【摘要】 利用中法1995年布设在跨过阿尔金断裂剖面上的18个流动三分量地震台站记录到的近5个月的天然地震记录,经筛选得到533个高质量接收函数。通过速度分析和接收函数成像处理,得到了阿尔金断裂附近地壳结构的清晰图像。塔里木盆地的Moho界面非常清楚,近水平地位于~44km深度上。该界面以低缓的角度一直向南延伸到了阿尔金断裂附近的~70km的深度。阿尔金断裂以南柴达木盆地下面的Moho界面也十分清楚,近水平地位于~55km的深度上,在阿尔金断裂附近存在向上挠曲,并抬升到了~45km的深度上。在阿尔金断裂下方,Moho界面存在~15km的错断。塔里木盆地Moho之下还存在另一个震相,我们解释为沉积层多次波与可能来自Hales间断面转换波的复合震相。接收函数成像结果表明阿尔金断裂是一个超壳的岩石圈断裂,具有比较直立的产状和很狭窄的剪切变形带。根据这些结果,我们推测塔里木的下地壳可能要比柴达木的下地壳更硬,柴达木地壳增厚的原因可以部分归结于它有一个相对弱的下地壳,青藏高原隆升没有扩展到塔里木盆地是因为塔里木盆地具有更刚性的下地壳和岩石圈地幔。高原北部地壳变形应该是所谓青藏高原隆升的“硬”变形模式(Tapponnieretal.,2001)和“软”变形模式(EnglandandHouseman,1989;ClarkandRoyden,2000)共同作用的结果。更多还原

【Abstract】 In the framework of a Sino-French cooperative project 18 three-component portable seismic stations were deployed across the Altyn Tagh fault (ATF) for about five months. From the data recorded on this array, 533 receiver functions with sufficient quality are selected and used in this study. A cross-section about the detailed crustal structures across ATF is then obtained after velocity analysis, common conversion point migration and stacking processes. The Moho discontinuity on the Tarim side is distinctly imaged sub-horizontally at depths of ～44 km. This discontinuity underthrusts gently and smoothly under the Altyn Tagh to a depth of ～70 km beneath ATF. The Moho discontinuity south of ATF is also obvious, and distributed sub-horizontally around ～55 km depth. But, it is heaved up, or “plowed up”, by the Tarim lower crust to a depth of ～45 km near ATF. A fault offset of ～15 km in Moho is seen approximately under the surface trace of ATF. There is an another phase observed ～20 km below the Moho in the Tarim basin, which is interpreted to be the compound energies from the multiple converted phases in the sedimentary layer and the directly converted phases of the Hales discontinuity. Our results indicate that ATF is a lithospheric fault, which extends sub-vertically and characterised by a narrow shear zone. Based on these results, we conclude that the lower crust beneath the Tarim basin is more “hard” than that beneath the Qaidam basin. The thickening of Qaidam crust may be partly ascribed to its more “soft” lower crust. The Tibetan plateau can not grow into the Tarim basin is probably simply because the later has more “hard” lower crust and lithospheric mantle. Our results imply that the mechanism of crustal deformation in the northern-most plateau might have some major features outlined in the “hard Tibet” paradigm (Tapponnier et al., 2001) and but also have some other major characters described in the “soft Tibet” paradigm (England and Houseman, 1989; Clark and Royden, 2000).更多还原