The regional structure of the turanian platform and its development

Abstract

The major features of regional structure and development of the Turanian platform are the result of the interaction of basement block movements with surrounding mobile belts. Some specific features, typical of the geosynclinal stage, can also be observed in the intermediate and platform stages. These features include subdivision of region by linear and smooth brachyform structures and the more pronounced irregularity in development of the former compared with the latter. The position of the most mobile elements of the Turanian platform are observed to migrate. As the intensity of movements in South Tien Shan—Kysylkum Hercynian branch (in the basement) decreased and activity of the Alpine geosyncline and postplatform orogene increased, the most mobile zone moved from the central and southeastern parts of the platform towards the southern and eastern periphery. Changes in the rates of sedimentation and growth of the majority of regional structures of the Turanian platform have a tendency to occur in opposite senses. The time of general subsidence in the Cretaceous corresponds to a decrease of growth rate of many structures. General platform upheaval during the recent phase coincides with an increase of structural growth. In peripheral and central aulocogen parts of the platform, stabilized or activated during the Jurassic, similar variations of sedimentation and growth rates are observed. The minor mobility of the biggest uplifts in comparison with the downwarps (except for the recent phase) indicates the predominance of continuous, general extension of the Turanian platform with an increase in the role of compression in Oligocene—Quaternary time. An almost equal number of regional structures of the Turanian platform occur with respectively conformable and unconformable relationship between the tectonics of the basin floor and that of the Moho. Beneath the structures developed in the southwestern mobile part of the platform deep crustal tectonics is a result of a long period of deformation during platform and intermediate stages. In the stable northeastern part of the platform crustal deformation during the platform stage was insignificant. The crustal tectonics here is probably a relic of Paleozoic pre-platform development.