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Magmatism and metallogeny of the early Earth as a reflection of its geologic evolution

M. I. Kuzmin, V. V. Yarmolyuk, A. B. Kotov and N. A. Goryachev
Magmatism and metallogeny of the early Earth as a reflection of its geologic evolution
Russian Geology and Geophysics (December 2018) 59 (12): 1535-1547


The paper is focused on the evolution of the Earth starting with the planetary accretion and differentiation of the primordial material (similar in composition to CI chondrites) into the core and mantle and the formation of the Moon as a result of the impact of the Earth with a smaller cosmic body. The features of the Hadean eon (ca. 4500-4000 Ma) are described in detail. Frequent meteorite-asteroid bombardments which the Earth experienced in the Hadean could have caused the generation of mafic/ultramafic primary magmas. These magmas also differentiated to produce some granitic magmas, from which zircons crystallized. The repeated meteorite bombardments destroyed the protocrust, which submerged into the mantle to remelt, leaving refractory zircons, indicators of the Early Earth's geologic conditions, behind. The mantle convection that started in the Archean could possibly be responsible for the Earth's subsequent endogenous evolution. Long-living deep-seated mantle plumes could have promoted the generation of basalt-komatiitic crust, which, thickening, could have submerged into the mantle as a result of sagduction, where it remelted. Partial melting of the thick crust, leaving eclogite as a residue, could have yielded tonalite-trondhjemite-granodiorite (TTG) melts. TTG rocks are believed to compose the Earth's protocrust. Banded iron bodies, the only mineral deposits of that time, were produced in the oceans that covered the Earth. This environment, recognized as LID tectonics combined with plume tectonics, probably existed on the Earth prior to the transitional period, which was marked by a series of new geologic processes and led to a modern-style tectonics, involving plate tectonics and plume tectonics mechanisms, by 2 Ga. The transitional period was likely to be initiated at about 3.4 Ga, with the segregation of outer and inner cores, which terminated by 3.1 Ga. Other rocks series (calc-alkaline volcanic and intrusive) rather than TTGs were produced at that time. Beginning from 3.4-3.3 Ga, mineral deposits became more diverse; noble and siderophile metal occurrences were predominant among ore deposits. Carbonatites, hosting rare-metal mineralization, could have formed only by 2.0 Ga. From 3.1 to 2.7 Ga, there was a period of "small-plate" tectonics and first subduction and spreading processes, which resulted in the first supercontinent by 2.7 Ga. Its amalgamation indicates the start of superplume-supercontinent cycles. Between 2.7 and 2.0 Ga, the D" layer formed at the core-mantle interface. It became a kind of thermal regulator for the ascending already tholeiitic mantle plume magmas. All deep-seated layers of the Earth and large low-velocity shear provinces, called mantle hot fields, partially melted enriched EM-I and EM-II mantles, and the depleted recent asthenosphere mantle, which is parental for midocean-ridge basalts, were finally generated by 2 Ga. Therefore, an interaction of all Earth's layers began from that time.

ISSN: 1068-7971
Serial Title: Russian Geology and Geophysics
Serial Volume: 59
Serial Issue: 12
Title: Magmatism and metallogeny of the early Earth as a reflection of its geologic evolution
Affiliation: Russian Academy of Sciences, Siberian Branch, A.P. Vinogradov Institute of Geochemistry, Irkutsk, Russian Federation
Pages: 1535-1547
Published: 201812
Text Language: English
Publisher: Allerton Press, New York, NY, United States
References: 51
Accession Number: 2022-003832
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Russian Academy of Sciences, Institute of Geology of Ore Deposits, RUS, Russian Federation
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2022
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