Evolution of Faults in a Continental Rift: Morphotectonic Evidence from the Southwestern Termination of the North Baikal Basin

We studied the morphotectonic framework of the southwestern termination of the North Baikal basin including the Olkhon Island and its surroundings located in the central part of the Baikal Basin. The morphotectonic pattern of the region is produced by a distal series of en-echelon structures along strike and of lateral series of rift faults consisting of several parallel distal series of structures. The lateral series of faults in the Olkhon Region includes four successive distal series of structures arranged in the seaward direction as: Primorsky fault zone, Buguldeika-Chernorud graben-Maloye More rift basin-Ushkaniy fault zone, Tazheran Plateau-saddles of Olkhon Island and submerged Akademichesky ridge; Olkhon fault zone. The distal series are cut by transverse faults into a sequence of separate segments with their age increasing progressively northeastward with the youngest ones at the southwestern end. The vertical offset of the faults in the segments increases in the same direction from tens of meters to over 2000 m, and the fault zones become broader and acquire a more complex structure. The Primorsky fault zone changes northeastward from a simple linear fault scarp at its southwestern end to a system of fault-bounded blocks, then to a system of uplifted and subsided blocks (basins), and finally grading into a basin; the rift border faults are changed suddenly into within-basin structures in the same direction. This pattern of morphotectonic structures records the space and time evolution of faults, which are subject to progressive subsidence and broadening to finally develop into basins. Following this tendency, in the conditions of a lake basin, land structures eventually become submerged marine ones. The tendency of submergence of land structures and formation of within-basin structures out of tilted fault-bounded blocks may be a common feature of continental rifting associated with rotational listric faulting and controlled by general rift opening.