An attempt is made in this paper to outline the general tectonic development of platforms. We hope that such a review will help to determine the directions which geological-geophysical research should take within the Upper Mantle Project. We apply the term platform, a synonym of craton, to any large portion of the continental crust bounded by folded belts or sometimes by oceans, and characterized by the following specific features: (a) tectonic stability over a very long period (several hundreds of million years or more); (b) general tectonic homogeneity (despite a complex inner structure and different times of formation of its separate parts); (c) an absence of high gradients of movement. Shields are elements of platforms which have been characterized by a tendency towards slow uplift over periods of hundreds of million years. They are not sharply delimited. We have accepted the following ages for the upper boundaries of Precambrian units: Archaean 2,600-2,800 m.y. (million years); Lower Proterozoic (Palaeoproterozoic, according to Salop) 2,100 m.y.; Middle Proterozoic (Mesoproterozoic) 1,850-1,650 m.y.; Upper Proterozoic (Neoproterozoic) 1,100 m.y.; Epi-Proterozoic (Epiproterozoic) 620 m.y.; Eocambrian 570 m.y. The authors believe, although the material here presented is based mainly on studies of Eurasian structures, that these results can be also applied to all other continents. Reference to data on other areas is always stipulated. © 1969.
