STRUCTURE OF THE CRUST IN THE BAIKAL RIFT ZONE AND ADJACENT AREAS FROM DEEP SEISMIC SOUNDING DATA

Abstract

2-D P-wave velocity models of the crust along DSS profiles have been used together with 2-D seismic tomography for constructing maps of the Moho topography and average P-wave velocity in the crust in Baikal rift zone (BRZ) and adjacent areas. There are significant changes of Moho depth between 35 and 50 km but there is no pronounced crustal thinning beneath the rift axis. Instead, changes in crustal thickness appear to be related to accretion entities, including the transition between the Archean craton and the tectonic collage of the Transbaikal fold belt. Taking into account the decrease in resolution of the Deep Seismic Sounding (DSS) method with depth, it was found that the crust at a depth of approximately 20 km could be divided into two parts. The interval velocities in the upper and lower parts of the crust are inversely correlated, both within the craton and in the Transbaikal belt. Locally, this relationship does not hold and as such may be used to discriminate tectonic blocks. Velocity anomalies coincident with the position of the Baikal rift zone are distinctly seen in the upper part of the crust only.