STRETCHING MARGINAL ZONES OF THE PRIPYAT PALEORIFT: GEOLOGICAL EVIDENCES OF A CANTILEVER MODEL. A. M. Kovkhuto, Institute of Geological Sciences, Minsk, Belarus.

The northern and southern marginal zones distinguished in the present-day structure of the Pripyat Paleorift developed in Devonian time separate the paleorift from the Ukrainian Shield on the south and from the Belarussian Anteclise on the north. The marginal zones may be regarded for the sake of simplicity as downthrown (paleorift marginal zones) and uplifted (paleorift shoulders) walls of marginal faults. The cantilever mechanism was working when the Northern and Southern marginal zones of the Pripyat Paleorift were developed. It was observed in the structure, tectonic pattern and evolution of the marginal zones. The North-Pripyat Shoulder differs from those of the other paleorifts as prerift and partly synrift deposits occur there, because it was a part of the paleorift at the initial rifting stage. The uplifted position of the North-Pripyat Shoulder is shown by paleoincisions as deep as 700 m that had formed in Late-Frasnian time. Slabs of the Ukrainian Shield upper part had been most likely thrusted over Upper Devonian sedimentary rocks, which is shown by a low-velocity zone revealed by geophysical surveys at a depth of 5-6 km in crystalline rocks ofthe Ukrainian Shield on the southern shoulder of the Pripyat Paleorift. The marginal zones acted as bounding limits of paleobasins during the Mesozoic and the more recent time.