Geological Timescale of Tectonostages for Continental Margins

The lithosphere plate tectonics theory describes the process of oceanic crust opening and closure in geological history of the Earth using the Wilson cycle. Upon the end of the cycle, the oceanic crust being formed at its early stages is almost completely destructed in the process of subduction. As for the continental margin, it is modified during the cycle with formation of volcanic and non-volcanic island arcs, back- and fore-arc sedimentary basins, and orogens. During the next stage of the cycle, the previously formed continental margin is again affected by deep transformation, leaving in the structure of the newborn margin only some relics of the previous ocean crust known as ophiolites. However, as the study proves, complete destruction of the previous continental margin is not reached. Always or quite often a significant part of the newborn continental crust is preserved and laterally accreted to an existing continental plate and is being modified during further transformations passing through consecutive stages that could be called a vertical line of the tectonostages for particular continental margin. Evidence for that conclusion is an age rejuvenation of the continental crystalline crust while moving from the central parts (shield) towards their outskirts (continental margin). It is proposed a geological timescale of tectonostages derived from the Wilson cycle and establishing their time boundaries for the last 2500 million years. Along with the developed model for continental margins evolution, it allows application of the concept of horizontal sequence of tectonostages transition into vertical and vice versa to study structure of continental margins. It is supposed that for the Wilson cycle of 1200 million years every continental margin is subjected to the tectonic process as follows. During the first stage of a divergent epoch (0-200 Ma), a new oceanic basin is forming due to a continental rift. Present-day example of such a rift one can consider the Red Sea Rift and latitude-oriented rift system between North and South America stretched into the Pacific and Atlantic Oceans. Predecessor of the future Red Sea Ocean were the Tethys and the Prototethys paleo-oceans, which originated during the stages of 590, 75-385, 75 Ma and 992,5-793,0 Ma ago. The Tethys is corresponding to present-day Alpine-Himalayan orogenic zone and related sedimentary basins, and the Prototethys – to the Donbass Foldbelt and its eastern prolongation into Karpinskiy Ridge. Rejuvenation of continental margins age towards the periphery of the continents set the problem of studying evolution of those margins applying concept of vertical and horizontal sequences of tectonostages. For this purpose, the model of evolution (tectonic stratification) of continental margins is developed. It includes six stages of tectonic evolution: origination of a new ocean and its opening (divergent epoch of the Wilson cycle), stage of the oceanic basin shortening and thermal subsidence (convergent stage), stage of partial inversion, and the next stage of the complete inversion along with the compression thrusting (collision stage). Corresponding to the stages are the types of crust being formed (ocean, quasi-ocean, quasi-continental, continental). The stages are divided into geosynclinal and orogenic sub-stages (the Bertran cycle). It is demonstrated that tectonostages and orogenies are matching (Alpine, Hercynian, Caledonian, Baikal and others) for the last 1500 million years. Actually, the features and direction of changes in vertical and horizontal sequences of continental margin tectonostages is a basic tectonic regularity to be studied because it determines existing types of sedimentary petroleum-prone basins, sedimentary complexes and separate prospects considered as hydrocarbon traps.