阿尼玛卿缝合带东段上地壳结构——马尔康—碌曲—古浪深地震测深剖面结果

UPPER CRUST STRUCTURE OF EASTERN A’NYMAQN SUTURE ZONE:RESULTS OF BARKAM-LUQU-GULANG DEEP SEISMIC SOUNDING PROFILE

位于青藏高原东北缘川北甘南地区的马尔康—碌曲—古浪深地震测深剖面穿越阿尼玛卿缝合带东段,利用该剖面获得的Pg,Sg初至折射波资料,采用有限差分成像、射线追踪反演、时间项反演和走时曲线分析等方法,对阿尼玛卿缝合带东段及其两侧的上地壳结构进行了分析.结果表明,研究区基底变化较大.由南向北,基底在若尔盖盆地呈稳定的上隆状态,在阿尼玛卿缝合带内强烈下陷,在缝合带北侧一定范围内隆升之后,向北呈下陷趋势.阿尼玛卿缝合带相对两侧整体表现为南倾的低速带结构,且内部速度存在非均匀性.库赛湖—玛沁断裂、武都—迭部断裂和舟曲—两当断裂均表现为不同规模的低速带.库赛湖-玛沁断裂和舟曲—两当断裂位置处基底界面埋深有明显变化,是区隔阿尼玛卿缝合带南北两侧的主要断裂.武都—迭部断裂发生在基底界面深度变化带上,它与舟曲—两当断裂可能具有同一深部构造背景.阿尼玛卿缝合带所呈现的强烈下陷的基底低速结构和非均匀性体现了上地壳受挤压的破碎结构特征.

Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A＇ nye^^maqe^^n suture zone. The upper crust structures around eastern A＇nye^^maqe^^n suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoige^^ basin and depressed in eastern A＇ nye^^maqe^^n suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A＇nye^^maqe^^n suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined toward the south. Hoh Sai Hu-Maqe^^n fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqe^^n fault and Zhou- qu-Liangdang fault, which are main tectonic boundaries of A＇ nye^^maqe^^n suture zone. Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A＇nye^^maqe^^n suture zone implies crushed zone features under pinching action.