Long-term throw rates and landscape response to tectonic activity of the Tunka Fault (Baikal Rift) based on morphometry

Abstract

Determining the fault displacement rates and the sequence of formation of intra-rift structures are essential aspects in the study of the evolution of intracontinental rifts. To better understand the development of the Tunka system of basins (Baikal Rift) and the influence of tectonics on landscape evolution, we conducted a morphometric analysis of the Tunka Fault and its transverse drainage network. We studied geomorphic parameters of 64 facets and 74 drainage basins within the Tunka mountain-front in the footwall of the Tunka Fault; these parameters include mountain front sinuosity, the ratio of facet height and width to base length, basin shape, hypsometric integral, asymmetry factor, and the valley width to height ratio. Our main objectives were to determine long-term throw rates for specific mountain front segments and estimate the timing of corresponding geomorphic structures, to characterize the geomorphological response of the transverse drainage systems to fault movements, and to understand the relationship between the morphometry and kinematics of different segments along the Tunka Fault. The analysis of the Tunka mountain front reveals evidence for strong tectonic control on its morphology. We found that the morphological features are strongly influenced by the Late Pleistocene – Holocene kinematic inversion along the eastern part of the Tunka Fault. The Late Pliocene–Quaternary throw rates estimated for specific geomorphic structures vary in the range of 0.8–1.0 mm year−1, which is compatible overall with the long-term throw rates of other basins of the Baikal Rift. Based on these rates, we estimate the age of fault-controlled subsidence of the Tunka and Khoytogol basins and Nilovsky Spur to be between 3.5 and 1.5 Ma. We also show that geomorphological response of the transverse drainage varies along the Tunka Fault, indicating a close relationship between fault kinematics and landscape response.