THE NATURE OF STRUCTURE AND EVOLUTION OF THE EARTH IN TERMS OF MODEL FOR FRACTIONATION OF THE MAGMATIC OCEAN DURING ITS FORMATION

On the basis of analysis of geological and petrological data, a new mo del has been derived for the origin and evolution of the Earth. The ev idence that the mantle matter is not in equilibrium with metal Fe sugg ests the earlier formation of the core, probably, because of great vel ocity of aggregation of magmatic particles. Low (0-5 kbar), medium- (5 -15 kbar) and high-pressure (15-70 kbar) stages were recognized during the synaccretionary bottom fractionation of the magmatic ocean result ed from impact melting. These stages correspond to the formation of ul trabasic cumulates of the lower, intermediate, and bottom of the upper mantle, with beds of residual melts composed of quartz tholeiite (24 km thick), high-alumina basalt (43.5 km), and picrite (172.5 km). The post-accrerionary fractionation of the layered ocean led to the format ion of cumulates in the middle part of the upper mantle, with lenses o f solidified alkaline-ultrabasic and alkaline-basic residial melts and acidic rocks of varying alkalinity, and granodioritic continental cru st more than 21 km thick. The subsequent friction and decompression re melting of products of solidification of residual melts led to the for mation of various compositionally identical magmas. The long-term exis tence of the magmatic ocean is responsible for the absence from the Ea rth of racks older than 4.1 Ga and traces of giant meteorite bombardme nt. The solidification of magma ocean in the Archean with the periodic al subsidence of the upper parts under cooling and the sediments that began to form led to the primary magmatic genesis and tonalite-granodi orite composition of the majority of gneisses, persistent high tempera ture character of their early metamorphism and many features of the Ar chean complexes. The subsequent cooling and condensation of the vapor shell led to stratiform deposits, to flooding of continents and format ion of their sedimentary cover. The cooling and thickening of the lith osphere account for increased height of mountains and depth of oceans in the Phanerozoic, increased role of brittle deformations, decreased temperature of regional metamorphism, and elevated middle depth of mag ma generation.