Dynamics of intracontinental extension in the north Baikal rift
from two-dimensional numerical deformation modeling

Lesne, O., E. Calais, J. Deverchère, J. Chéry, and R. Hassani, Dynamics of intracontinental extension in the Northern Baikal Rift zone, Siberia, using lithospheric-scale numerical models, J. Geophys. Res., Vol. 105, No. B9, 21,727-21744, 2000.


 Modern rifts offer the opportunity to better understand the processes that control continental breakup by comparing direct observations and measurements with theoretical models. Among the factors that contribute to the initiation and evolution of intracontinental rift zones, far-field stress in the lithosphere (horizontal traction), heat supply by mantle plumes or asthenospheric upwellings (basal traction), inherited zones of weakness in the lithosphere, and the rheological structure of the lithosphere are thought to be dominant.

We model the recent deformation along a lithospheric-scale cross section perpendicular to the northern part of the Baikal rift zone (BRZ) with two-dimensional finite element models. Using realistic lithospheric structure and rheological properties and imposing extension as a far-field boundary condition, we find a model that matches reasonably well the topography, observed deformation pattern, gravity anomalies, and age of formation of the northern BRZ. Our results suggest that (1) extensional strain can occur away from the main rift basin in the Sayan Baikal range and create, depending on the rheological properties of the lithosphere, a large "off-rift" basin analogous to the Barguzin basin, or a series of basins and ranges, as observed in the southern part of the Sayan Baikal range, (2) anelasticity plays a major role by participating in the uplift of rift shoulders and hanging wall deformation, and allowing the subsidence and tilting of the hanging wall along high-angle planar normal faults, (3) the lower crust accommodates differential strain between the brittle upper crust and upper mantle by horizontal shear and lateral flow towards the regions of crustal and mantle thinning, (4) far-field extensional stress and a lithospheric discontinuity inherited from Paleozoic tectonic events are sufficient to initiate rifting and basin subsidence, and (5) there is no, or very little, dynamic contribution of a hypothetic asthenospheric plume under the BRZ, at least in the recent phase of its evolution ("fast rifting stage", 3.5 Myr).