Ultra-hot origins of stable continents

The origin and composition of Earth’s silica-rich continental crust, particularly the lower crust, remain uncertain. Stable continental crust, including cratons and crust older than 200 million years, is marked by enrichment of radiogenic heat-producing elements (U, Th and K) in the upper crust and depletion in the lower crust. Because the lower crust probably consists of >50% aluminous metasedimentary and evolved metaigneous rocks—both initially enriched in U and Th—continental differentiation requires a mechanism to transfer these elements upwards. Here, in our analysis of partially melted metasedimentary and metaigneous rocks, we show that ultrahigh temperatures (>900 °C) are essential to stratify heat production and stabilize crust. Removal of small fractions of ultrahigh-temperature melt generated by fluid-absent melting can produce the observed lower-crustal depletions in U and Th. By contrast, lower-temperature melting fails to drive differentiation owing to the resilience of monazite to dissolution in granitic melts. Our findings establish ultrahigh-temperature melting as an important criterion for the formation of stable continents, providing a direct link between the formation of cratons and ultrahigh-temperature metamorphic terrains and the supercontinent cycle. This insight constrains the tectonic settings responsible for crustal differentiation. Stabilization of continental crust requires temperatures of over 900 °C, establishing a link between ultrahigh-temperature metamorphism and craton formation, according to a study of U and Th concentrations in metasedimentary and metaigneous rocks.