THE BAIKAL RIFT: AN EXAMPLE OF THE INTRUSION OF ASTHENOSPHERIC MATERIAL INTO THE LITHOSPHERE AS THE CAUSE OF DISRUPTION OF LITHOSPHERIC PLATES

Abstract

The development of the Baikal rift zone is an initial stage in the break-up of the Eurasian plate. In this zone the anomalous mantle is found under the crust. It is characterized by decreased seismic velocity, decreased density and high temperature. These physical properties suggest that this anomalous mantle is an asthenospheric intrusion some 250–300 km wide. As the Baikal rift represents an extension of the first tens of kilometres, the appearance of the anomalous mantle is not regarded as the result of extension. It is more likely that the asthenospheric intrusion into the lithosphere was the cause of extension and faulting. If intrusion began about 30 m.y. ago and reached the base of the crust about 3 m.y. ago, the calculated temperature field is consistent with the present geophysically determined temperature distribution. Similar anomalous mantle occurs under other structurally similar crustal zones.