Abstract Over the last decade, seismological studies have shed new light on the properties of the mantle lithosphere and their physical and chemical origins. This paper synthesizes recent work to draw comparisons between oceanic and continental lithosphere, with a particular focus on isotropic velocity structure and its implications for mantle temperature and partial melt. In the oceans, many observations of scattered and reflected body waves indicate velocity contrasts whose depths follow an age-dependent trend. New modeling of fundamental mode Rayleigh waves from the Pacific ocean indicates that cooling plate models with asymptotic plate thicknesses of 85-95 km provide the best overall fits to phase velocities at periods of 25 s to 250 s. These thermal models are broadly consistent with the depths of scattered and reflected body wave observations, and with oceanic heat flow data. However, the lithosphere-asthenosphere velocity gradients for 85-95 km asymptotic plate thicknesses are too gradual to generate observable Sp phases, both at ages less than 30 Ma and at ages of 80 Ma or more. To jointly explain Rayleigh wave, scattered and reflected body waves and heat flow data, we propose that oceanic lithosphere can be characterized as a thermal boundary layer with an asymptotic thickness of 85-95 km, but that this layer contains other features, such as zones of partial melt from hydrated or carbonated asthenosphere, that enhance the lithosphere-asthenosphere velocity gradient. Beneath young continental lithosphere, surface wave constraints on lithospheric thickness are also compatible with the depths of lithosphere-asthenosphere velocity gradients implied by converted and scattered body waves. However, typical steady-state conductive models consistent with continental heat flow produce thermal and velocity gradients that are too gradual in depth to produce observed converted and scattered body waves. Unless lithospheric isotherms are concentrated in depth by mantle upwelling or convective removal, the presence of an additional factor, such as partial melt at the base of the thermal lithosphere, is needed to sharpen lithosphere-asthenosphere velocity gradients in young continental regions. Beneath cratons, numerous body wave conversions and reflections are observed within the thick mantle lithosphere, but the velocity layering they imply appears to be laterally discontinuous. The nature of cratonic lithosphere-asthenosphere velocity gradients remains uncertain, with some studies indicating gradual transitions that are consistent with steady-state thermal models, and other studies inferring more vertically localized velocity gradients.

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大洋和大陆地幔岩石圈的比较

摘要 在过去十年中，地震学研究为地幔岩石圈的性质及其物理和化学起源提供了新的线索。本文综合了最近的工作，以比较海洋和大陆岩石圈，特别关注各向同性速度结构及其对地幔温度和部分融化的影响。在海洋中，对散射体波和反射体波的许多观察表明速度对比的深度遵循与年龄相关的趋势。来自太平洋的基本模式瑞利波的新模型表明，渐近板厚度为 85-95 公里的冷却板模型提供了对 25 秒至 250 秒周期内相速度的最佳整体拟合。这些热模型与散射和反射体波观测的深度以及海洋热流数据大体一致。然而，85-95 公里渐近板块厚度的岩石圈-软流圈速度梯度太平缓，无法在年龄小于 30 Ma 和年龄大于 80 Ma 时产生可观测的 Sp 相。为了共同解释瑞利波、散射体波和反射体波以及热流数据，我们提出海洋岩石圈可以表征为渐近厚度为 85-95 公里的热边界层，但该层包含其他特征，例如带来自水合或碳酸化软流圈的部分熔体，这增强了岩石圈-软流圈速度梯度。在年轻的大陆岩石圈之下，对岩石圈厚度的表面波约束也与转换和散射体波所暗示的岩石圈-软流圈速度梯度的深度兼容。然而，与大陆热流一致的典型稳态传导模型产生的热梯度和速度梯度在深度上过于平缓，无法产生观察到的转换和散射体波。除非岩石圈等温线因地幔上涌或对流移除而在深处集中，否则需要存在额外的因素，例如热岩石圈底部的部分熔融，以锐化年轻大陆地区的岩石圈-软流圈速度梯度。在克拉通之下，在厚厚的地幔岩石圈中观察到了大量的体波转换和反射，但它们所暗示的速度分层似乎是横向不连续的。克拉通岩石圈-软流圈速度梯度的性质仍然不确定，一些研究表明逐渐转变与稳态热模型一致，而其他研究则推断出更多的垂直局部速度梯度。