Crustal S-velocity structure and radial anisotropy beneath the southern part of central and western North China Craton and the adjacent Qilian Orogenic Belt from ambient noise tomography
Crustal S-velocity structure and radial anisotropy beneath the southern part of central and western North China Craton and the adjacent Qilian Orogenic Belt from ambient noise tomography
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DOI：
10.1007/s11430-017-9092-8
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发表时间：
2017-09
期刊：
影响因子：
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通讯作者：
Y. Ling;Ling Chen;Zigen Wei;M. Jiang;Xu Wang
中科院分区：
文献类型：
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作者：
Y. Ling;Ling Chen;Zigen Wei;M. Jiang;Xu Wang
利用近一年的环境噪声层析成像资料，研究了由64个宽频带地震台站组成的密集线性便携式地震台阵的地壳S波速度结构和径向各向异性沿着分布。该阵列自东向西横穿华北中部造山带南部和华北西部造山带西部，到达邻近的祁连造山带。测量了5-35 s的瑞利波和5-30 s的Love波的相速度结构。利用莫霍面深度和地壳平均Vp/Vs比值的先验信息，通过逐点线性反演的频散数据（分别为Rayleigh波和Love波），构造了地壳S速度结构（VsvandVsh）。沿剖面的径向各向异性沿着是基于Vsh和Vsh之间的差异2×（Vsh−Vsv）/（Vsh+Vsv）计算的。结果表明，在三个主要构造单元中，构造变化明显。CNCC南部地壳结构复杂，低速带分布广泛，可能是中新生代构造和岩浆活动对地壳改造的反映。晋陕裂谷及邻区下地壳最低层具有明显的正径向各向异性，这可能是中新生代构造活化过程中地幔镁铁-超镁铁物质底侵作用的结果。鄂尔多斯南部中、下地壳整体速度横向变化较弱，速度相对较高，且存在大范围的正向径向各向异性，这可能反映了现今地壳结构仍保持着前寒武纪的构造特征。鄂尔多斯地块低速西倾沉积地层的形成与中生代盆地整体掀斜和晚白垩世以来不均匀剥蚀有关。结合前人的研究成果，对华北-西北CC南、北方地壳结构进行了系统的对比。这种异同可能与华北克拉通古元古代拼合前后所经历的构造事件和变形历史有关。QOB南部近平坦的中地壳低剪切带向东逐渐减弱，这可能与青藏高原向北东隆升扩张引起的强烈挤压体制下的地壳垂直叠加和韧性剪切变形有关。
The crustal S-velocity structure and radial anisotropy along a dense linear portable seismic array with 64 broadband seismic stations were investigated from ambient noise tomography with about one-year-long ambient noise recordings. The array transverses the southern part of the central North China Craton (CNCC) and western NCC (WNCC) from east to west and reaches the adjacent Qilian Orogenic Belt (QOB). The phase velocity structures of Rayleigh waves at 5–35 s and Love waves at 5–30 s were measured. The crustal S-velocity structures (VsvandVsh) were constructed from the dispersion data (Rayleigh and Love waves, respectively) from point-wise linear inversion with prior information of the Moho depth and average crustalVp/Vsratio. The radial anisotropy along the profile was calculated based on the discrepancies betweenVsvandVshas 2×(Vsh−Vsv)/(Vsh+Vsv). The results show distinct structural variations in the three major tectonic units. The crustal architecture in the southern CNCC is complicated and featured with wide-distributed low-velocity zones (LVZs), which may be a reflection of crustal modification resulting from Mesozoic-Cenozoic tectonics and magmatic activities. The pronounced positive radial anisotropy in the lower-lowermost crust beneath the Shanxi-Shaanxi Rift and the neighboring areas could be attributed to the underplating of mantle mafic-ultramafic materials during the Mesozoic-Cenozoic tectonic activation. In southern Ordos, the overall weak lateral velocity variations, relative high velocity and large-scale positive radial anisotropy in mid-lower crust probably suggest that the current crustal structure has preserved its Precambrian tectonic characteristics. The low-velocity westward-dipping sedimentary strata in the Ordos Block could be attributed to the Phanerozoic whole-basin tilting and the uneven erosion since late Cretaceous. Integrated with previous studies, the systematic comparison of crustal architecture was made between the southern and northern part of CNCC-WNCC. The similarities and differences may have a relation with the tectonic events and deformation histories experienced before and after the Paleoproterozoic amalgamation of the NCC. The nearly flat mid-crustal LVZ beneath the southern QOB weakens gradually as it extends to the east, which is a feature probably associated with crustal vertical superpositionand ductile shear deformation under the intensive compressional regime due to the northeastward growth and expansion of the Tibetan Plateau.