Crustal thickening and variations in architecture from the Qaidam basin to the Qang Tang (North-Central Tibetan Plateau) from wide-angle reflection seismology
Crustal thickening and variations in architecture from the Qaidam basin to the Qang Tang (North-Central Tibetan Plateau) from wide-angle reflection seismology
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DOI：
10.1016/j.tecto.2005.09.011
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发表时间：
2006-01
期刊：
影响因子：
2.9
通讯作者：
M. Jiang;A. Galve;A. Hirn;B. Voogd;M. Laigle;H. Su;Jordi Díaz;J. Lépine;Y. X. Wang
中科院分区：
文献类型：
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作者：
M. Jiang;A. Galve;A. Hirn;B. Voogd;M. Laigle;H. Su;Jordi Díaz;J. Lépine;Y. X. Wang
利用6个炮点，获得了藏东北700公里断面上地壳尺度的广角反射-折射剖面。通过侧面扇面记录和在线剖面采样的组合，我们可以成像到向高原中心方向增加的莫霍面深度。它们在北昆仑、巴彦哈尔和羌塘之间的两个块体边界上以不同的风格出现，地壳内部结构和地层速度的变化也表明了这一点。观测到了清晰的S波：它们与P波一起，罕见地制约了地壳单元的组成，揭示了整个地壳及其下半部沿整个断面的异常长石质平均组成。在北昆仑-柴达木地块上，发现地壳厚度的变化，莫霍面深度在55~65公里之间，与基底地形呈负相关。在巴彦哈尔地块北部，70公里厚的地壳中部表现出强烈的非均质性。根据合成地震图模拟，这可能是巴彦哈尔地壳向北构造叠加在北昆仑地壳的薄层包裹体的结果。根据扇形剖面的图像，相应的上部可能向北运移，从而也加厚了现在北昆仑地块的上地壳。在羌塘北部，得到了厚75公里的地壳和下半部地壳的模型，平均速度具有长英质成分的特征。从巴彦哈尔到羌塘，记录了金沙缝合带和鲜水河断裂从顺向和侧向记录到几个炮点的深部结构变化。与地壳下部的长英质成分一起，莫霍面偏移距表明巴彦哈尔地壳在羌塘岩石圈中处于南倾莫霍面和北倾莫霍面之间的叠置作用。原来较薄的巴彦哈尔地壳和岩石圈形成的羌塘凹陷模型，随着部分羌塘带到更深的深度，也将与扇形剖面所拍摄的从羌塘到巴彦哈尔过渡的莫霍面地形相一致。
Wide-angle reflection–refraction profiles at crustal scale have been obtained along a 700 km transect of northeastern Tibet from six shotpoints. A combination of sampling by broadside fan-recordings and in-line profiling allows us to image increases in Moho depth towards the centre of the plateau. These occur with different styles across the two block boundaries between North Kun Lun, Bayan Har and Qang Tang, as shown also by the changes resolved in the internal architecture and layer velocities in the crust. Clear S-waves are observed: together with P-waves they bring rare constraints on the composition of crustal units, which reveals an abnormally felsic average composition for the whole crust and its lower half along the whole length of the transect. Across the North Kun Lun–Qaidam block, variations of crustal thickness are detected, with Moho depth between 55 and 65 km, and an inverse correlation with basement topography. In the north of the Bayan Har block, a strong heterogeneity in the middle of the 70 km thick crust is shown. As suggested from synthetic seismograms modelling, it may result from thin layer inclusion marking the northward tectonic superposition of the Bayan Har crust on the North Kun Lun crust. As imaged by a fan profile, the corresponding upper part could have been transported northwards to thicken also the upper crust of the present North Kun Lun block. In the north of Qang Tang, a model is obtained with a 75-km thick crust and a lower half of the crust with average velocities characteristic of felsic composition. From Bayan Har to Qang Tang, variations of deep architecture are documented across the Jinsha suture and Xianshuihe fault from recording in-line and broadside to several shotpoints. Together with the felsic composition of the lower part of the crust, a Moho offset suggests the imbrication of the Bayan Har crust in the Qang Tang lithosphere between a south-dipping Moho above and a north-dipping Moho below. A model of indentation of the Qang Tang by an originally thinner Bayan Har crust and lithosphere, with part of the Qang Tang brought to greater depth would also be consistent also with the Moho topography across the transition from the Qang Tang to Bayan Har, as imaged by fan profile.