Three-dimensional forward and backward numerical modeling of mantle plume evolution: Effects of thermal diffusion
Three-dimensional forward and backward numerical modeling of mantle plume evolution: Effects of thermal diffusion
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地幔柱演化的三维正反演数值模拟：热扩散的影响
DOI：
10.1029/2005jb003782
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发表时间：
2006-06
影响因子：
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通讯作者：
A. Ismail-Zadeh;G. Schubert;I. Tsepelev;A. Korotkii
中科院分区：
文献类型：
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作者：
A. Ismail-Zadeh;G. Schubert;I. Tsepelev;A. Korotkii
通过三维数值模拟，研究了热扩散对地幔柱演化的影响。地幔柱是由热边界层的热的、低粘性的物质供给的。羽流的物质主要是平流输送到地球表面，并伴有一些热扩散效应。然而，随着时间的推移，馈送会变得越来越弱，然后热扩散可以接管并控制羽流的演变。数值实验表明，边界层热物质对地幔柱的一周补给导致地幔柱尾部先扩散消失，头部后扩散消失。这是最有可能的解释地震检测到的低速地幔结构（地幔柱）与突出的头部和几乎看不见的尾巴在中地幔深度。我们开发的恢复模型（在时间上向后），以恢复强大的功能，地幔柱在地质的过去，他们已经消散后，由于热扩散和热扩散和温度依赖的粘度对地幔柱的重建分析的影响。我们调查的热扩散对我们的恢复（变分数据同化）算法的性能的影响。对于一个给定的范围内的瑞利数Ra和两个值的粘度比r（模型域的上，下边界之间），我们表明：（1）之间的残差预测的温度和重建的反向模型变得更大，（2）恢复过程变得更差的Ra减少和r增加。我们同化的温度从高分辨率地震层析成像数据的东南喀尔巴阡山脉，并表明，目前的扩散地幔结构可以恢复到其突出的状态在中新世时代。我们讨论了模型输入和输出数据的平滑性问题，与建模相关的误差，以及地幔热对流数据同化中的一些其他挑战。
We investigate the effects of thermal diffusion on the evolution of mantle plumes by means of three-dimensional numerical modeling forward and backward in time. Mantle plumes are fed by a hot, low-viscous material from the thermal boundary layer. The material of the plumes is mainly advected toward the Earth's surface with some effects of thermal diffusion. However, the feeding can become weaker with time, and then thermal diffusion can take over and control the evolution of the plumes. Numerical experiments forward in time show that a week feeding of mantle plumes by the hot material from the boundary layer results in the diffusive disappearance of plume tails first and plume heads later. This is the most likely explanation for the seismically detected low-velocity mantle structures (mantle plumes) with prominent heads and almost invisible tails at midmantle depths. We develop restoration models (backward in time) to recover strong features of mantle plumes in the geological past after they have dissipated due to thermal diffusion and analyze effects of thermal diffusion and temperature-dependent viscosity on the reconstruction of the mantle plumes. We investigate the impact of thermal diffusion on the performance of our restoration (variational data assimilation) algorithm. For a given range of Rayleigh number Ra and two values of the viscosity ratio r (between the upper and lower boundaries of the model domain) we show that (1) the residuals between the temperature predicted by the forward model and that reconstructed by the backward modeling become larger and (2) the restoration process becomes poorer as Ra decreases and r increases. We assimilate temperature obtained from high-resolution seismic tomography data for the southeastern Carpathians and show that present diffused mantle structures can be restored to their prominent state in the Miocene times. We discuss the problems of smoothness of model input and output data, errors associated with the modeling, and some other challenges in the data assimilation for thermoconvective flow in the mantle.