Dizhi lixue xuebao (Dec 2023)
Geomorphic features of the Menyuan basin in the Qilian Mountains and its tectonic significance
Abstract
The Qilian Mountains are situated on the northeastern margin of the Tibetan Plateau and serve as the leading edge of the plateau's northeastward expansion. The Menyuan Basin, characterized by typical basin landforms, provides valuable insights into the region's neotectonic activity and geomorphic evolution. As a representative mountain basin located in the central part of the Qilian Mountains, the Menyuan Basin's development pattern and geomorphic features are closely linked to tectonic activity. This study aims to investigate the variations in tectonic activity and their underlying causes along the north margin fault and different zones of the Menyuan Basin. To achieve this, 30 m resolution digital elevation model (DEM) data and ArcGIS spatial analysis technology were employed to extract the hypsometric integral (HI) and hypsometric integral curve (HC) of 15 rivers that traverse the northern edge of the basin. Subsequently, kriging interpolation was utilized to obtain the spatial distribution characteristics of HI within the basin. The findings reveal that HI values generally exhibit higher values on the western side and lower values on the eastern side of the Menyuan Basin, with the turning point (Laohugou) of the northern fault at the Menyuan Basin serving as the boundary. By combining the distribution of HI with field investigation results of active structures, it is observed that the eastern fault has extended into the basin's interior, giving rise to a series of active reverse fault–fold zones. This phenomenon may be attributed to changes in fault trends and the presence of northeastward faults. Additionally, a high HI anomaly is detected near Qingshizui Town in the basin's interior. Based on previous electromagnetic detection results, it is inferred that a buried fault exists within the basin. Furthermore, the study demonstrates that most rivers exhibit peak fluctuations in the stream length–gradient index (SL) at a specific position upstream of the main fault, indicating a strong correlation between the location of SL fluctuations and the position of the fault intersecting the river. In other words, tectonic activity can exert a significant influence on SL. Abnormal fluctuations near lithological transitions may suggest that local changes in lithology also impact the stream length-gradient index. The comprehensive analysis underscores the substantial differences in geomorphic development between the eastern and western sections of the northern edge of the Menyuan Basin, primarily controlled and influenced by the active structures in this region. Moreover, the aforementioned geomorphic parameters serve as sensitive indicators for evaluating tectonic activity.
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