Upper mantle structure beneath southern Siberia and Mongolia, from regional seismic tomography

Tomographic inversion of ~130,000 P and ~11,000 S arrivals from 1045 events recorded by the world seismological network (ISC catalog data) has been applied to image the three-dimensional velocity structure of the upper mantle beneath the Baikal rift and Mongolia. The inversion-derived P and S velocity anomalies show a good agreement. At depths above 200 km, low-velocity zones occur along the contours of the high-velocity Siberian craton and in Mongolia and coincide with fields of Cenozoic volcanism. The deeper mantle appears quite homogeneous, with anomalies no greater than 0.5% and a single low-velocity feature beneath the Siberian craton. The tomographic image is poorly consistent with the hypothesis implying the existence of large mantle plumes under Mongolia which has been checked with synthetic tests. According to the tomography-based geodynamic model, volcanism in the East Sayan mountains may be induced by a hot plume rising from beneath the Siberian craton, but the source of volcanism in the area of Hangayn remains open to discussion.