宽角反射、折射地震数据与重力数据综合解释龙门山及邻近地区地壳结构

The crustal structure of the Longmen Shan and adjacent regions： An integrated analysis of seismic profiling and gravity anomaly

青藏高原东部的隆升机制一直都是地学界的研究热点，研究学者们提出和发展了多种岩石圈变形模型，而存在多种模型的主要原因之一是对青藏高原东部地壳及岩石圈结构认识不足。本文主要针对SinoProbe-02项目横跨龙门山断裂带、全长400多公里的宽角、折射地震数据及重力数据进行联合反演和综合解释。研究结果表明，龙门山及邻近地区地壳结构可明确划分为上地壳、中地壳和下地壳。上地壳上层为沉积层，龙门山断裂带以西大部分区域被三叠纪复理岩覆盖，而在龙日坝断裂与岷江断裂之间出现了密度为2．7g／cm^3的高速异常体；向东靠近龙门山地区，沉积层厚度逐渐减薄。中地壳速度变化不均一，而且变形强烈；若尔盖盆地和龙门山断裂带下方出现明显低速带；中地壳在龙门山西侧厚度加厚，在岷江断裂下方和四川盆地靠近龙门山断裂带地区附近厚度达到最大。莫霍面整体深度从东往西增厚，最厚可达56km。本次研究得到的地壳结构和密度分布分析结果表明现有的地壳厚度和物质组成不足以支撑龙门山及邻近地区目前所达到的隆升高度，因此四川盆地刚性基底西缘因挤压作用产生的弯曲应力也是该地区抬升的重要条件之一。

Uplift mechanism of the eastern Tibetan Plateau has been the study focus among geologists, and numerous models were proposed, which mostly was owing to the incomplete understanding of the lithospheric structure beneath the eastern Tibetan Plateau. In this study, inversion, as well as integrated analysis and interpretation were carried out based on the SinoProbe-02 400 km-long wide-angle, reflection seismic line across the Longmen Shan fault zone of eastern margin of the Tibetan Plateau. The results indicate that crustal structure beneath the Longmen Shan fault zone and adjacent areas is composed of three layers, including the upper crust, middle crust and lower crust. The upper part of the upper crust is the sedimentary cover. Triassic flysch deposited in the Longmen Shan fault zone and the areas to the west. However, an anomalously high velocity body with 2.7 g/cm~ density appears in the area between the Longriba fault and the Minjiang fault. The sedimentary thickness decreases toward the east to the Longmen Shah fault zone. The middle crust is seen with relatively homogeneous velocity, but shows intense deformation. An obviously low velocity zone is present below the Ruo＇ergai Basin and the Longmen Shan fault zone. The mid-crustal thickness increases toward the western Longmen Shan fault zone and increases to the maximum beneath the Minjian fault zone and the Longmen Shan fault zones. The Moho layer deepens from east to the west and can reach to the thickness of 56 km. The obtained results regarding the distribution of crustal thickness and density indicate that current crustal thickness and composition is not enough to support current elevation of the Longmen Shan fault zone and adjacent areas. Therefore, flexure of the Sichuan rigid basement in the west from increase of the elevation. compression could also have contributed to the