Depth-dependent peridotite-melt interaction and the origin of variable silica in the cratonic mantle

• Published in: Nature communications 2021-02, Vol.12 (1), p.1082-1082, Article 1082
• Main Authors: Tomlinson, Emma L., Kamber, Balz S.
• Format: Article
• Language: English
• Subjects: 119/118; 704/2151/213/4114; 704/2151/431; Basalt; Cratons; Crystallization; Humanities and Social Sciences; Isotopes; Lithosphere; Magnesium; Melting; multidisciplinary; Olivine; Peridotite; Roots; Science; Science (multidisciplinary); Silica; Silicon dioxide; Thermodynamic models; Volcanic activity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-21343-9

Peridotites from the thick roots of Archaean cratons are known for their compositional diversity, whose origin remains debated. We report thermodynamic modelling results for reactions between peridotite and ascending mantle melts. Reaction between highly magnesian melt (komatiite) and peridotite leads to orthopyroxene crystallisation, yielding silica-rich harzburgite. By contrast, shallow basalt-peridotite reaction leads to olivine enrichment, producing magnesium-rich dunites that cannot be generated by simple melting. Komatiite is spatially and temporally associated with basalt within Archaean terranes indicating that modest-degree melting co-existed with advanced melting. We envisage a relatively cool mantle that experienced episodic hot upwellings, the two settings could have coexisted if roots of nascent cratons became locally strongly extended. Alternatively, deep refractory silica-rich residues could have been detached from shallower dunitic lithosphere prior to cratonic amalgamation. Regardless, the distinct Archaean melting-reaction environments collectively produced skewed and multi-modal olivine distributions in the cratonic lithosphere and bimodal mafic-ultramafic volcanism at surface. The compositional variability amongst Archaean cratonic peridotites has long been recognized, however its origin remains debated. The authors here find that the collapse of the dual Archaean mantle melting environment ceased production of silica-enriched mantle lithosphere.