华北地幔捕虏体Fe-Mg-Ca同位素研究进展

近年来,得益于同位素分析技术和质谱仪器性能的提高,使得铁（Fe）、镁（Mg）和钙（Ca）等非传统稳定同位素的高精度测量成为可能,并很快在地球化学、天体化学和生物地球化学等研究领域取得了丰硕的成果。本文通过对比分析来自华北克拉通不同地区不同类型地幔捕虏体的Fe、Mg和Ca位素组成特征,揭示华北克拉通岩石圈地幔Fe、Mg和Ca同位素组成不均一性的成因,并在此基础上,探讨华北大陆岩石圈地幔演化过程如部分熔融、橄榄岩-熔体反应过程、熔体的性质和来源等科学问题,为华北克拉通岩石圈的演化过程提供新证据。

     

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Partial derivatives of surface wave phase velocities for flat anisotropic models

Summary. Surface wave behaviour in flat anisotropic structures is first illustrated by performing an exact computation on a simple two-layer model. The variational procedure of Smith & Dahlen is then used to compute the partial derivatives of surface wave phase velocities with respect to the elastic parameters in more realistic earth models. Linear relationships between the partial derivatives for a general anisotropic structure and those for a transversely isotropic structure are derived. When considering waves propagating in a fixed direction, there are only four independent derivatives for Rayleigh waves, and two for Love waves. To avoid the lack of resolution in an inverse method, we propose to use physically constrained models. These results are illustrated by using a model with hexagonal symmetry and a symmetry axis oriented either vertically or horizontally. Quasi-Love- and quasi-Rayleigh-wave partial derivatives are computed for both axis orientations. Modes up to the second overtone and periods ranging between 45 and 130 s have been considered. Finally, anomalies of phase velocity are computed in an oceanic model made of 1/6 oriented olivine crystals with horizontal or vertical preferred orientations of the a -axis.     

Three-dimensional image of the anisotropic bodies beneath central Honshu, Japan

Shear-wave splitting from local deep earthquakes is investigated to clarify the volume and the location of two anisotropic bodies in the mantle wedge beneath central Honshu, Japan. We observe a spatial variation in splitting parameters depending on the combination of sources and receivers, nearly N–S fast in the northern region, nearly E–W fast in the southern region and small time delays in the eastern region. Using forward modelling, two models with 30 and 10 per cent anisotropy are tested by means of a global search for the locations of anisotropic bodies with various volumes. The optimum model is obtained for 30 per cent anisotropy, which means a 5 per cent velocity difference between fast and slow polarized waves. The northern anisotropic body has a volume of 1.00° (longitude) × 0.5° (latitude) × 75 km (depth), with the orientation of the symmetry axis being N20°E. The southern anisotropic body has a volume of 1.25° × 1.25° × 100 km with the symmetry axis along N95°E. Our results show that the anisotropic bodies are located in low-velocity and low- Q regions of the mantle. This, together with petrological data and the location of volcanoes in the arc, suggests that the possible cause of the anisotropy is the preferred alignment of cracks filled with melt.     

由PREM地球模型计算的洛夫数

本文选取迄今为止最完善的地球模型ＰＲＥＭ,利用它所定义的地球内部基本间断面及所给物质密度的弹性等参数分布,通过求解弹性地幔运动方程,得到形变位移矢量,由此计算出二阶洛夫数。本文的理论值与观测结果符合良好。