Active faults and crustal stress in the northeastern flank of the Baikal rift system

Abstract

We discuss the patterns of Late Cenozoic faulting and crustal stress in the northeastern flank of the Baikal rift system. The Late Cenozoic faults are mainly of NE and ENE strikes. Faults of these trends, along with W–E faults, have been principal seismogenic structures. They have normal or left-lateral oblique geometry with different amounts of horizontal motion. The N–S, NW, and NNW faults bear signature of mostly right-lateral strike slip, and those of the WNW direction are left-lateral strike-slip faults, often with a normal component. The rift basins in this part of the rift system have had different evolution dynamics, with the most rapid faulting and sedimentation in the Muya basin. According to structural and seismological data, regional stress in the area has been stable and dominated by NW extension through the Pleistocene-Holocene and the Present. The directions and obliquity angles of principal normal stresses and percentages of stress types show local lateral variations. The evolution of the northeastern flank of the Baikal rift system can be explained by a model of oblique rifting which accounts for the architecture of rift basins, the pattern of Late Cenozoic active faults, and the stress pattern derived from structural and seismicity data. The model is consistent with centrifuge models of magma emplacement during continental oblique rifting. Oblique extension associated with underplated magma can be maintained in the area by mantle plumes beneath the Kichera, Upper Angara, and Chara rift basins. The presence of subcrustal magma chambers may explain why the three basins formed before other basins in the NE flank of the rift system.