Pancakelike domes on Venus
Pancakelike domes on Venus
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金星上的煎饼状圆顶
DOI：
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
G. Pettengill
中科院分区：
文献类型：
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作者：
D. McKenzie;P. Ford;Fang Liu;G. Pettengill
将金星平原上七个大圆顶的形状与轴对称重力流在刚性水平表面上传播的形状进行了比较，这些圆顶的体积在100到1000千米之间。在合成孔径雷达图像上，圆顶交线的高度剖面和水平投影与牛顿流体的理论相似解符合得很好，但与刚塑性流变学计算的形状不同，也与具有强皮肤的静态模型的形状不同。当粘性电流扩散时，它产生一个各向同性的应变率张量，其大小与半径无关。这种流动可以解释圆顶表面均匀分布的随机定向裂纹。在下面的平原材料中流动所产生的应力很可能大到足以在穹顶以外的平原表面产生短径向裂缝。如果只有当流体是热的并且在1014Pa1017PaS之间时，才能进行扩散，则可以根据它们的热时间常数来估计穹顶的粘度。实验室实验表明，这种粘度对应于干燥流纹岩岩浆中610°到700°C的温度。这些温度与实验室测量的湿流纹岩的固相线温度一致。这些结果表明，可以用简单的流体动力学观点来理解穹隆的发展，所涉及的岩浆可以在10公里以下的深度湿熔融，然后喷发和脱气。
The shape of seven large domes on the plains of Venus, with volumes between 100 and 1000 km3, is compared with that of an axisymmetric gravity current spreading over a rigid horizontal surface. Both the altimetric profiles and the horizontal projection of the line of intersection of domes on the synthetic aperture radar images agree well with the theoretical similarity solution for a Newtonian fluid but not with the shape calculated for a rigid-plastic rheology nor with that for a static model with a strong skin. As a viscous current spreads, it generates an isotropic strain rate tensor whose magnitude is independent of radius. Such a flow can account for the randomly oriented cracks that are uniformly distributed on the surface of the domes. The stress induced by the flow in the plains material below is obtained and is probably large enough to produce the short radial cracks in the surface of the plains beyond the domes. The viscosity of the domes can be estimated from their thermal time constants if spreading is possible only when the fluid is hot and lies between 1014 and 1017 Pa s. Laboratory experiments show that such viscosities correspond to temperatures of 610° to 700°C in dry rhyolitic magmas. These temperatures agree with laboratory measurements of the solidus temperature of wet rhyolite. These results show that the development of the domes can be understood using simple fluid dynamical ideas and that the magmas involved can be produced by wet melting at depths below 10 km, followed by eruption and degassing.