On the fate of thermally buoyant mantle plumes at density interfaces
On the fate of thermally buoyant mantle plumes at density interfaces
复制标题
DOI：
10.1016/j.epsl.2006.11.029
复制
发表时间：
2007-02
影响因子：
5.3
通讯作者：
I. Kumagai;A. Davaille;K. Kurita
中科院分区：
文献类型：
--
作者：
I. Kumagai;A. Davaille;K. Kurita
660公里深的吸热相变预计将推迟上涌羽流并改变它们的形态。利用温度、成分和速度场的同时可视化，对热启动羽流与密度边界的相互作用进行了实验研究。在一个由两种不同密度和粘度的粘性流体组成的储罐中，通过在储罐底部使用圆板加热器产生热启动羽流。它与内界面的相互作用模式取决于局部浮力数(BL：界面稳定化学浮力与羽流热浮力之比)、瑞利数(Ra)、化学层间的粘度差(γ)和周围物质与羽流头部的局部粘度比(γp)。对于BL<；0.6，由于与两层之间稳定的密度对比相比，羽流头部具有很大的热浮力，因此形成了“穿透模式”，即大量的下层材料通过上层上升并到达顶部表面。当BL>；0.6时，出现“重生模式”，热羽在化学边界下汇聚和扩散，二次热羽从界面产生。根据边界层的大小，这些羽状物可以通过粘性耦合相当数量的低层物质而向上卷进。确定了二次羽流的开始、它们的数量和波长、夹带量和界面的地形的标度定律。我们的结果可以解释超井以上的热点分布和留尼汪岛热点的特殊时间演化。
The 660-km depth endothermic phase transition is expected to delay upwelling plumes and modify their morphology. The interaction of thermal starting plumes with a density boundary is investigated experimentally by using simultaneous visualizations of temperature, composition and velocity fields. In a tank initially stratified with two viscous fluids with different densities and viscosities, a thermal starting plume was generated by using a circular plate heater at the bottom of the tank. Its interaction mode with the inner interface depends on the local buoyancy number (BL: the ratio of the stabilizing chemical buoyancy to the plume thermal buoyancy at the interface), the Rayleigh number (Ra), the viscosity contrast between the chemical layers (γ), and the local viscosity ratio of the ambient material to the plume head (γp). For BL<0.6, the “pass-through mode” develops, whereby a large volume of the lower material rises through the upper layer and reaches the top surface, since the plume head has a large thermal buoyancy compared to the stabilizing density contrast between the two layers. When BL>0.6, the “rebirth mode” occurs, where the thermal plume ponds and spreads under the chemical boundary and secondary thermal plumes are generated from the interface. Depending on the magnitude of BL, these plumes can entrain upwards by viscous coupling a significant amount of lower layer material. Scaling laws are determined for the onset of secondary plumes, their number and wavelength, the amount of entrainment and the topography of the interface. Our results could explain the hotspots' distribution above superswells and the peculiar time evolution of La Réunion hotspot.