Genesis and evolution of magmas according to data on hot heterogeneous accretion of the Earth

The obtained numerous proofs of hot heterogeneous accretion of the Earth lead to a fundamentally new solution to the problems of genesis and evolution of magmas. According to these data, the Earth’s core was formed earlier than the silicate mantle as a result of the agglutination of iron particles of the protoplanetary disk under the influence of magnetic forces, because with a small body size, these forces were billions of times more powerful thangravitational ones. The accretion of the silicate mantle created a global magmatic ocean under the influence of impact heat release. Its bottom part crystallized and fractionated as a result of the pressure increase of the formed upper parts. Cumulates formed the ultrabasic mantle, and residual melts formed the magmatic ocean. The increase in ocean temperature and depth caused the evolution of bottom residual melts from acidic to ultrabasic, the appearance of corresponding layers in the ocean, and the reverse geothermal gradient in the mantle. As a result of the cooling and crystallization of the ocean from top to bottom after 3.8 billion years ago early Precambrian crystal complexes, acidic crust, and the lithosphere of ancient platforms were formed. The separation of residual melts from various layers caused the evolution of magmatism on them from acidic to akaline-ultramafic and kimberlite. Heating of the mantle by a high-temperature core led to the appearance of a direct geothermal gradient at the end of the Proterozoic, convection in the mantle, and modern geodynamic environments. In them, magmas are formed by the frictional and decompression melting of the differentiates of the magmatic ocean.

Генезис магм с позиции горячей гетерогенной аккреции Земли

The obtained numerous proofs of hot heterogeneous accretion of the Earth lead to a fundamentally new solution of the magma genesis problem. According to these data, in the course of the silicate mantle accretion, the global magmatic ocean emerged under the impact heat emission. Its bottom part crystallized and fractionated as a result of the pressure increase of the upper parts being formed. Cumulates formed the ultrabasic mantle; residual melts, the magmatic ocean. The increase in ocean temperature and depth caused the evolution of bottom residual melts from acidic to ultrabasic, the appearance of corresponding layers in the ocean, and the reverse geothermal gradient in the mantle. The top-down cooling and crystallization of the ocean, 3.8 billion years ago, Early Precambrian crystal complexes, acidic crust, and the lithosphere of ancient platforms were formed. The separation of residual melts from various layers determined the evolution of magmatism from acidic to alkaline-ultramafic and kimberlite. Heating of the mantle by a high-temperature core resulted in the appearance of a direct geothermal gradient at the end of the Proterozoic, convection in the mantle, and modern geodynamic environments. In the latter, magmas are formed by the frictional and decompression remelting of the magmatic ocean differentiates.

Origin of large diamonds in kimberlite

The evidence of the existence and fractionation of the global magmatic ocean on the Earth allows us to distinguish two stages of the formation of diamonds of increased size. The largest giant diamonds arose at an early stage of crystallization and fractionation of the peridotite layer of the magmatic ocean, since its bottom layer at that time was blocked by still hot upper ones and therefore cooled and crystallized very slowly and long. The mafic composition of this layer and the low viscosity of its magmas caused mainly octahedral cutting of the formed giant diamonds. Later crystallized mainly rhombododecahedral diamonds have increased coarseness due to the formation mainly by the growth of early octahedral crystals.

Genesis of Early Precambrian crystalline complexes

The obtained evidence of hot heterogeneous accretion of the Earth leads to a fundamentally new solution of the problem of the genesis of Early Precambrian crystal complexes. According to this approach, a powerful impact heat release during accretion resulted in the formation of a layered global magmatic ocean. Its upper acidic layer arose from low-pressure residual melts of the bottom parts of the still shallow early ocean, fractionated under the influence of an increase in the load pressure of the forming upper layers. The solidification of the uppermost parts of the acidic layer led to the formation of the most ancient tonalite-trondyemite complexes. Gneiss-crystalshale complexes were formed from its deeper parts by lowering the crystallized near-surface areas together with sediments accumulated on them and lifting the underlying magmas of often more mafic composition in their place. Leaching of the near-surface parts of the solidified rocks under the influence of acidic emanations of the magmatic ocean caused the predominance of quartzites and high-alumina gneisses among the oldest pararocks. Due to the solidification of the magmatic ocean from top to bottom, the isotopic age of gneiss decreases on average with depth. The surfacing of residual melts of its various layers led to the evolution of magmatism of ancient platforms from acidic to alkaline-ultrabasic and kimberlite. The separation of ore-bearing emanations of the magmatic ocean caused the formation of numerous often unique deposits.