青藏高原南羌塘盆地多玛地区 晚新生代伸展构造特征

晚新生代以来青藏高原南羌塘盆地内发育近南北走向和近东西走向的两组伸展构造。南羌塘盆地多玛地区的遥感影像分析及野外实地研究表明，沿两组断裂均可见线性分布的断层三角面、断层陡坎、断塞塘、热泉和泉华等构造地貌特征，表明断裂的伸展特性；同时，南北走向的断裂错断山脊、中生代地层和研究区内近东西走向的伸展构造，断层错距从几十米到上千米不等。近南北走向的断裂由南部的两条主干断裂向北呈马尾状散开，并在中央隆起带南坡逐渐消失，近东西走向伸展构造发育在近南北走向断裂的北部，不论断层规模还是断层活动性均表明近南北走向断裂为研究区内主控构造单元。光释光年龄表明近东西走向断裂在全新世仍处在活动状态。研究区内两组伸展构造的交切关系表明近东西走向的伸展构造为近南北走向构造的伴生构造或转换构造，两组伸展构造的发育表明高原腹地处于伸展垮塌状态。

Late Cenozoic extension structure in Duoma area,South Qiangtang Basin of central Tibet

Two groups of extensional structures, the N-S-trending and the E-W-trending extension structure, developed since Late Cenozoic in central Tibetan Plateau. According to remote sensing image analysis and field work in Duoma area of the South Qiangtang Basin, geomorphology is characterized by the linear distribution of fault facets, fault scarp, sag pond, thermal spring and travertine, which indicates the extension characteristics of those structures. The N-S-trending extension structures cut the ridge, Mesozoic strata and the E-W-trending extension structures with offset ranging from tens to thousands of meters. The N-S-trending strike fault spreads northward as horsetail structure from two main faults in the south and gradually disappears in the south of the central uplift belt in the Qiangtang terrane. The W-E-trending extension structure is developed in the north segments of the N-S-trending strike fault. Both fault scale and fault activity indicate that the N-S-trending extension structure is the domination tectonic unit in this area. The east-west fault is still active in Holocene according to the Optically Stimulated Luminescence（OSL）ages. The intersecting relationship between the two groups of extensional structures indicates that the E-W-trending extensional structure is the associated structure or transitional structure of the N-S-trending extensional structure. The development of the extensional structures in the two groups indicates that the central Tibet Plateau is in the state of extension collapse.