Insights into layering in the cratonic lithosphere beneath Western Australia
Insights into layering in the cratonic lithosphere beneath Western Australia
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深入了解西澳大利亚下方克拉通岩石圈的分层
DOI：
10.1002/2017jb014904
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Zhao Liang
中科院分区：
文献类型：
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作者：
Sun Weijia;Fu Li-Yun;Saygin Erdinc;Zhao Liang
岩石圈内部结构面的特征承载着岩石圈起源和演化的重要信息。然而，岩石圈中部不连续面（MLD）的形成和机制仍然是一个谜和争议。我们调查了太古代西澳大利亚州的岩石圈中部的不连续性，这代表了地球仪上最古老的大陆之一，使用一种新的接收器为基础的反射率的方法结合其他地球物理信息，包括层析P和S波速度，径向各向异性，电阻率和热流数据。MLD相当浅，深度为68-82 km。使用构造的高频（0.5-4 Hz）P波反射率在岩石圈地幔中观察到多个显著的不连续性。这些多个不连续面与岩石圈到软流圈渐变过渡带顶部的相对P波和SV波速度的大范围降低相吻合。上岩石圈地幔的强径向各向异性在MLD上趋于弱，这可能反映了水平相关长度大于垂直相关长度的准层状岩石圈非均匀性行为。宽尺度电阻率变化与MLD几乎没有一致性。鉴于这些不同的地球物理观测，上部岩石圈表现出刚性和弹性的MLD以上的属性，而较低的岩石圈往往是韧性和流变或粘性。一个包含准层状岩石圈非均匀性的模型可以有效地代表太古代大陆之下的MLD特征。
The characteristics of internal lithospheric discontinuities carry crucial information regarding the origin and evolution of the lithosphere. However, the formation and mechanisms of the midlithosphere discontinuity (MLD) are still enigmatic and controversial. We investigate the midlithospheric discontinuities beneath the Archean Western Australian Craton, which represents one of the oldest continents on the globe, using a novel receiver‐based reflectivity approach combined with other geophysical information comprising tomographic P and S wave velocity, radial anisotropy, electrical resistivity, and heat flow data. The MLD is rather shallow with a depth of 68–82 km. Multiple prominent discontinuities are observed in the lithospheric mantle using constructed high‐frequency (0.5–4 Hz) P wave reflectivities. These multiple discontinuities coincide well with the broad‐scale reduction of relative P and SV wave velocities at the top of the graded transition zone from the lithosphere to the asthenosphere. Strong radial anisotropy in the upper lithosphere mantle tends to be weak across the MLD, which might reflect quasi‐laminar lithospheric heterogeneity behavior with a horizontal correlation length that is greater than its vertical correlation length. Broad‐scale electrical resistivity variations show little coherence with the MLD. Given these various geophysical observations, the upper lithosphere exhibits rigid and elastic properties above the MLD, while the lower lithosphere tends to be ductile and rheological or viscous. A model comprising quasi‐laminar lithospheric heterogeneity could effectively represent the MLD characteristics beneath the Archean continent.