SUBDUCTED SLABS AND THE GEOID - CONSTRAINTS ON MANTLE RHEOLOGY AND FLOW
SUBDUCTED SLABS AND THE GEOID - CONSTRAINTS ON MANTLE RHEOLOGY AND FLOW
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DOI：
10.1029/jb089ib07p06003
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发表时间：
1984-01-01
影响因子：
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通讯作者：
HAGER, BH
中科院分区：
文献类型：
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作者：
HAGER, BH
大地水准面异常主要是密度差驱动地幔对流和板块运动的结果。在对流地球中，由给定的密度差引起的总大地水准面异常受与上表面和内部成分边界的流致变形相关的质量异常以及密度差本身的影响。这些边界变形，从而总的重力场，取决于径向分布的有效粘度。如果内部密度对比可以估计，是俯冲板的情况下，有用的约束可以放置在对流系统的深度和粘度随深度的变化。观测到的长波大地水准面的4-9度分量与地震活跃俯冲板的密度模型预测的分量高度相关。相关性的（正）符号要求有效粘度随深度增加30倍或更多。然而，这种相关性的幅度不能用与俯冲板块地震活跃部分相关的密度对比来解释。如果与俯冲有关的密度差延伸到下地幔，或者如果旧的岩石圈在俯冲带下方的上地幔底部堆积，在数千公里的水平距离上厚度超过350公里，则可以解释这种幅度。粘度随深度增加的地幔中的地幔对流提供了俯冲带上长波长大地水准面异常的简单解释。
Geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion. The total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow‐induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself. These boundary deformations, and hence the total gravity field, depend on the radial distribution of effective viscosity. If the internal density contrasts can be estimated, as is the case for subducted slabs, useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system. The degree 4–9 components of the observed long‐wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs. The (positive) sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more. The amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs, however. The amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers. Mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long‐wavelength geoid anomalies over subduction zones.