【摘要】 利用文登—阿拉善左旗长观测距地震宽角反射/折射剖面东段资料,辩识出4组地壳震相和3组地幔盖层震相.采用二维射线追踪走时反演和正演拟合交替计算方法,得到了包括鲁东隆起和华北裂陷盆地在内的地壳和地幔盖层二维速度结构.研究结果表明:华北裂陷盆地基底深达6km以上,研究区壳内界面C1埋深约15km,C2界面深约25km,Moho面平均埋深约35km.上地壳速度6.0~6.1km·s-1,且横向变化较大;中地壳速度相对均匀约为6.2~6.4km·s-1;下地壳速度为6.5~7.0km·s-1,速度梯度较大.地壳平均速度与隆起和坳陷构造相关.研究区岩石圈底界面一般为75~80km,西端接近太行隆起构造时深至90km左右,向西呈明显加深趋势,地壳厚度呈现相同的增厚特征.地幔盖层上部速度8.0~8.2km·s-1,具明显正梯度特征.岩石圈平均速度在郯庐断裂带附近显著偏低.PmP和PLP震相存在不同程度的复杂性,意味着在本地区Moho界面和岩石圈界面有较为复杂的结构,可能具有一定厚度或过渡带性质.结合其他研究结果认为,地幔盖层和下地壳速度梯度、界面性质差异与华北克拉通破坏相关,意味着破坏是一个渐变、缓慢和不均匀的过程.郯庐断裂带附近的低速应是其为软弱带的证据.更多还原

【Abstract】 The destruction of North China Craton(NCC)plays an important role in understanding the continent′s formation and evolution.Long-range deep seismic sounding profile is a valid method in studying on NCC′s tectonic evolution since it can give more accurate information of the lithosphere′structure and thickness.In fact,most research results of structure deeper than crust are based on earthquake data due to economic and technological factors and hardly on artificial sources data.The structure reconstruction of crust and lower lithosphere beneath east section of Wendeng-Alxa Zuoqi has been performed from a long-range seismic wideangle-reflection/refraction data in order to provide seismic evidence for the destruction of NCC.We identified several crust and lower lithosphere phases on the long-range wide-angle-reflection/refraction seismic record sections.Then the velocity structure of crust and lower lithosphere has been reconstructed by use of the method of two-dimensional inversion and forward calculation of travel times alternatively.The destruction mechanism and process of NCC have been discussed according to the structure of crust and lower lithosphere obtained in this work taking into account of the previous research results.Four seismic phases are identified and defined as follows:the first arrive,Pg,is a diving wave penetrating into the sedimentary or the crystalline upper crust,the phases of P1 P and PcP are reflections from intracrustal layers,PmP is a strong wide angle reflection from the Moho or refraction from the lower crust.The other 3phases beneath the Moho are identified,Pn,PL1,PLP,of which PL1 and PLP are refraction and reflection phases from lower lithosphere.The results show the basement depth of North China Rift Basin is 6km,the depths of C1 and C2interfaces within the crust are~15km and~25km respectively and the average depth of Moho is~35km.The upper crustal velocity is 6.0~6.1km·s-1 characterized by larger lateral variations,the middle crust is relatively uniform with the velocity 6.2~6.4km·s-1 and the velocity of lower crust is 6.5~7.0km·s-1 with a vertical larger velocity gradient.The average crust velocity is associated with the uplift or depression tectonics.The lithosphere bottom is generally 75~80km in depth and it increases to~90km at the western end near to Taihang uplift region,and the crust also thickens westwards.The velocity of upper part of lower lithosphere is8.0~8.2km·s-1 showing distinct positive gradient feature while lithosphere average velocity around Tan-Lu fault zone is observably lower.The different complexity of PmP and PLP phase means a more complex structure of Moho and lithosphere bottom which probably has a certain thickness or behave as a transitional zone.The thickness of lithosphere is 75~80km in the research area which is consistent with the results from receiver function.The results of the 2Dvelocity structure model,relatively lower avereage velocity of lithosphere around Tan-Lu fault zone and complicated transition zone structures between crust and mantle and between lithosphere and asthenosphere obtained by this work,support the conclusion that the process of destruction of NCC is complicated and gradual,and a tectonic weak belt of lithospheres′mantle occurs near the Tan-Lu fault zone.更多还原