The Earth's core formation and development: evidence from evolution of tectonomagmatic processes and paleomagnetic data

Many geologists confident that the core provides modern tectonic and magmatic activity on the Earth, which explains our interest in this topic, and vice versa we can use evolution of tectonomagmatic processes throughout the Earth's (and other terrestrial planetary bodies) history for reconstruction of the core formation and evolution. Most researchers, follow to V. Safronov (1972) and A. Ringwood (1979), confident that the Earth has occurred due to accumulation of hypothetical chemically homogeneous planetesimals, composed by chondrite material, ie, as a result of homogeneous accretion. However, this single-stage chondrite model of accretion is inconsistent with fact of cardinal change of tectonomagmatic processes on the terrestrial planets in the middle stages of their development. For example, the critical irreversible change of the Earth's tectonomagmatic evolution occurred in range 2.35-2.0 Ga, when geochemical-enriched Fe-Ti picrites and basalts firstly appeared in large quantities and first geological evidence of plate tectonics showed up (Sharkov, Bogatikov, 2010). We suggest that these changes were linked with ascending of mantle superplumes of the second generation (thermochemical), originated at the the boundary of liquid iron core and silicate mantle, in similar way as the modern plumes. All terrestrial planetary bodies (Earth, Venus, Mars, Mercury, and the Moon) have a similar structure, consist of iron core and silicate envelope, and developed at the same scenario, which provide for drastic irreversible change in character of tectonomagmatic processes at the middle stages of their evolution (Sharkov, Bogatikov, 2009). Such a situation can be realized only in case: (1) the terrestrial planetary bodies originally had heterogeneous structure, and (2) their heating occurred from the top down accompanied by cooling of outer shells. As a result, material of the primordial cores, where enriched material survived, were remained a long time untouched. It assumes the Earth (and other terrestrial planets) occurred by heterogeneous accretion from the material that existed in the early Solar system with primordial iron cores as embryos. Material of this core can be activated only as a result of its melting which fit with paleomagnetic data on the Earth, where magnetic field strength culminated practically simultaneously with beginning of the tectonomagmatic activity change. However, magnetic field on the Earth was existed at least from 3.5 Ga (Tardino et al., 2010) evidence about liquid iron in its deep interior, considered with separation of low-temperature Fe+FeS eutectic from the chondritic primordial mantle. It sank through silicate matrix and accumulated on surface of still cool primordial core. However, it was not affected on tectonomagmatic processes, which occurred essential later. So, the modern (secondary) Earth's core is formed by mixture of the iron of chondrite origin and material of the primordial core which were intermixed by convection after melting of the latter. It agrees with Walker (2010) data that part of material of the terrestrial planets cores was not related to chondrite.