How partial melting affects small-scale convection in a plume-fed sublithospheric layer beneath fast-moving plates
How partial melting affects small-scale convection in a plume-fed sublithospheric layer beneath fast-moving plates
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部分熔融如何影响快速移动板块下方羽流供给的岩石圈下层中的小规模对流
DOI：
10.1002/2015gc005967
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Agrusta R
中科院分区：
文献类型：
--
作者：
Agrusta R
数值模型表明，发生在地幔柱顶部的小尺度对流（SSC）是岩石圈再生的合理机制。SSC的触发取决于密度对比和热边界层（TBL）的停滞上部的不稳定层的流变性。部分熔化可能会改变这两种性质。我们分析，使用2-D数值模拟，部分熔融如何影响随时间变化的SSC不稳定性的动力学和由此产生的热机械复兴的海洋板块移动的顶部的羽。我们的模拟显示了一个复杂的行为，加速，没有变化，或延迟的SSC发病，由于竞争的影响，潜热的部分熔化，冷却羽流材料，和浮力增加与熔体保留和耗尽的残留物后熔体提取。熔体诱导的粘度降低过于局部化而不能显著影响SSC动力学。更快的SSC触发促进低熔化度（低羽流温度异常，厚岩石圈，或快速移动的板块），这限制了温度降低，由于熔化潜热和耗尽的浮力残留物的积累在不稳定层的上部。与此相反，高的部分熔融度导致强烈的温度下降，由于熔化潜热和发展的厚亏损层内的岩石圈对流层，延迟重力不稳定性的发展。尽管在SSC动力学的差异，变薄的岩石圈没有显着增强相对于模拟忽略部分熔融。
Numerical models show that small‐scale convection (SSC) occurring atop a mantle plume is a plausible mechanism to rejuvenate the lithosphere. The triggering of SSC depends on the density contrast and on the rheology of the unstable layer underlying the stagnant upper part of the thermal boundary layer (TBL). Partial melting may change both properties. We analyze, using 2‐D numerical simulations, how partial melting influences the dynamics of time‐dependent SSC instabilities and the resulting thermo‐mechanical rejuvenation of an oceanic plate moving atop of a plume. Our simulations show a complex behavior, with acceleration, no change, or delay of the SSC onset, due to competing effects of the latent heat of partial melting, which cools the plume material, and of the buoyancy increase associated with both melt retention and depletion of residue following melt extraction. The melt‐induced viscosity reduction is too localized to affect significantly SSC dynamics. Faster SSC triggering is promoted for low melting degrees (low plume temperature anomalies, thick lithosphere, or fast moving plates), which limit both the temperature reduction due to latent heat of melting and the accumulation of depleted buoyant residue in the upper part of the unstable layer. In contrast, high partial melting degrees lead to a strong temperate decrease due to latent heat of melting and development of a thick depleted layer within the sublithospheric convecting layer, which delay the development of gravitational instabilities. Despite differences in SSC dynamics, the thinning of the lithosphere is not significantly enhanced relatively to simulations that neglect partial melting.