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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Hydrated subducted crust at 100-250 km depth
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Hydrated subducted crust at 100-250 km depth

机译：100-250 km深度的水合俯冲地壳

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摘要

Seismic waves that travel along the surface of subducted slabs provide a means to infer petrology to considerable depth. At high frequencies (0.5-10 Hz) they are particularly sensitive to the presence and state of subducted oceanic crust. New observations reveal systematic distortion of body waves in all north Pacific subduction zones, when signals traverse slabs at 100-250 km depths, suggesting that crust remains distinct to these depths. The signals show waveguide behavior at the scale of few kilometers: short-wavelength, high-frequency energy (≥3 Hz) is delayed 5-7% relative to that of low frequencies (≥1 Hz), systematically at all subduction zones. To explain these observations, velocities in a low-velocity layer 1-7 km thick, likely subducted crust, must remain seismically slow relative to surrounding mantle at these depths. Hence, it seems unlikely that subducted crust has completely converted to eclogite, as often assumed. Inferred velocities within subducted crust are similar to those estimated for blueschists, suggesting that hydrous assemblages persist past the volcanic front.
机译：沿着俯冲平板表面传播的地震波提供了一种将岩石学推论到相当深的方法。在高频（0.5-10 Hz）下，它们对俯冲洋壳的存在和状态特别敏感。新的观测结果显示，当信号在100-250 km的深度穿过平板时，北太平洋所有俯冲带中的体波都有系统的畸变，这表明地壳在这些深度处仍然不同。这些信号在几公里的尺度上显示出波导行为：在所有俯冲带，系统都将短波高频能量（≥3Hz）相对于低频（≥1Hz）延迟了5-7％。为了解释这些发现，相对于周围地幔在这些深度处，低速层（1-7公里厚，可能是俯冲的地壳）中的速度必须保持地震缓慢。因此，俯冲的地壳似乎不可能像通常所认为的那样完全转变成榴辉岩。俯冲的地壳内的推断速度与对蓝片岩估计的速度相似，表明水合体持续穿过火山前沿。

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