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).