A New Type of Tectonic Structure

摘要

Independent structural units called epigons, or epigonals are discussed. These structures were developed after the stage of completed folding, and at some points upon areas of PreCambrian platform, or directly after the geosynclinal stage. Although formally epigons do possess a combination of features of geosynclinal and platform development, they are independent structures of the first order. One of the most characteristic of such structures is the West Transbaikal mobile zone. Within this zone, in the Lower Mesozoic, there took place an intensive magmatic activity, processes of fold formation, emplacement of a variety of intrusions. The deposits are, in the main, heterogeneous lava effusions and clastic formations of volcanic origin. Normal sedimentary deposits are rare. This zone was formed in a region that had successively passed through the Baikal stage of folding (about 1000 million years ago) the Caledonian stage (600 million years ago) and Hercynian stage (about 400 million years ago). The development of epigonal regions was characterized by a slow downwarping and the accumulation of the thick volcanogenic deposits, as would be appropriate for the initial stages of geosynclinal development.