| 二维初至波层析成像揭示的北祁连—阿拉善南缘浅层地壳结构 |
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| 引用本文：吴国炜,熊小松,高锐,陈宣华,李英康,叶卓,王冠,吴鸿梅.2022.二维初至波层析成像揭示的北祁连—阿拉善南缘浅层地壳结构[J].地球学报,43(6):843-857. |
| DOI：10.3975/cagsb.2022.062501 |
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| 基金项目:国家自然科学基金(编号: 41774114; 41590863; 41574093);中国地质调查局项目(编号: DD20190011; DD20179342; DD20160083);国家重点研发计划课题(编号: 2016YFC0600302) |
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| 中文摘要:北祁连造山带—阿拉善南缘位于青藏高原东北缘及其以北地区, 其地壳结构记录了早古生代以来祁连山、河西走廊盆地、合黎山及相邻盆地之间的盆山演化历史及耦合关系, 对其地壳浅层速度结构的探测有助于揭示该区浅层地壳结构及构造变形的演化历史。本文利用北祁连—阿拉善南缘225 km长的深反射地震剖面的初至波(Pg震相)数据, 通过层析成像反演方法, 获得了沿线2 km以浅的上地壳P波速度结构。其主要特征为: 酒东盆地的沉积盖层厚度最大可达2 km, 盆地深度的南北差异可能与阿拉善地块与祁连造山带间的挤压作用相关; 民乐盆地的平均深度为1.5 km, 该盆地内的速度等值线弯曲形态反映了盆地在新生代之后不同的抬升和剥蚀速率; 银额盆地的沉积厚度至少在1.5 km左右, 且盆地内沉积地层产状较为平缓; 榆木山构造带南北两侧的酒东盆地与民乐盆地虽然地表高程相差近1 km, 但具有近乎相同的速度结构和沉积厚度, 推断榆木山构造带的隆升与其南北两侧的两个断层背冲作用有关; 此外, 反演得到的P波速度结构揭示了沿线发育的多条断裂和块体边界位置, 为讨论青藏高原东北缘向北扩展与阿拉善地块挤压作用提供了新的证据。 |
| 中文关键词:北祁连造山带 阿拉善地块 层析成像 上地壳速度结构 |
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| Shallow Crustal Velocity Structure of the North Qilian–Southern Alxa Block Revealed by 2D First-arrival Seismic Tomography |
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| Abstract:The North Qilian orogenic belt–southern Alxa Block is located in the northern region of the Qinghai-Tibet Plateau on its northeastern margin. The crustal structure of the belt records the evolution and coupling relationship, since the Early Paleozoic, between the Qilian Mountains, Hexi Corridor Basins, Heli Mountains, and adjacent basins. Detection of the shallow crustal velocity structure will help to reveal the evolutionary history of the crustal structure and the tectonic deformation in this area. In this study, a shallow upper crust P-wave velocity structure from 2 km underground was obtained by using the first-break (Pg) seismic phase data of a deep reflection seismic profile (225 km long) between the North Qilian orogenic belt to southern Alxa Block, using tomographic inversion. The main characteristics were as follows: the thickness of sedimentary cover in Jiudong Basin is up to 2 km, and the difference in basin depth between north and south may be related to the compression between the Alxa block and Qilian orogenic belt; the average depth of Minle Basin is 1.5 km, and the curves of velocity isolines in the basin reflect different uplifting and denudation rates since the Cenozoic; the sedimentary thickness of Yine Basin is at least 1.5 km, and the occurrence of sedimentary strata in the basin is relatively gentle; Jiudong Basin and the Minle Basin on the north and south sides of Yumushan tectonic belt have virtually the same velocity structure and sedimentary thickness, although the surface elevation difference is nearly 1 km. It can be inferred that the uplift of the Yumushan tectonic belt is related to the backthrust of two faults on the north and south sides. In addition, the P-wave velocity structure obtained by inversion reveals the location of multiple faults and block boundaries that developed along the line, which provides a new evidence for discussing the northward expansion of the northeastern margin of the Qinghai-Tibet Plateau and the compression of the Alxa block. |
| keywords:North Qilian Orogenic Belt Alxa Block tomographic imaging upper crust velocity structure |
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