Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin
Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin
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DOI：
10.1016/j.tecto.2006.01.025
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发表时间：
2005-12
期刊：
影响因子：
2.9
通讯作者：
Mingjun Liu;W. Mooney;Songlin Li;N. Okaya;S. Detweiler
中科院分区：
文献类型：
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作者：
Mingjun Liu;W. Mooney;Songlin Li;N. Okaya;S. Detweiler
达日-兰州-靖边地震折射剖面位于青藏高原东北缘，长约1000 km。该剖面横跨北方松潘-甘孜褶皱系、秦岭-祁连褶皱系、海原弧形构造区和稳定的鄂尔多斯盆地。纵、横波速度结构和泊松比在剖面上显示出许多显著的特征。地壳厚度由东北向西南逐渐增加。地壳平均厚度从鄂尔多斯盆地的42 km增加到松潘-甘孜盆地的63 km。海原断裂以南、西秦岭以下地壳明显增厚。地壳速度沿剖面沿着有明显的变化。结晶地壳的平均P波速度在6.3和6.4 km/s之间变化。松潘-甘孜、西秦岭和海原弧形构造区P波速度为6.3km/s，比世界平均值6.45km/s低0.15km/s。昆仑断裂以北，除海原弧形构造区外，P波平均速度为6.4km/s，仅比世界平均值低0.5km/s。组合的P波速度和泊松比表明，地壳主要是长英质的组合物与中间组合物在基地。青藏高原东北缘松潘-甘孜盆地至鄂尔多斯盆地缺乏镁铁质下地壳。西秦岭和海原弧形构造区存在低速带。低速区具有低的S波速度和高的泊松比，因此这些区域可能是由于部分熔融。地壳分为上、下两层，随着向青藏高原东北部的靠近，地壳增厚主要发生在下地壳。研究结果表明，随着地壳厚度的增加，下地壳厚度从22 km增加到38 km，从鄂尔多斯盆地的42 km增加到昆仑断裂以南的松潘-甘孜盆地的63 km。西秦岭和海原弧形构造区的康拉德不连续面和莫霍面均为层状界面，显示出强烈的构造活动。海原弧形构造区的弧形断裂和大地震是青藏高原与中朝地台和戈壁-阿拉山地台相互作用的结果。
The 1000-km-long Darlag–Lanzhou–Jingbian seismic refraction profile is located in the NE margin of the Tibetan plateau. This profile crosses the northern Songpan-Ganzi terrane, the Qinling-Qilian fold system, the Haiyuan arcuate tectonic region, and the stable Ordos basin. The P-wave and S-wave velocity structure and Poisson's ratios reveal many significant characteristics in the profile. The crustal thickness increases from northeast to southwest. The average crustal thickness observed increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane. The crust becomes obviously thicker south of the Haiyuan fault and beneath the West-Qinlin Shan. The crustal velocities have significant variations along the profile. The average P-wave velocities for the crystalline crust vary between 6.3 and 6.4 km/s. Beneath the Songpan-Ganzi terrane, West-Qinling Shan, and Haiyuan arcuate tectonic region P-wave velocities of 6.3 km/s are 0.15 km/s lower than the worldwide average of 6.45 km/s. North of the Kunlun fault, with exclusion of the Haiyuan arcuate tectonic region, the average P-wave velocity is 6.4 km/s and only 0.5 km/s lower than the worldwide average. A combination of the P-wave velocity and Poisson's ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base. A mafic lower crust is absent in the NE margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin. There are low velocity zones in the West-Qinling Shan and the Haiyuan arcuate tectonic region. The low velocity zones have low S-wave velocities and high Poisson's ratios, so it is possible these zones are due to partial melting. The crust is divided into two layers, the upper and the lower crust, with crustal thickening mainly in the lower crust as the NE Tibetan plateau is approached. The results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane south of the Kunlun fault. Both the Conrad discontinuity and Moho in the West-Qinling Shan and in the Haiyuan arcuate tectonic region are laminated interfaces, implying intense tectonic activity. The arcuate faults and large earthquakes in the Haiyuan arcuate tectonic region are the result of interaction between the Tibetan plateau and the Sino–Korean and Gobi Ala Shan platforms.