Archaean continental crust formed from mafic cumulates
Matthijs A Smit1,2, Kira A Musiyachenko3, Jeroen Goumans3
1Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2207 Main Mall, Vancouver, V6T 1Z4, Canada. msmit@eoas.ubc.ca.
Nature Communications
|January 24, 2024
Summary
Early continental crust growth involved tonalite-trondhjemite-granodiorite (TTG) magmatism. New research reveals TTGs formed from melting cumulates in proto-continental roots, explaining Archaean crustal evolution without external triggers.
Area of Science:
- Geochemistry
- Petrology
- Archaean Geology
Background:
- Tonalite-trondhjemite-granodiorite (TTG) magmatism was crucial for early continental crust growth and cratonisation.
- The petrogenesis, tectonic setting, and sources of TTGs remain poorly understood.
Purpose of the Study:
- Investigate the composition and petrogenesis of Archaean TTGs.
- Utilize high field-strength-element systematics to understand TTG formation.
Main Methods:
- Analysis of Nb concentrations and Ti anomalies in TTGs.
- Examining amphibole and plagioclase fractionation effects.
- Constraining the composition of primary TTG melts.
Main Results:
- TTG composition is influenced by amphibole and plagioclase fractionation.
- Primary TTG melts are incompatible element-poor with high La/Sm, Sm/Yb, Sr/Y, and positive Eu anomalies.
- Melting parameters indicate varying degrees of melting and fractional crystallization, not melting depth.
Conclusions:
- Archaean TTGs originated from the melting of rutile- and garnet-bearing plagioclase-cumulate rocks in proto-continental roots.
- This melting process links TTG magmatism to sanukitoid and K-rich granite formation.
- These processes explain Archaean continental crust growth and differentiation without external forcing.
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