Coupling of late cenozoic faulting of the Siberian Platform margin and Baikal Rifting

Abstract

The relationship between the Late Cenozoic tectonic deformations at the Siberian Platform (SP) margin and the adjacent Baikal Rift System is considered. This study was aimed at estimation of the stress state and conditions of neotectonic reactivation of faults in the sedimentary cover of the eastern Irkutsk Amphitheater (the Angara‐Lena Uplift and Fore-Baikal Trough coupling zone). On the basis of geological, structural, and geomorphic methods, the Late Cenozoic fault assemblages were investigated and the related stress field was reconstructed to provide evidence for interrelated deformation of the Baikal Rift and the SP margin. The dynamic interaction of the SP block with the surrounding fold systems at the neotectonic stage and the evolution of the Late Cenozoic faulting remain poorly studied. A.G. Zolotarev developed the concept of fore-rift troughs [5 among others]. The brittle fracturing of the upper Pleistocene sediments was documented in the Fore-Sayan Foredeep [1, 8]. The existence of recent seismic activity of the platform has been proven in [2]. Seminsky et al. [8 and others] attempted to demonstrate the interrelation between the seismic activity and deformations in the Baikal Rift. However, these issues remain insufficiently studied because of short-term instrumental measurements and the absence of seismic station network on the platform. The northeastern part of the Irkutsk Amphitheater of the SP is characterized by medium-intensity neotectonic uplifting with an amplitude of 800 m relative to the initial surface [4]. Such values have been estimated for the Angara‐Lena Uplift. The Fore-Baikal Trough, which extends on the eastern side along the SP margin, ascended less intensely (amplitude of vertical movements was not greater than 200 m). The difference in the present-day hypsometric position of these structures suggests a rather high velocity gradient of neotectonic vertical movements in their coupling zone, providing prerequisites for differential motions along fault zones. The schematic map of faults in the Fore-Baikal Trough and Angara‐Lena Uplift coupling zone (Fig. 1) is based on the interpretation of satellite images and aerial photographs, analysis of a digital 3D model of topography, results of field geostructural and geomorphic observations, and compilation of the State Geological Mapping data. The faults in the study territory make up a rather dense network in comparison with inner sectors of the SP, probably owing to the closeness with the Sayan‐ Baikal mobile region. Paleozoic folds and faults significantly controlled the development of local neotectonic structures. The northern part of the territory is dominated by submeridional faults that reflect the general strike of older linear structures in the study region (Kirenga fold zone [3]). The NE-trending faults inherit structures of the Zhigalovo‐Tulukmur fold zone. The neotectonic reactivation stage is characterized by nonuniform manifestation over the study area (Fig. 1). Judging from the density of neotectonic faults, the northern Fore-Baikal Trough and the zone of its coupling with the Angara‐Lena Uplift were most active. The maximums of fault density are confined to the Khanda (southern end), Baldakhin’ya, and Novoselovo basins. The platformal sedimentary cover in the northern Angara‐Lena Uplift is marked by minimum faulting.