The Early Earth, Formation and Evolution of the Lithosphere in the Hadean – Middle Archean

Arkady Pilchin, Lev Eppelbaum

Research output: Chapter in Book/Report/Conference proceedingEntry for encyclopedia/dictionarypeer-review

Abstract

Some physical problems related to modeling the conditions of the formation and evolution of the lithosphere are discussed. It is shown that if we take into account both the effects of thermal expansion and compressibility we could receive results with no change or even an increase of density under the P-T conditions within the lithosphere. During planetary accretion and differentiation of Earth, the planet could have been entirely molten and at some point of its evolution was entirely covered by a magma ocean. The formation and composition of the early lithosphere were mostly related to processes of the differentiation of matter and the rate of cooling of the magma ocean. The process of the differentiation of the magma ocean would begin during its formation and continue until its solidification. This stratification of the composition of Earth caused an initial state of separation of rocks and minerals into slabs within the upper mantle and crust, which was strictly regulated by their density, whether solid or melted. The difference in density between felsic, intermediate, mafic, and ultramafic magmatic slabs within the magma ocean was enough to prevent the exchange of matter between them, and therefore mantle-wide convection could not have taken place. The solidification of the magma ocean, upon which the process of the formation of the lithosphere is dependent, most likely began with the formation of forsterite (or forsterite-rich peridotite) slab at a depth of about 100 km followed by the solidification of Earth‘s surface, cooled by heat radiation from the surface and the cooling effect of the early atmosphere. It is shown that under the thermal conditions of the magma ocean, carbonate rocks were unstable and decomposed, releasing carbon dioxide into the atmosphere. Water could also not exist in its liquid state at the time of the magma ocean, and together with the carbon dioxide would form a thick and dense early atmosphere. Formation of the water ocean was under the constraints of the boiling point of water at the pressure of the early atmosphere and the critical point of water. Cooling rates of the magma ocean and the early lithosphere are discussed in comparison with the cooling rates of the mantle and numerous magmatic and/or metamorphic complexes. The main periods of the appearance of komatiites and the formation of the first large igneous provinces (LIPs) indicate temperature maximums in the mantle at about 2.8-2.7 Ga and a maximum volume of mafic magmatism related to the formation of LIPs at about 2.5 Ga. Analysis of the periods of the formation of granulites suggests an increase in temperature at a depth of about 30 km from ~3.0 Ga to ~2.7 Ga, with its continuing increase to ~2.5 Ga. It is shown that at the end of the Archean, the thickness of the lithosphere was ≤100 km, including a solid forsterite slab at ~100 km depth with possible pockets of magma above it.
Original languageEnglish
Title of host publicationENCYCLOPEDIA OF EARTH SCIENCE RESEARCH
EditorsFUMIO SATO, SHIGEO NAKAMURA
Place of PublicationNew York
PublisherNova Science Publishers, Inc.
Chapter1
Pages1-93
Number of pages93
Volume1
ISBN (Print)978-1-61470-247-4
StatePublished - 2012

Publication series

NameEarth Sciences in the 21st Century

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