【摘要】 利用横贯柴达木盆地南北的格尔木—花海子剖面岩石圈二维P波速度结构以及地震波速度与介质密度之间的关系,建立了该剖面岩石圈二维密度结构与二维磁化强度的初始模型。依据重磁同源原理,在柴达木盆地重、磁异常的二重约束下完成了重磁联合反演,获得了该剖面岩石圈二维密度结构与二维磁化强度分布。结果表明:柴达木盆地地壳厚度沿测线变化较大,平均厚度约60km。在柴达木盆地南缘地壳厚约50km,达布逊湖附近地壳最厚为63km左右,大柴旦附近地壳较薄,为50km左右。柴达木盆地的地壳纵向上可分为三层,即上地壳、中地壳与下地壳。位于盆地中部的中、下地壳分别发育大范围的壳内低密度体,并处于上地幔隆起的背景之上;横向上可将盆地分成南北两个部分,分界在达布逊湖附近。整个剖面结晶基底埋深变化也很大,在达布逊湖附近为12km,在昆仑山北缘基底几乎出露地表。结晶基底的展布形态与地壳底界,即莫霍面呈近似镜像对称。综合研究认为,柴达木盆地的岩石圈结构存在着明显的南北差异,其分界在达布逊湖的北面。在盆地南部,岩石圈介质横向变化较小,各层介质分布正常;在盆地的北侧,岩石圈结构特别在中、下地壳和上地幔顶部横向上发生了变化。壳内低密度体的存在意味着柴达木盆地具有较热的岩石圈和上地幔,加之基底界面与莫霍面的镜像对称分布,形成与准噶尔盆地和塔里木盆地的构造差异。多种地球物理参数所揭示的地壳上地幔结构及其横向变化特点为柴达木盆地构造演化及青藏高原北部边界的地球动力学研究提供了岩石圈尺度的地球物理证据。更多还原

【Abstract】 From 2-D P-wave velocity structure along a profile from Golmud to Huahaizi in the Qaidam basin and the relationship between seismic wave velocity and media density,we have constructed the initial 2-D model of lithospheric density and magnetic intensity along the profile.Based on gravity and magnetic fields caused by the same source,we have conducted a joint gravity-magnetic inversion in the basin.The inversion shows that the crustal thickness in this basin varies greatly along the profile.The average thickness is about 60 km.The thickness near the southern edge of the basin is about 50 km.The thickest crust of about 63 km lies near Dabsan lake and the thinner one near Da Qaidam is about 50 km.The crust in the Qaidam basin can be divided vertically into three layers:the upper,the middle and the lower layer.Some low-density bodies widely exist in the middle crust of the center of the basin,and in the upper crust above the uplifted portion of the upper mantle.The basin can be divided into two parts laterally by a boundary near Dabsan lake.The depth to crystalline basement varies greatly along the profile.It is about 12 km near Dabsan lake,and is nearly exposed at the northern edge of the Kunlun mountains.The distribution of the crystalline basement has a symmetrical relation with the Moho.Comprehensive studies show that there exist obvious distinctions in lithospheric structure between the south and the north Qaidam basin with a boundary in the north of Dabsan lake.In the southern part of the basin,the character of the lithosphere varies little laterally,with normal distributions in each layer.In the northern part of the basin,the lithospheric structure,especially that of the middle crust,lower crust and uppermost mantle,varies laterally.The low density bodies in the crust suggest that a hotter lithosphere and uppermost mantle exists in the Qaidam basin;moreover,there is a symmetric distribution of the crystalline basement to the Moho in this basin;and these features are different from those of the Junggar basin and the Tarim basin.The crust and uppermost mantle structure and its characteristics of lateral variation revealed by multi-geophysical parameters provide lithospheric scale evidence for the tectonic evolution of the Qaidam basin and the geodynamics of the northern edge of the Tibetan plateau.更多还原