THE IRTYSH ZONE OF DEFORMATION AND ITS RELATION TO DEEP RIFTS

According to Nekhoroshev the Irtysh zone is a deformation belt of foliated rocks 20 km wide associated with a major thrust between the axial and marginal portions of the Zaysan geosyncline. The author believes the Irtysh zone is composed of a horst-like anticlinal zone of Devonian metamorphics 25 km-50 km wide and a fault zone 1 km-3 km wide which is described in detail. It is interpreted as originating in the Precambrian and to have been a profound rift. Its microstructure as revealed in rocks of diverse types are discussed in detail. The history of the rift zone as recorded by the rocks involved covers much of Paleozoic to Cenozoic time. It is interpreted as intracrustal and not extending below the sialic layer. The geologic history of the zone is described in considerable detail. B. N. Cooper