On the effect of temperature and strain-rate dependent viscosity on global mantle flow, net rotation, and plate-driving forces
On the effect of temperature and strain-rate dependent viscosity on global mantle flow, net rotation, and plate-driving forces
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DOI：
10.1111/j.1365-246x.2006.03172.x
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发表时间：
2006-11-01
影响因子：
2.8
通讯作者：
Becker, Thorsten W.
中科院分区：
文献类型：
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作者：
Becker, Thorsten W.
全球环流模型进行了分析，使用温度和应变率依赖流变学，以完善以前的估计地幔流和板块驱动力的性质。根据构造模型和地震层析成像推断的温度，海洋下的粘度比大陆下面的粘度低一个数量级。如果净旋转的岩石圈相对于一个稳定的下地幔参考框架占，在上地幔的流动模式是相似的分层模型和那些横向变化的粘度。激发净旋转尺度的粘度对比大陆根的环境地幔，这种对比是动态的幂律流变学的限制。曲面净旋转与热点参考坐标系欧拉极点的方向匹配良好，并且幅度具有正确的数量级。我比较规定的表面速度模型与自由滑动计算与施加在板边界的薄弱区，速度场一般是一致的。基于实验室蠕变规律的干橄榄石模型被证明是兼容的平均径向粘度分布，板块速度的方向和幅度，板状表面速度，环形：极向分区，构造各向异性的形成下位错蠕变在上地幔。包括温度相关的变化增加了海洋与大陆岩石圈的相对速度，使表面速度更像板块，并提高了一般适合观察到的板块运动。这些研究结果意味着板块驱动力的研究是基于简单的地幔流变学可能需要重新审视。
Global circulation models are analysed using a temperature and strain-rate dependent rheology in order to refine previous estimates of the nature of mantle flow and plate driving forces. Based on temperature inferred from a tectonic model and seismic tomography, the suboceanic viscosity is lower than underneath continents by similar to one order of magnitude. If net-rotations of the lithosphere with respect to a stable lower mantle reference frame are accounted for, the patterns of flow in the upper mantle are similar between models with layered and those with laterally varying viscosity. The excited net rotations scale with the viscosity contrast of continental roots to the ambient mantle; this contrast is dynamically limited by the power-law rheology. Surface net rotations match the orientation of hotspot reference-frame Euler poles well, and amplitudes are of the right order of magnitude. I compare prescribed surface velocity models with free-slip computations with imposed weak zones at the plate boundaries; velocity fields are generally consistent. Models based on laboratory creep laws for dry olivine are shown to be compatible with average radial viscosity profiles, plate velocities in terms of orientation and amplitudes, plateness of surface velocities, toroidal:poloidal partitioning, and fabric anisotropy formation under dislocation creep in the upper mantle. Including temperature-dependent variations increases the relative speeds of oceanic versus continental lithosphere, makes surface velocities more plate-like, and improves the general fit to observed plate motions. These findings imply that plate-driving force studies which are based on simpler mantle rheologies may need to be revisited.