Earth’s earliest granitoids are crystal-rich magma reservoirs tapped by silicic eruptions

Granitoids of the tonalite–trondhjemite–granodiorite (TTG) series dominate Earth’s earliest continental crust. The geochemical diversity of TTGs is ascribed to several possible geodynamic settings of magma formation, from low-pressure differentiation of oceanic plateaus to high-pressure melting of m...

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Bibliographic Details
Published in:Nature geoscience 2020-02, Vol.13 (2), p.163-169
Main Authors: Laurent, Oscar, Björnsen, Jana, Wotzlaw, Jörn-Frederik, Bretscher, Simone, Pimenta Silva, Manuel, Moyen, Jean-François, Ulmer, Peter, Bachmann, Olivier
Format: Article
Language:English
Subjects:
140/146
704/2151/209
704/2151/213/4114
704/2151/431
704/2151/598
Basalt
Complementarity
Continental crust
Crystallization
Crystals
Differentiation
Earth
Earth and Environmental Science
Earth crust
Earth Sciences
Earth System Sciences
Eruptions
Fossils
Geochemistry
Geochronology
Geochronometry
Geology
Geophysics/Geodesy
Igneous rocks
Isotopes
Lava
Liquids
Low pressure
Magma
Magma chambers
Melting
Nucleation
Organic chemistry
Petrography
Phanerozoic
Plagioclase
Plate margins
Plateaus
Plutons
Pressure
Reservoirs
Rocks
Sciences of the Universe
Segregation
Uranium
Volcanic eruptions
Volcanic rocks
Volcanology
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Summary:Granitoids of the tonalite–trondhjemite–granodiorite (TTG) series dominate Earth’s earliest continental crust. The geochemical diversity of TTGs is ascribed to several possible geodynamic settings of magma formation, from low-pressure differentiation of oceanic plateaus to high-pressure melting of mafic crust at convergent plate margins. These interpretations implicitly assume that the bulk-rock compositions of TTGs did not change from magma generation in the source to complete crystallization. However, crystal–liquid segregation influences the geochemistry of felsic magmas, as shown by the textural and chemical complementarity between coeval plutons and silicic volcanic rocks in the Phanerozoic Eon. We demonstrate here that Paleoarchean (ca. 3,456 million years old) TTG plutons from South Africa do not represent liquids but fossil, crystal-rich magma reservoirs left behind by the eruption of silicic volcanic rocks, being possibly coeval at the million-year scale as constrained by high-precision uranium–lead geochronology. The chemical signature of the dominant trondhjemites, conventionally interpreted as melts generated by high-pressure melting of basalts, reflects the combined accumulation of plagioclase phenocrysts and loss of interstitial liquid that erupted as silicic volcanic rocks. Our results indicate that the entire compositional diversity of TTGs could derive from the upper crustal differentiation of a single, tonalitic magma formed by basalt melting and/or crystallization at
ISSN:1752-0894
1752-0908
DOI:10.1038/s41561-019-0520-6