Crustal radial anisotropy beneath the Dabie orogenic belt from ambient noise tomography
Crustal radial anisotropy beneath the Dabie orogenic belt from ambient noise tomography
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DOI：
10.1093/gji/ggt281
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发表时间：
2013-11
影响因子：
2.8
通讯作者：
Yinhe Luo;Yixian Xu;Yingjie Yang
中科院分区：
文献类型：
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作者：
Yinhe Luo;Yixian Xu;Yingjie Yang
摘要在本研究中，我们继续之前的各向同性剪切速度成像工作，通过联合分析瑞利波和洛夫波频散曲线来研究大别造山带及其周边地区地壳径向各向异性。除了处理垂直分量数据以检索瑞利波之外，我们还收集水平分量连续环境噪声数据，并从站对之间水平分量噪声数据的互相关中检索洛夫波。然后，我们使用谱方法测量 8 至 35 s 周期的 Love 相速度色散曲线，并进行表面波断层扫描以获得高分辨率相速度图。最后，我们通过反演瑞利波和洛夫波的局部相速度色散曲线来确定地壳径向各向异性。我们的地壳径向各向异性模型揭示了与华北克拉通和扬子克拉通之间的大陆碰撞动态过程和碰撞后改造相关的复杂各向异性模式。华北盆地整个地壳径向各向异性均为正值，对应于中生代以来伸展构造发育的区域。在江汉盆地中下地壳中观察到强烈的正径向各向异性，这很可能是由于地壳伸展变形作用下地震各向异性物质的近水平排列所致。在大别造山带东部，北大别杂岩（NDC）下地壳的径向各向异性在上下地壳中呈正值，在中地壳中呈负值。上地壳的正径向各向异性可能是由于在火成岩挤压和侵位过程中的拉张构造作用下存在各向异性矿物呈近水平排列的火成岩，而下地壳的正径向各向异性可能是由于造山运动拆沉后岩浆底侵引起的各向异性物质形成近水平排列。在中地壳中，与深部岩浆垂直侵入相关的有限应变可能会导致晶体各向异性矿物垂直排列，从而导致观察到的负径向各向异性。大别造山带西部除红安超高压区以下中地壳径向各向异性为负值外，整个地壳均存在正径向各向异性。与NDC类似，红安超高压可能经历了与大别东部相似的热地球动力过程，负径向各向异性也可能是深部岩浆垂直侵入导致各向异性矿物垂直排列的结果。在信阳地区的中地壳中成像显示出强烈的局部负径向各向异性，这很可能是由于火山活动期间来自上地幔的垂直侵入的镁铁质岩浆结晶而成的各向异性矿物的垂直排列造成的。
SUMMARY In this study, we continue our previous work of imaging isotropic shear velocity to study the crustal radial anisotropy beneath the Dabie orogen and surrounding regions by jointly analysing Rayleigh wave and Love wave dispersion curves. In addition to processing the vertical component data to retrieve Rayleigh waves, we collect horizontal-component continuous ambient noise data and retrieve Love waves from cross-correlations of horizontal-component noise data between station pairs. Then, we measure Love phase velocity dispersion curves at periods from 8 to 35 s using a spectral method and perform surface wave tomography to obtain high-resolution phase velocity maps. Finally, we determine crustal radial anisotropy by inverting the local phase velocity dispersion curves of Rayleigh and Love waves. Our model of crustal radial anisotropy reveals complex anisotropic patterns associated with the dynamic processes of continent–continent collisions and post-collision reworking between the North China Craton and the Yangtze Craton. In the Huabei Basin, the radial anisotropy is positive throughout the entire crust, corresponding to areas with extensional tectonics developed since the middle Mesozoic. In the Jianghan Basin, strong positive radial anisotropy in the middle and lower crust is observed, most likely resulting from subhorizontal alignment of seismic anisotropic materials under the crustal extensional deformation. In the eastern Dabie orogenic belt, the radial anisotropy beneath Northern Dabie complex (NDC) appears positive in the upper and lower crust and negative in the middle crust. The positive radial anisotropy in the upper crust is probably because of the presence of igneous rocks with anisotropic minerals aligned subhorizontally under the action of the extensional tectonics during igneous extrusion and emplacement, whereas the positive radial anisotropy in the lower crust is probably because that subhorizontal alignment of anisotropic materials induced by magmatic underplating formed after the delamination of the orogeny. In the middle crust, finite strains associated with the vertical intrusion of deep magma might cause crystalline anisotropic minerals aligned vertically, resulting in observed negative radial anisotropy. In the western Dabie orogenic belt, positive radial anisotropy is present in the whole crust except beneath the Hong’an ultrahigh pressure (UHP) area where radial anisotropy is negative in the middle crust. Similar to NDC, the Hong’an UHP probably experienced similar thermal geodynamic processes as the eastern Dabie and the negative radial anisotropy might be also the result of vertical alignment of anisotropic minerals caused by the vertical intrusion of deep magma. Strong localized negative radial anisotropy in the middle crust beneath the Xinyang area is imaged, most likely caused by the vertical alignment of anisotropic minerals crystallized from the vertically intruding mafic magma originated from the upper mantle during the volcanism.