Hierarchic features of stress field in the Baikal region: Case study of the Buguldeika Fault Junction

Abstract

The hierarchy of stress patterns at different evolution stages of the Central Baikal region has been studied by structural-genetic analysis of faults of different size ranks combined with other tectonophysical methods. Structural measurements were performed in the zones of the Primorsky, Olkhon, Prikhrebtovy, Buguldeika, and Kurtun faults that meet at the Buguldeika junction in the northwestern shore of Lake Baikal. Tectonic stress fields were reconstructed at the local, subregional, and regional levels in three largest fault zones (Primorsky, Olkhon, and Prikhrebtovy) and at the local and subregional levels in the smaller faults of Buguldeika and Kurtun. The stress settings in the area of the Buguldeika fault junction changed in the course of its tectonic history from Paleozoic-Mesozoic compression to Early Cenozoic strike-slip and finally to Late Cenozoic extension. The principal horizontal stress σ1 during the compression stage was oriented mainly in the NW and N–S directions. The Mesozoic N–S compression maintained northward propagation of imbricate thrusts from the Angara River headwaters as far as the Buguldeika area. The stage of strike-slip stress with N–S σ1 and W–E σ3 principal directions was reconstructed from structural measurements combined with slickenside data in the Primorsky fault zone and from slickenside data only in the Olkhon and Prikhrebtovy faults. The results show prolonged left-lateral strike-slip motions with large amounts of displacement in the Primorsky fault which delineates the Siberian craton margin. The Late Cenozoic extension stress setting has been modeled in terms of fan-like opening of large faults and clockwise rotation of upper crust blocks in the Central Baikal region.