摘要
大型克拉通盆地地壳上地幔组构有什么特征?其内部结构有何变化?这是目前备受关注的科学问题之一。在新世纪体波地震层析成像的研究进入区域地壳上地幔探测的视野,这个问题可通过体波地震层析成像来研究。文中结合塔里木盆地内的宽频地震记录以及新疆地震台网、中国数字地震台网资料对塔里木地区进行了同台同源的P波和S波地震层析成像,重点研究区域分辨率横向达到0.5°×0.5°,纵向达到10km间隔。通过体波到时地震层析成像反演,得到了研究区域精细地壳P波和S波速度结构。根据P波和S波速度扰动和泊松比三维图像,分析了塔里木盆地内部岩石圈波速和泊松比内部结构的信息,通过上中地壳的地震层析成像,地壳波速与泊松比结构反映了满加尔的基底、流体活动性和地温结构利于油气的成熟和保存。一般情况下莫霍面上下方波速及泊松比异常分布模式有明显区别,但塔里木盆地中央顺托果勒呈现穿透莫霍面的异常模式,解释为二叠纪岩石圈火山作用留下的"指纹"。这些信息对油气远景区定位有一定意义。
What kind of lithospheric characteristics have been developed beneath large cratonic basins?What difference in the basin structures showed during their development?These issues received much concern in recent years.Seismic body wave tomography has been a powerful tool to study the crust and upper mantle structures and has gained world-wide acknowledgment in the 21century.So the seismic body wave tomography can be applied to the investigation of these problems.In this paper,3Dhigh-resolution P-and S-wave velocity structures of the crust beneath Tarim Basin are investigated with body wave tomography by using arrival time data from same source-receiver pairs.The resolution of P-and S-wave velocity models reaches 0.5°×0.5°laterally and 10km vertically,tested by some different grid steps.We analyze the obtained 3Dimages of the Pand S-wave velocity perturbation and Poisson's ratio,interpret the crustal structures and compare differences between internal structure units within Tarim Basin.The results indicate that there are three areas that are good for oil/gas accumulation and preservation.These three areas are as follows:(1)Round Mangar depression;(2)the west part of Bachu uplift and Yecheng depression;(3)Tangutsbas and the east section of Maigait Slope.The crustal seismic anomaly distribution patterns are usually different from that beneath the Moho.But this crustal pattern at Shuntuoguole area in central Tarim Basin seems penetrating through the Moho.This kind of lithospheric structure must be distinct from general situation,being interpreted as"fingerprint"in the lithosphere,which was left by volcanism in the Permian.In conclusion,the homographic results have certain significance in oil and gas exploration.