Global Patterns in Cratonic Mid‐Lithospheric Discontinuities From Sp Receiver Functions
Global Patterns in Cratonic Mid‐Lithospheric Discontinuities From Sp Receiver Functions
复制标题
DOI：
10.1029/2021gc009819
复制
发表时间：
2021-06
期刊：
影响因子：
3.7
通讯作者：
H. E. Krueger;I. Gama;K. Fischer
中科院分区：
文献类型：
--
作者：
H. E. Krueger;I. Gama;K. Fischer
本研究的目的是限制克拉通地幔岩石圈内地震速度结构分层的起源（即中岩石圈不连续面 [MLD]）。对于全球克拉通中的长寿站，我们使用时域反卷积和 k 均值算法计算 S 到 P 转换的相位接收器函数堆栈，以选择稳健、一致的接收器函数。负 MLD 仅出现在 50% 的接收器功能堆栈中，表明负 MLD 很常见，但间歇性的。负 MLD 对应于 1%–4% 的剪切速度下降，这可能是由交代作用产生的矿物层引起的，尽管不能排除地震各向异性中的垂直分层。在克拉通内部，负 MLD 具有较低的幅度（<3% 速度下降），并且可以通过原始太古代地幔的交代作用来解释。负 MLD 振幅随着上地幔剪切速度（朝向克拉通外缘）的降低而增加，但不取决于克拉通的年龄。因此，负 MLD 振幅并不是由克拉通地幔成分的年龄相关变化主导，而是与克拉通形成后很长时间内发生的构造和交代活动的接近程度密切相关。在具有古元古代和太古代热构造年龄的台站中，负MLD数量较少，这与早期“暖”俯冲期间板片衍生流体的浅层释放不利于负MLD形成的观点一致。我们还在克拉通边界和内部的台站观测到低于 150 km 的速度梯度，表明克拉通岩石圈-软流圈边界和/或莱曼不连续处存在地震速度变化。
The goal of this study is to constrain the origins of layering in the seismic velocity structure within the cratonic mantle lithosphere (i.e. mid‐lithospheric discontinuities [MLDs]). For long‐lived stations in cratons worldwide, we calculated S‐to‐P converted phase receiver function stacks using time domain deconvolution and a k‐means algorithm to select robust, consistent receiver functions. Negative MLDs appear in only 50% of the receiver function stacks, indicating that negative MLDs are common but intermittent. The negative MLDs correspond to shear velocity drops of 1%–4%, which could be caused by layers of minerals created by metasomatism, although vertical layering in seismic anisotropy cannot be ruled out. In craton interiors, negative MLDs have a lower amplitude (<3% velocity drops) and can be explained by metasomatism of the original Archean mantle. Negative MLD amplitudes increase with decreasing upper mantle shear velocity (toward the outer margins of the cratons), but do not depend on the age of the craton. Thus, negative MLD amplitudes are not dominated by age‐related variations in the cratonic mantle composition, and, instead, are more strongly correlated with proximity to tectonic and metasomatic activity that occurred long after craton formation. Negative MLDs are less numerous among stations that have Paleoproterozoic and Archean thermotectonic ages, consistent with the view that shallow release of slab‐derived fluids during early “warm” subduction was less favorable for negative MLD formation. We also observe velocity gradients below 150 km at stations in craton boundaries and interiors, indicating the presence of seismic velocity changes at the cratonic lithosphere‐asthenosphere boundary and/or Lehmann discontinuity.