中亚造山带东段深地震反射剖面大炮揭露下地壳与Moho结构——数据处理与初步解释

深地震反射大炮数据能够准确地获得下地壳和Moho的精细结构及其横向变化信息，揭露岩石圈尺度的构造样式与深部过程。中亚造山带东段位于古亚洲洋、蒙古—鄂霍茨克洋和古太平洋三大构造域的叠合区域，其岩石圈结构记录了大洋，特别是古亚洲洋消亡方式和大陆增生的深部过程。本文选用横过中亚造山带东段（奈曼旗—东乌珠穆沁旗，长约400 km）深地震反射剖面中的24个大炮数据和2个中炮数据，通过数据处理获得了近垂直反射的大炮单次剖面，揭露出中亚造山带东段下地壳及Moho的精细结构，刻画出古亚洲洋消亡极性与中亚造山带增生造山的深部过程：西拉木伦缝合带与贺根山缝合带构成古亚洲洋消亡的双缝合带，西拉木伦缝合带下方古亚洲洋板块以向南消亡为主，贺根山缝合带下方古亚洲洋板块以向北消亡为主，后者规模大于前者。在两个缝合带之间下地壳呈现出几个大规模的块状弧状反射体，推测是大洋中的残余微地块，在古亚洲洋消亡过程中拼接在一起，成为中亚造山带增生造山的一部分，并遭受了碰撞挤压和后造山伸展作用。Moho位于双程走时12 s附近（厚度约36 km），近于水平展布，沿整条剖面起伏不大。平缓的Moho成因与造山后的地壳伸展作用相关。

Lower Crust and Moho Structure of the Eastern Segment of the Centeral Asian Orogenic Belt Revealed by Large Dynamite Shots of Deep Seismic Reflection Profile:Data Processing and Preliminary Interpretation

By using the large dynamite shots data of deep seismic reflection, the key information of the structure details of the lower crust and Moho as well as their lateral variations can be obtained accurately, and the tectonic pattern and deep process of the lithospheric scale can be revealed. The eastern segment of the Central Asian orogenic belt (CAOB) is in the superimposed area of the three major tectonic domains, the Paleo-Asian Ocean, the Mongolian-Okhostsk Ocean and the Paleo-Pacific Ocean. The demise process of the ocean was recorded by its lithospheric structure, especially the demise of the Paleo-Asian Ocean and the deep process of continental accretion. In this paper, 24 large dynamite shots data and two medium shots data from the deep seismic reflection profile traversing the eastern segment of the CAOB (from East Ujimqin Banner to Naiman Banner, about 400 km long) are selected for data processing, and one large dynamite shots single profile of near-vertical reflection is obtained. The fine structure of the lower crust and Moho discontinuity beneath the eastern segment of the CAOB are revealed, and the polarity of the demise of the Paleo-Asian Ocean and the deep accretionary orogeny processing of the CAOB are described as follows: The Xar-Moron suture and the Hegenshan suture constitute double sutures related to the demise of the Paleo-Asian Ocean: The Paleo-Asian Ocean plate below the Xar-Moron suture may be primarily subducted southward; While the Paleo-Asian Ocean plate below the Hegenshan suture may be primarily subducted northward, and the latter is larger than the former in scale. Between the two sutures, several large-scale arc-shaped reflections are presumed to be residual micro-blocks in the ocean. They were spliced together during the demise of the Paleo-Asian Ocean, after collision, compression, and post-orogenic extension. A near-horizontal Moho structure is located at around TWT 12 s (about 36 km thick), which is relatively flat along the profile. The flat Moho should be related to the post-orogenic extension of the crust.