【摘要】 汉中盆地位于秦岭造山带与上扬子板块的交接之处，西侧紧邻松潘—甘孜地块，是研究新生代以来秦岭造山带隆升、青藏高原东北缘向外扩展的理想区域.本文利用58个宽频地震台站在2014年1月至3月的连续波形记录，对背景噪声做互相关并采用时间尺度的相位加权叠加方法增强信噪比，进而提取出2～30 s内的基阶瑞利面波相速度频散曲线.通过面波走时直接反演方法获得汉中盆地及邻区地壳(2～30 km)的高分辨率三维S波速度结构.研究结果显示:(1)汉中盆地浅部速度存在较明显的东西差异，西侧低速区域比东侧更深，反映了盆地西部断拗陷、东部浅断陷的构造特点.盆地上地壳速度层向南倾斜，这可能受到了北侧秦岭山脉在新生代快速隆升的影响.此外，印支期到燕山期的沉积间断可能导致了盆地中、上地壳出现S波速度跃升的情况.(2)秦岭造山带在中、上地壳呈现出特殊的反地壳速度结构特征.其中，上地壳的显著高速体推测与古生代板块俯冲碰撞导致高压超高压变质岩的产生以及后续多期次的折返有关.秦岭中地壳的低速异常主要反映了长英质的地壳组分，这可能是由于中生代的拆沉作用造成了下地壳基性岩层的缺失.(3)研究区域中、下地壳未出现明显低速异常，意味着新生代青藏高原东缘的中、下地壳流可能未向东流入秦岭及汉中盆地.更多还原

【Abstract】 The Hanzhong basin, located at the junction of the Qinling orogenic belt and the Upper Yangtze plate,is adjacent to the Songpan-Garzêblock to the west.It is an ideal region for studying the uplift of the Qinling orogenic belt and the outward expansion of the northeastern margin of the Tibetan Plateau since the Cenozoic.In this study,continuous waveform records from 58 broadband seismic stations were used from January to March 2014.Cross-correlation of ambient noise was performed,and the time-scale phase-weighted stacking method was employed to enhance the signal-to-noise ratio.As a result,phase velocity dispersion curves of the fundamental Rayleigh waves in the range of 2～30 s were extracted.Using the direct inversion method of surface wave travel times,high-resolution 3-D S-wave velocity structure in the crust (2～30 km) of the Hanzhong basin and adjacent areas was obtained.The results reveal that:(1) There is an obvious east-west difference in the velocity of the shallow basin that the low-velocity area in the west is deeper than that in the east,reflecting the tectonic characteristics of the western fault depression and the eastern shallow fault depression in the Hanzhong basin.The upper crustal velocity layer of the basin displays southward tilting,likely influenced by the rapid uplift of the Qinling Mountains in the north during the Cenozoic.Furthermore,sedimentary discontinuities from the Indosinian to the Yanshanian periods caused abrupt increases in S-wave velocity within the middle-upper crust of the basin.(2) The Qinling orogenic belt exhibits special inverted velocity structure characteristics in the middle-upper crust.The significant high-velocity body in the upper crust is inferred to be related to the generation of high pressure-ultrahigh pressure metamorphic rocks resulting from Paleozoic plate subduction and collision,as well as subsequent multiple stages of exhumation.The low-velocity anomaly in the middle crust of the Qinling,primarily reflecting felsic crustal components,may be due to the removal of lower mafic crust by delamination during the Mesozoic.(3) In the study area,there is no notable low-velocity anomaly in the middle-lower crust,suggesting that the middle-lower crustal flow on the eastern margin of the Tibetan Plateau during the Cenozoic may not flow eastward into Qinling and Hanzhong basin.更多还原