Glacial rebound of the British Isles—III. Constraints on mantle viscosity
Glacial rebound of the British Isles—III. Constraints on mantle viscosity
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不列颠群岛的冰川回弹——对地幔粘度的限制
DOI：
10.1111/j.1365-246x.1996.tb00003.x
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发表时间：
1996
影响因子：
2.8
通讯作者：
M. Nakada
中科院分区：
文献类型：
--
作者：
K. Lambeck;P. Johnston;C. Smither;M. Nakada
对上一次冰川盛期以来海平面变化的简要观测为地球对103-104年时间尺度上地表负荷变化的反应提供了重要的制约因素。这种响应可以方便地用一个或多个地幔的有效弹性岩石圈厚度和有效粘性来描述。描述这些层的参数之间可能会发生相当大的权衡，不同的组合可能会产生可比较的海平面变化预测。特别是，岩石圈厚度和上地幔粘度之间的权衡可能很重要，对于任何合理的岩石圈厚度值，都可以找到相应的地幔粘度结构，给出海平面预测与观测的可信比较。特别是，薄岩石圈模型将导致对上地幔粘度的低估计，而厚岩石圈模型将导致高粘性值。然而，任一解可能只表示模型参数空间中的局部最小值，并且可能不对应于最优解。因此，重要的是，在观测数据的反演中，在整个模型参数空间进行全面搜索，以确保确定的解确实与最佳解相对应。不列颠群岛的海平面数据非常适合这样的反演，因为数据的质量相对较高，数据相对于前冰盖有良好的地理分布，并且对前冰盖及其后退的尺寸有合理的观测限制。此外，由于远冰盖和融水负荷对海平面信号的贡献，该地区的观测数据库对深部地幔的粘性也具有一定的分辨率。所探索的参数空间由最多五个地幔、有效弹性厚度为Di的岩石圈和一系列分别向下延伸到200、400和670公里深度的上地幔(i=2-4)和一个向下延伸到核幔边界的粘性QLm的下地幔层来定义。所探索的参数范围为30<；D，I120千米，3×10~9 Iqi
SUMMARY Observations of sea-level change since the time of the last glacial maximum provide important constraints on the response of the Earth to changes in surface loading on time-scales of 103-104 years. This response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers. Considerable trade-off between the parameters describing these layers can occur, and different combinations can give rise to comparable predictions of sea-level change. In particular, the trade-off between lithospheric thickness and upper-mantle viscosity can be important, and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations. In particular, thin-lithosphere models will lead to low estimates for the upper-mantle viscosity, while thick-lithosphere models lead to high viscosity values. However, either solution may represent only a local minimum in the model parameter space, and may not correspond to the optimum solution. It becomes important, therefore, that in the inversion of observational data, a comprehensive search is conducted throughout the entire model-parameter space, to ensure that the solution identified does indeed correspond to the optimum solution. The sea-level data for the British Isles lend themselves well to such an inversion because of the relatively high quality of the data, the good geographic distribution of the data relative to the former ice sheet, and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat. Furthermore, because of the contribution to the sea-level signal from the distant ice sheets, as well as from the melt-water load, the observational data base for the region also has some resolving power for the viscosity of the deeper mantle. The parameter space explored is defined by up to five mantle layers, the lithosphere of effective elastic thickness D,, and a series of upper-mantle layers, i = 2-4, extending down to depths of 200, 400 and 670 km, respectively, each of viscosity qi, and a lower-mantle layer of viscosity qlm extending down to the coremantle boundary. The range of parameters explored is 30 < D, I 120 km, 3 x lOI9 Iqi