Local modification of the lithosphere beneath the central and western North China Craton : 3-D constraints from Rayleigh wave tomography
Local modification of the lithosphere beneath the central and western North China Craton : 3-D constraints from Rayleigh wave tomography
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DOI：
10.1016/j.gr.2012.06.018
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发表时间：
2013-11
影响因子：
6.1
通讯作者：
M. Jiang;Y. Ai;Ling Chen;Yingjie Yang
中科院分区：
文献类型：
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作者：
M. Jiang;Y. Ai;Ling Chen;Yingjie Yang
我们利用瑞利波层析成像技术对华北克拉通中西部的岩石圈结构进行了成像。使用 208 个宽带站记录的 100 个远震事件的瑞利波形来生成从 20 秒到 143 秒的 13 个周期的高分辨率相速度图。基于相速度图构建了 3-D 横波速度模型。我们的横波速度模型与之前的断层扫描研究结果大致一致，但显示了岩石圈内更详细的变化。跨华北造山带（TNCO）总体上以低速异常为特征，但表现出极大的非均质性。分别在北部和南部观察到两个主要的低速区（LVZ）。北部 LVZ 横向与新生代岩浆活动地点重合，延伸深度超过 200 公里。我们认为存在小规模的地幔上升流，仅限于 TNCO 的北部。在邻近新生代山西裂谷（SSR）狭窄转张带的两个 LVZ 之间也观察到了最上地幔的高速斑块。我们将其解释为克拉通地幔根的残余物。华北克拉通西部的鄂尔多斯地块与高速异常有关，同样反映了克拉通地幔根的存在，但在该位置100-150公里深度处观察到了可辨别的低速层。我们认为这种岩石圈中部结构可能是华北克拉通早期形成过程中交代过程形成的。根据我们的 S 波速度模型的观测结果，我们得出结论，当前 TNCO 下方高度不均匀的岩石圈结构是自克拉通合并以来对预先存在的机械薄弱区域进行多相改造的结果。最新的新生代岩石圈改造主要由太平洋板块俯冲和印度-欧亚大陆碰撞的远场效应主导。
We have imaged the lithospheric structure beneath the central and western North China Craton (NCC) with Rayleigh wave tomography. The Rayleigh waveforms of 100 teleseismic events recorded by 208 broadband stations are used to yield high-resolution phase velocity maps at 13 periods from 20 s to 143 s. A 3-D S-wave velocity model is constructed based on the phase velocity maps. Our S-wave velocity model is broadly consistent with the results of previous tomography studies, but shows more detailed variations within the lithosphere. The Trans-North China Orogen (TNCO) is generally characterized by low-velocity anomalies but exhibits great heterogeneities. Two major low-velocity zones (LVZs) are observed in the north and south, respectively. The northern LVZ laterally coincides with sites of Cenozoic magmatism and extends to depths greater than 200 km. We propose that a small-scale mantle upwelling is present, confined to the north of the TNCO. A high-velocity patch in the uppermost mantle is also observed between the two LVZs adjacent to the narrow transtensional zone of the Cenozoic Shanxi–Shaanxi Rift (SSR). We interpret this as the remnant of a cratonic mantle root. The Ordos Block in the western NCC is associated with high-velocity anomalies, similarly reflecting the existence of cratonic mantle root, but a discernible low-velocity layer is observed at depths of 100–150 km in this location. We interpret that this mid-lithospheric structure was probably formed by metasomatic processes during the early formation of the NCC. Based on the observations from our S-wave velocity model, we conclude that the current highly heterogeneous lithospheric structure beneath the TNCO is the result of multiphase reworking of pre-existing mechanically weak zones since the amalgamation of the craton. The latest Cenozoic lithospheric reworking is dominated by the far-field effects of both Pacific plate subduction and the India–Eurasia collision.