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摘要: 鄂尔多斯块体及周边区域的深部构造研究对于了解华北克拉通与其周边地带形成、发展和克拉通破坏具有怎样的壳、幔结构和深层动力学过程具有重要的意义.本文利用北京大学和中国地震局在华北克拉通西部地区布设的共32台宽频带地震仪记录的远震体波资料,组成一条近南北向的观测剖面,由北至南依次穿过阴山造山带、河套盆地、鄂尔多斯块体、渭河盆地、秦岭造山带和大巴山系.计算各台站的P波接收函数,利用倾斜叠加(H-κ)方法得到了研究区域地壳厚度和泊松比;利用Kirchhoff偏移成像方法得到了研究区域下方Moho面的形态.研究结果表明,阴山造山带地壳厚度为42~44 km,地壳结构稳定,泊松比约为0.27,推测该区域的造山运动是深部物质上涌导致.河套盆地内Moho面抬升,可认为是岩石圈物质上涌导致.鄂尔多斯块体内平均地壳厚度41.2 km,泊松比0.27,Moho面从北至南平缓有平缓抬升的趋势,从最北端的43.5 km到最南端的39 km.鄂尔多斯块体北部在20 km深度处存在低速层,块体内部36°N~37°N区域内出现Moho面小规模下沉,这对鄂尔多斯块体地壳结构单一、完整、未遭到破坏的观点提出了挑战.渭河盆地内Moho面隆起,最浅达到30 km,推测是青藏高原地壳上地幔物质向东挤出并上涌所造成的.秦岭造山带地壳厚度约38.5 km,Moho面平稳.位于扬子板块北缘的大巴山系地壳厚度达到54.5 km,明显大于华北克拉通的地壳厚度.Abstract: The deep structure investigation in Ordos Block and surrounding regions is important to reveal the formation, evolution and destruction of North China Craton. Receiver function analysis is used to image the crustal structure along an N-S broadband seismic observation profile consisting of 32 temporary and permanent broadband seismic stations. The profile crosses the following geologic settings from north to south:Yinshan Oregon, Hetao Graben, Ordos Block, Weihe Graben, Qinling Oregon and Dabashan Oregon. Slant stack (H-κ) method is used to get the crust thickness and poison ratio. Also Kirchhoff migration method is used to image the Moho discontinuity in the study area. The results reveal that the crust thickness in Yinshan Oregon is about 42~44 km and the poison ratio is about 0.27. The stable crustal structure indicates that the orogeny in Yinshan is driven by the upwelling of the material from the deep. The uplift of Moho in Hetao Graben reflects the upwelling of the lithospheric material. In Ordos Block, the average crust thickness is 41.2 km and the poison ratio 0.27. The Moho slightly goes up from 43.5 km in north to 39.0 km in south. In the north part of Ordos Block there appears a low velocity layer in 20 km depth. Besides, there is an abrupt small-scale subsidence of Moho 36°N~37°N in the block. These two results challenge the common view that the crust structure in Ordos Block is simple and unbroken. In Weihe Graben the Moho bulge up to the depth of 30 km, which is supposed to be the result of the extrusion and upwelling of the Tibetan Plateau. In Qinling Oregon the average crust thickness is 38.5 km and the Moho varies slightly. In the Dabashan Oregon, the north part of Yangtze Plate, crust thickness attains to 54.5 km which is distinctly larger than the North China Craton.
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Key words:
- receiver function /
- slant stack(H-κ) /
- Kirchhoff migration /
- Ordos block /
- crust thickness /
- poison ratio
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