格尔木－额济纳旗地学断面的地壳结构与深部构造

THE CRUSTAL AND DEEP STRUCTURES IN GOLMUD-EJIN QI GGT

格尔木－额济纳旗地震测深剖面，横跨柴达木盆地、祁连山和北山地区．主剖面长１０５０ｋｍ，共获１４条单支波形记录剖面和２条非纵剖面．确认了Ｐｇ，Ｐｍ，Ｐ１，Ｐ２，Ｐ３，Ｐ４及Ｐｎ波组．据各记录剖面各波组的时距曲线进行了反演计算和二维正演拟合，建立了二维速度结构模型．波场特征表明，地壳层状结构明显．地壳分为３层：上地壳由５．５－６．０ｋｍ／ｓ的梯度层和６．１－６．３ｋｍ／ｓ的常速层组成，平均速度为５．８－６．１ｂｍ／ｓ，厚度为１３．５－２０ｋｍ；中地壳由５．８－５．９ｋｍ／ｓ的低速层和６．４ｋｍ／ｓ的常速层组成，平均速度为６．１－６．３ｋｍ／ｓ，厚１８ｋｍ左右；下地壳速度为６．６－７．４ｋｍ／ｓ，厚约１２－２６ｋｍ．上地幔速度为８．１－８．２ｋｍ／ｓ，局部为７．８ｋｍ／ｓ．地壳结构在横向上变化较大．将全线划分为三个不同的构造单元：１．柴达木地块：地壳厚度为５０－５３ｋｍ，中部薄、边缘厚．地壳平均速度为６．１－６．２ｋｍ／ｓ，相对较低，中地壳有低速层，有稳定的上地幔和活动的地壳．２．祁连山构造带：地壳厚度较大，一般大于６０ｋｍ，哈拉湖地区为７０ｋｍ左右．地壳平均速度为６．３５ｋｍ／ｓ，有低速层，且厚度较大，下地壳有?

Golmud-Ejin Qi Deep Seismic Sounding(DSS) Profile crosses three regions, that is Qaidam basin, Qilian mountain and North mountain. The main profile is about 1000 km long. There are 14 pieces of single branch extended spread and 2 pieces of broadside spread.The wave groups Pg, Pm, P1, P2, P3, P4 and Pn have been identified. According to the time-distance curves for different wave group on the record sections, the inversed and 2-D direct calculation has been completed. On the basis of that, whole profile 2-D velocity structure model has been established.The layered structure is clear as shown by the wave field features. The wave group Pg and P2 are strong, P3 and P4 weaker, the Moho reflection Pm is strong again. According to these features, the crusts is divided into three layers: The upper crusts consists of two layers. One is a gradient layer in which the average velocity is from 5. 5 to 6. 0 km/s along the profile. The other is a constant velocity layer, the velocity varies from 6. 1 to 6. 3 km/s along the profile. The average velocity of upper crust is 5. 7 to 6. 1 km/s, the thickness is 13. 5 to 20 km. The middle crust also consists of two layers. One is a low-velocity layer of 5. 8 to 5. 9 km/s. The other has a constant velocity of 6. 4 km/s. The average velocity of whole middle crust is 6. 1 to 6. 3 km/s. Its thickness is 18 km. The lower crust consists of one layer with a velocity 6. 6 to 7. 4 km/s, the typical value is 6. 8 km/s. Its thickness is 12 to 26 km. The velocity of upper mantle is generally 8. 1 to 8. 2 km/s, but is 7. 8 km/s in some areas. The crust structure varies quite strongly along the profile.The whole profile is roughly divided into three different units: 1. Qaidam block: The thickness of crust is 50 to 53 km. It is thinner in the middle and thicker outwards. The average velocity of crust is 6. 15 to 6. 17 km/s, which is comparatively low. There is a lowvelocity layer in the middle crust. This unit has a steady upper mantle and active crust.2. Qilian mountain tectonic zone: The crust is generally thicker than 60 km, nearly 70 km in the Harhu area. There is a relatively thick low-velocity layer. The average velocity is 6. 35 km/s. The lower crust tends to be thicker. It has an active upper mantle and active crust. 3. North mountain tectonic zone: It features a thinner crust between 40 to 43 km.The average velocity is 6. 5 km/s. There is an inversion in velocity values in the middle crust, but it is not low enough to be called a low-velocity layer. Its value is 6. 0 to 6. 1 km/s. This unit has an active upper mantle and a steady crust.The crust structure of each unit has little relation with the crust movement before Mesozoic Era, but is closely related with geomorphologic unit and the feature of gravity map. For this reason, it can be known that they are a result of Himalaya movement.