关键词: 金沙江断裂带, 晚第四纪活动, 大型滑坡, 特殊构造部位, 关系

Abstract:

The relationship between large-scale landslides and active faults has attracted much attention. From the point of view of active tectonics and disaster geology, the late Quaternary activity of the Jinsha River fault zone is investigated and studied, and the relationship between large-scale landslides and activity of the Jinsha River fault zone is emphatically analyzed. The Jinsha River fault zone was formed during the closure of the Paleotethys Ocean. According to the distribution of the 5km-wide ophiolitic melange zone, the ultramafic rock zone, and the local migmatization and progressive metamorphism around the Variscan intermediate acid intrusive rock mass distributed along the fault, it is inferred that the fault zone was once a strongly active superlithospheric fault zone with obvious compressive properties. The Jinsha River fault zone is a large-scale, long-term active suture structure, with many branches, forming a 50km wide structural fracture zone. Affected by the eastward compression of the Tibet Plateau, it has changed into a strike-slip fault zone characterized by dextral shear since Pliocene. In the study area, the fault landforms are clear along the Zengdatong, Xulong, Nizhong, Lifu-riyu, Langzhong and Guxue faults, which are mainly manifested as straight fault trough, linear ridge, fault scarp, and directional aligned fault facets. Results of field geological and geomorphological investigation and chronology show that the late Pleistocene and Holocene deposits are faulted, indicating the faults are active during the late Quaternary and dominated by dextral strike-slip with an average horizontal slip rate of 3.5~4.3mm/a in Holocene. The study area is located in the middle and north of the world-famous Jinsha River suture of the north-south structural belt in Sichuan, Yunnan and Tibet, and the geological structural conditions are very complex. The main structural line is distributed in NS direction, interwoven with NE and NW faults and fold axes in network shape, and the structure is complex. Strong neotectonic movement, huge topographic elevation difference, steep mountains, dry-hot valleys microclimate and other factors have caused serious internal dynamic geological disasters on both banks of Jinsha River. The landslide in the area has the characteristics of high frequency, large scale and serious damage. There are 23 large-scale and super large-scale landslides in the main stream and its tributaries of Jinsha River within the 38km-long section from Narong to Rongxue. Most of them are super large-scale landslides with a volume of more than 10 million cubic meters, even have a volume of more than 100 million cubic meters. Most of the landslides are located within 1km on both sides of faults, and many of them are developed on the fault zone. The occurrence of these large-scale landslides is closely related to the long-term activity, evolution history and complex structure of Jinsha River fault zone along the river, as a result, the rock mass structure gets fragmented and the continuous tectonic activity becomes the main cause of landslides. Active faulting is the fundamental controlling factor for the occurrence of large landslides along the river, especially for large landslides, and is an important internal dynamic condition for the formation of landslides. Further analysis of the fault structure shows that landslide is closely related to the movement evolution history of Jinsha River fault zone. Special structural combination parts(mechanical mechanism)such as closely adjacent faults, acute angle area of fault intersection, right turning parts of the faults and the intersection area between the main faults and the transverse faults are the key sites where the tectonic stress is easy to concentrate, thus conducive to generating large-scale landslides. Many large landslides occur in these structural parts. The controlling effect of active faults on landslides is not only embodied in the process of large earthquakes, but also can lead to the intensive occurrence of large and super large landslides in a natural state(non seismic action). This research has positive scientific significance for understanding the formation mechanism and development law of landslides on both sides of Jinsha River, and for understanding the relationship between fault activities and large landslides.

Key words: Jinsha River fault zone, late Quaternary activity, large-scale landslides, special structural position, relationship