十个地球质量的行星的地幔对流和岩石圈动力学进行统计稳态数值模拟。该模型假设了一个可压缩的地幔，包括材料特性的深度依赖性和塑性屈服引起的板状岩石圈行为。结果证实了具有与地球类似的表面条件（温度和水）的行星的板块构造的可能性，并显示了深层地幔温度的自我调节。深部地幔不是绝热的；相反，内部加热、温度和粘度之间的反馈调节温度，使得粘度具有促进放射热对流损失所需的值，从而产生用于上限流变学的非常热的钙钛矿层，用于下限流变学的超绝热钙钛矿层，以及不超过1026Pas的方位平均粘度。大型超级地球中的对流的特点是大的上升流（即使基础加热为零）和小的、随时间变化的下降流，对于大型超级地球来说，下降流合并成广泛的下降流。在行星演化的背景下，如果超级地球在形成后非常热/熔化（很可能是这样），那么即使在数十亿年之后，它的深层内部仍然非常热，并且可能基本上熔化为“超级基底岩浆海洋”——拉布罗斯等人的提议的放大版本。 （Labrosse, S., Hernlund, J.W., Coltice, N. [2007]. Nature 450, 866–869），尽管这取决于目前未知的熔体-固体密度对比和固相线。
The discovery of extra-solar “super-Earth” planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigour in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result in no convection in their deep mantles due to the very low effective Rayleigh number. Here we evaluate this. First, as the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1TPa, for both slowest diffusion (upper-bound rheology) and fastest diffusion (lower-bound rheology) directions. Along a 1600K adiabat the upper-bound rheology would lead to a post-perovskite layer of a very high (∼1030Pas) but relatively uniform viscosity, whereas the lower-bound rheology leads to a post-perovskite viscosity increase of ∼7 orders of magnitude with depth; in both cases the deep mantle viscosity would be too high for convection. Second, we use these DFT-calculated values in statistically steady-state numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behaviour. Results confirm the likelihood of plate tectonics for planets with Earth-like surface conditions (temperature and water) and show a self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead feedback between internal heating, temperature and viscosity regulates the temperature such that the viscosity has the value needed to facilitate convective loss of the radiogenic heat, which results in a very hot perovskite layer for the upper-bound rheology, a super-adiabatic perovskite layer for the lower-bound rheology, and an azimuthally-averaged viscosity of no more than 1026Pas. Convection in large super-Earths is characterised by large upwellings (even with zero basal heating) and small, time-dependent downwellings, which for large super-Earths merge into broad downwellings. In the context of planetary evolution, if, as is likely, a super-Earth was extremely hot/molten after its formation, it is thus likely that even after billions of years its deep interior is still extremely hot and possibly substantially molten with a “super basal magma ocean” – a larger version of the proposal of Labrosse et al. (Labrosse, S., Hernlund, J.W., Coltice, N. [2007]. Nature 450, 866–869), although this depends on presently unknown melt–solid density contrast and solidus.
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影响因子：
5.3
作者：
C. O'Neill;A. Lenardic;Louis Moresi;T. Torsvik;Cin-Ty A. Lee
通讯作者：
C. O'Neill;A. Lenardic;Louis Moresi;T. Torsvik;Cin-Ty A. Lee
DOI：
10.1088/2041-8205/726/2/l15
发表时间：
2010-09
期刊：
The Astrophysical Journal Letters
影响因子：
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作者：
S. Wanajo;H. Janka;B. Mueller
通讯作者：
S. Wanajo;H. Janka;B. Mueller
从第一原理看铝在氧化镁中的扩散
影响因子：
1.4
作者：
M. Ammann;J. Brodholt;D. Dobson
通讯作者：
D. Dobson
影响因子：
3.7
作者：
J. Hewitt;D. McKenzie;N. Weiss
通讯作者：
N. Weiss
包括地核冷却在内的地幔对流动态模型和参数化模型的比较
影响因子：
5.3
作者：
S. Honda;Y. Iwase
通讯作者：
Y. Iwase