INFLUENCE OF TECTONICS AND CLIMATE ON THE EVOLUTION OF FLUVIAL TERRACES: A CASE STUDY OF THE HONGSHUIBA AND MAYING RIVERS IN THE NORTHERN MARGIN OF THE QILIAN MOUNTAINS
In tectonically active regions,geomorphic features such as fluvial terraces can be interpreted as the consequence of tectonic and climatic forcing. However,deciphering and distinguishing tectonic impacts and climate changes remain a challenge. In this study,we examine the terraces along the Hongshuiba river and Maying river,which flow across the Fudongmiao-Hongyazi fault in the northern margin of the Qilian Mountains. Our purpose is to analyze the relative roles of tectonics and climate in shaping orogenic topography in this area. 8 ~ 9 levels of river terraces were identified through field observations,interpretation of satellite images and using DEMs. According to relative heights and ages of T_5 of the Hongshuiba river and T_6 of the Maying river,the incision rates are calculated to be (10.22.0) mm/a and (12.2 2.8) mm/a,respectively. Furthermore,the thrust rate along the Fodongmiao-hongyazi fault was determined based on offset terraces and OSL dating,which are ten times less than river incision rates approximately. Comparing the uplift rate and incision rate in the northern margin of the Qilian Mountains and adjacent areas,we inferred that climate change is the most plausible controlling factor in the evolution of the river terraces,while tectonics plays a minor role in this process.