青藏高原北缘基底结构的有限差分研究

Study on the basement structure at the northern margin of Tibetan plateau by finite fifference

拜城-大柴旦综合地球物理剖面横跨了塔里木盆地、阿尔金造山带和柴达木盆地.沿剖面进行了10次各2吨级TNT炸药的人工地震探测工作.本文利用沿剖面的Pg震相,使用有限差分方法对塔里木盆地、阿尔金造山带和柴达木盆地的基底顶界面埋深及盖层的速度结构进行了反演,结果表明,不同的地质构造单元具有不同的基底结构形态与速度分布特点.塔里木盆地的基底及盖层速度分布相对平稳,表现出整体变形特征,但在库车与轮台之间,盆地的基底埋深及速度分布发生了明显的变化,深度差约2 km,速度差高达0.5 km/s.这种明显的、系统的速度差异,加之其它地质学与深部地球物理学证据表明,塔里木盆地的基底可能由构造特点不同的东西两个部分构成;阿尔金造山带的基底埋深与盖层速度分布变化较大,与造山带的强烈构造变形相联系;在阿尔金造山带与塔里木盆地和柴达木盆地的接触部位基底及盖层介质均表现为高速异常,可能与深部高密度物质沿断裂向地壳内部迁移有关;柴达木盆地的基底与盖层呈"U"形分布,表现出强烈的内部变形特征.

The comprehensive geophysical profile from Baicheng to Da Qaidam runs through the Tarim Basin.the Altyn Tagh Range and the Qaidam Basin. Ten chemical explosions with 2 ton TNT and receptions were carried out along the profile. Making use of Pg phases and finite difference method, the inversion on the structure of the basement and deposit cover of the Tarim Basin.the Altyn Tagh Range and the Qaidam Basin was conducted. The results demonstrate that different tectonic unit has different velocity distribution and structural character： The velocity distribution of the basement and deposit cover of the Tarim Basin is relatively balanced, showing an integrated deformation style of the basin. However, an obvious change of the basement and the deposited cover occurred in between Kuqa and Luntai, with a depth change of 2 km and velocity contrast of 0.5km/s. This obvious and systemic change in depth and velocity indicates that the basement of the Tarim Basin may be divided into two partsthe eastern part and the western one, combined with other geological and geophysical evidence. The velocity distribution of the basement and deposited cover of the Altyn Tagh Range appears as a biggish undulation, which may be related to strong tectonic deformation of the orogenic belt. Two high velocity zones were found at the boundaries between the Altun Tagh Range and the two basins at its both sides, indicating that the high density mass in the deep parts moves upward to the inner crust along the faults. The basement of the Qaidam Basin looks like a fovea, which has a character of intensive deformation.