Characteristics of relative tectonic activity in the Longchuan River Basin, central Yunnan: evidence from digital elevation model-based geomorphological analysis

Abstract

The Longchuan River basin lies within the China Sichuan-Yunnan rhomboid block. The NS-trending Yuanmou-Lvzhi River Fault (YLF), NW-trending Chuxiong-Nanhua Fault (CNF) and Shiyang-Huoshaotun Fault (HSF) are found within the basin. The nature of the faults is complex, and the tectonic activity distribution characteristics require further clarification. By extraction from a digital elevation model, the measured longitudinal profile and the geomorphic indices of the Longchuan River, basin showed a stream-length gradient index (SL) of 49-650, hypsometric integral (HI) of 0.27-0.58, drainage basin asymmetry factor (AF) of 3.29-27.47, basin shape index (BS) of 0.87-2.75, valley floor width-to-height ratio (VF) of 0.06-5.40, and evaluation of relative tectonic activity (Iat) of 1.6-2.6. Results showed that river morphology and geomorphological indices in the Longchuan River basin were influenced by tectonic activity, bedrock lithology, climatic conditions, and development time, with tectonic activity playing a dominant role. The relative tectonic activity of the Longchuan River basin was zoned, with a gradual increase in relative tectonic activity from the south to the north. That the slip fault zone primarily controls the tectonic deformation of the Longchuan River basin in central Yunnan and the dynamics of the central Yunnan massif are consistent with the "rigid block lateral extrusion" 1model.