新疆地学断面(泉水沟-独山子)深地震测深成果综合研究

An Integrated Study of Deep Seismic Sounding Profiling along Xinjiang Global Geosciences Transect (Quanshuigou-Dushanzi)

新疆地学断面 (泉水沟 独山子 )深地震测深剖面的分段成果已经先期分别发表 ,根据已经发表的资料 ,本文着重全线震相的对比 ,并讨论地壳构造与地质演化的关系。该剖面全长约 12 0 0km ,南起西昆仑山 ,穿过塔里木盆地 ,跨越天山 ,止于准噶尔盆地南缘。该剖面共设 12个炮点 ,共用炸药 2 0t,投入地震仪 12 0台 ,共获有效三分量记录 973个。在折合时间记录截面图上识别出 6个震相 (Pg,P2 ,P3,P4,Pm,Pn) ,经走时反演和射线追踪拟合获得速度结构模型。最终的模型显示塔里木盆地主体的地壳厚度为 3 8～ 4 6km ,而且塔里木南缘的Moho界面南倾 ,与结晶基底南倾的角度大体一致。从塔中隆起至西昆仑山前 ,Moho面深度从 4 0± 2km加深到 5 7km ,但继续向南深入到西昆仑北坡之下 ,Moho产状变平 ,深度减小到 5 4km。以西昆仑北坡基底抬升、下地壳增厚和山前凹陷内存在巨厚沉积的观测事实为依据 ,推断塔里木盆地南缘地壳向西昆仑山下俯冲 ,但俯冲的距离和深度可能有限。天山地区观测到了清楚的Pn 震相 ,速度为 8.15km/s。整个天山地区Moho平均深度为 5 2km ,地壳结构复杂 ,其中地壳为 3～ 7km厚 ,速度值 5 .6km/s的低速层。中天山之下的Moho略显隆起 ,中、北天山交界处Moho明显错断。地壳内部各层厚度横向变化较大 ,具?

Some achievements in the study of the Deep Seismic Sounding profiling along Xinjiang Global Geosciences Transect (GGT) have been published in succession. This paper focuses on the comparison of the seismic phases along the whole profiling and the investigation of the relationship between crustal structure and geological evolution. The profile extends from the West Kunlun Mountains across Tarim Basin and the Tianshan Mountains, and terminates at the southern margin of Junggar basin, approximately 1 200 km long. Totally 12 shot points were designed along the profiling. During the field experiment 20 tons of explosive charges were used to generate seismic wave and 120 sets of seismographs were put into use for observation. As a result, totally 973 effective 3 component records were obtained. On the reduced travel time sections, 6 seismic phases (P g,P 2,P 3,P 4,P m,P n) were recognized. The final crustal velocity model was built by inverse calculation and ray tracing modeling. The final model indicates that the thickness of the main part of Tarim basin varies in the range of 38～46 km.The model also reveals that the Moho dips southward beneath southern Tarim basin at an angle in concordance with the angle of the crystalline basement. From central uplift of Tarim to the front of West Kunlun, the depth of the Moho increases from 40±2 km to 57 km. Further southward beneath the northern part of West Kunlun, the Moho interface suddenly becomes flat and the depth also decreases to 54 km. Based on the surveyed results that crystalline basement is uplifted, lower crust thickens beneath the northern part of West Kunlun, and huge sediments exist in the foredeep of Tarim, the authors have reached the conclusion that the crust of southern Tarim basin subducted a limited distance and depth beneath West Kunlun. In the region of Tianshan Mountains, The P n phases, with a velocity of 8.15 km/s, were recorded clearly. The Moho interface appears at an average depth of 52 km and the crust has a quite complex structure with a low velocity layer (3～7 km in thickness, 5.6 km/s in mean velocity) in the middle crust. It is also found that Moho is gently uplifted under Central Tianshan and is obviously ruptured under the boundary between Central Tianshan and North Tianshan. The thicknesses of various layers composing the crust vary remarkably in the lateral direction, and the structural characteristics suggest that the crust has been shortened as a result of the compression both from the south and from the north.