HISTORY AND GEODYNAMICS OF THE BAIKAL RIFT

Abstract

The morphology, structural setting, and evolution of the Baikal rift system has been controlled by its position at the junction of the Siberian craton and the Central Asian mobile belt, two major tectonic units with contrasting thermomechanical properties. Rifting initiated in South Baikal, in place of the present Selenga delta, where first Late Cretaceous-Paleocene pulses of extension produced a large basin. The basin began to draw in the regional surface runoff as the Selenga valley broke through the Khamar-Daban Ridge and captured the drainage of Western Transbaikalia and Northern Mongolia inherited from the Late Mesozoic. Rifting propagated on both sides off South Baikal as far as the youngest rift basins and faults in Mongolia in the southwest and in the Olekma region in the northeast. The Baikal basin includes two rather than three structurally equal subbasins, South and North Baikal, separated by a diagonal link of Olkhon island — submerged Akademichesky Ridge — Ushkan'i isles. The South Baikal basin is in turn bisected by the Selenga saddle, the oldest and largest deposition center filled with about 10,000 m thick sediments strongly deformed in Pliocene-Quaternary time. The neotectonics, crustal thickness, and 3D velocity structure of the region between the rift and the India/Eurasia collision front indicate that rifting in East Siberia evolved under the joint effect of local and far-field geodynamic mechanisms.