Channeling instability of upwelling melt in the mantle
Channeling instability of upwelling melt in the mantle
复制标题
地幔上升流熔体的通道不稳定性
DOI：
10.1029/95jb01307
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发表时间：
1995
影响因子：
--
通讯作者：
M. Spiegelman
中科院分区：
文献类型：
--
作者：
E. Aharonov;J. Whitehead;P. Kelemen;M. Spiegelman
我们提出了一项理论研究的结果，旨在了解从上地幔中提取的熔体。具体来说，我们讨论了熔融体的多孔流动集中到海中脊下方管道中的机制，以解释大多数海洋残余橄榄岩与海中脊玄武岩不平衡的现象。这种管道的存在也可以解释在暴露的地幔剖面中观察到的被称为替代溶质的地质特征。我们在这里通过线性分析表明，在存在溶解度梯度的情况下，化学反应性多孔介质中的流动是不稳定的，例如由大洋中脊下面的熔体绝热上升引起的溶解度梯度。最初均匀的流动在时间上集中，形成细长的高孔隙率手指，作为快速流动的熔体输送的管道。这种不稳定性是由一种正反馈机制引起的，其中孔隙度略高于平均孔隙度的区域导致非饱和流体流入增加，导致溶解增加，从而进一步降低孔隙度。即使在存在基质压实和化学扩散的情况下，这种不稳定性也被证明是稳健的。我们的分析还表明，存在着不断增长的行波，这些行波传递并放大了孔隙度和浓度的扰动。
We present results of a theoretical study aimed at understanding melt extraction from the upper mantle. Specifically, we address mechanisms for focusing of porous flow of melt into conduits beneath mid-ocean ridges in order to explain the observation that most oceanic residual peridotites are not in equilibrium with mid-ocean ridge basalt. The existence of such conduits might also explain geological features, termed replacive dunites, that are observed in exposed mantle sections. We show here, by linear analysis, that flow in a chemically reactive porous media is unstable in the presence of a solubility gradient, such as induced by adiabatic ascent of melt underneath mid-ocean ridges. The initially homogeneous flow becomes focused in time to produce elongated high-porosity fingers that act as conduits for transport of fast flowing melt. This instability arises due to a positive feedback mechanism in which a region of slightly higher than average porosity causes increased influx of unsaturated flow, leading to increased dissolution which further reduces the porosity. Even in the presence of matrix compaction and chemical diffusion the instability is demonstrated to be robust. Our analysis also indicates the existence of growing, traveling waves which transport and amplify porosity and concentration perturbations.