Control of lithospheric structure and plate kinematics on rift architecture and evolution: An experimental modelling if the Baikal Rift

Analog models investigate the evolution and architecture of the Baikal rift in relation to the rheology of the extending lithosphere and rift kinematics. The models focus on the development of the narrow, deep, and asymmetric basins composing Lake Baikal and reproduce the extension between the strong Siberian craton and the weaker Sayan-Baikal belt. Model results suggest that the presence of a near-vertical weak suture separating the cratonic keel from the mobile belt represents the more convenient rheological configuration leading to a narrow rift characterized by prominent vertical motions and deep depressions. These depressions are typically asymmetric, and model results suggest that this asymmetry is a consequence of lateral variations in lithospheric rheology, which is in turn related to both the variation in thickness of the strong mantle and, more importantly, the variation in the brittle-ductile transition depth between the craton and the belt. A significant shallowing of the brittle-ductile transition in the crust passing from the craton to the belt is required to fit the asymmetric architecture of the Baikal basins, with a master fault on the craton side and a monocline with no significant faulting on the belt side. Analysis of the model deformation pattern suggests that the overall architecture of the basins hosting Lake Baikal is best fitted for a N140°E directed extension, similar to the current GPS-derived motion and compatible with the stress field inferred on the basis of fault and focal mechanism data. This kinematics (along with the shape of the Siberian craton) exerted the major control on the plan view fault architecture and its along-axis variations.