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

Abstract. We model the recent detbnnation 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 theological 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 theological 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 o 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)• 1