Native Iron Nodules in Basites - Xenoliths of the Earth Core

Abstract

Abstract Summary of the published data has shown that native iron nodules, which are rarely found in the basic intrusions, are characterized by a higher content of low-temperature condensates of the protoplanetary disk (Ge, Ag, Cu) and a lower content of high-temperature condensates (Os, Ir, Ru, Pt, Rh, Pd, Ni, Co, Au) compared to iron meteorites. Such meteorites have signs of formation from the fragments of the cores of minor planets. This fact and obtained evidence of hot heterogeneous accretion of the Earth, the early formation of the Earth’s core compared to the mantle and the growth of the primary content of low-temperaGture condensates from the inner parts of the core to the outside suggest the capture and the ascent of substance of outer core by mantle plumes, and basic magmas formed in them. This explains the peculiarities of their composition, their very rare presence in basites, and sometimes a huge mass of nodules (up to tens of tons). In case of such xenogenic origin, nodules of native iron are chemically unequilibrium with basites. This is the reason of the development of reaction cohenite-magnetite and cohenite-sulfide rims on their contact and an increase of ferruginosity of olivine in basites. The formation of the lower mantle material from the earliest high-temperature condensates of the protoplanetary disk explains the decreased content of potassium, sodium, water, and other lithophile components in the nodule-containing basites. The content of volatile components lowers the crystallization temperature of melts. Therefore, the loss of them under the influence of decompression at the low-depth stages of ascent led to rapid solidification of magmas, protected the iron nodules from subsidence, and explains their location mainly in the upper parts of the main intrusions, despite the high density of iron.