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1 Acta Geophysica Polonica

1 1999

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Seismic structure of the crust-mantle transition zone of the Ukrainian shiels

Starostenko V., Kharitonov O., Tripolsky A.

Acta Geophysica Polonica

1999

Vol. 47, nr 2

185-201

The Ukrainian shield is one of the largest heterogeneities of the East European Platform. The deep seismic sounding results indicate a blocked layred structure of the shieldsand enabled us to separate several long submeridonal crustal blocks, notably differing from each other in thickness, which are cut deep falts of mantle origin. The geologic and geophysical features of these blokcs suggest that they belong to protoplatform structures with 38-51 km thick crust and protogeosynclines with Moho-discontinuity depth to 65 km. An analysis of dynamic characteristics of reflection waves shows that within the protoplatform blokcs the Moho-discontinuity is mainly a sharp boundary of the first order with longitudinal waves velocity contrast corresponding to the basic-ultrabasic rocks contact. In the protogeosynclinal systems, a 3-9 km thick crust-mantle transition zone is distinguished. By using of combinated kinematic-dynamic analysis for the Ukrainian shielld, several of acoustic models of the crust-mantle transition zone were distinguished. The nature of this zone may be either a gradual transition from mafic to ultramafic rocks or its origin may be results of the underplanting.