What drove the delayed breakup of Nuna during Earth’s Middle Age?

Earth’s Middle Age (1.8-0.8 Ga) witnessed prolonged stability of the Nuna supercontinent, yet its breakup history remains enigmatic. We analyse the spatiotemporal evolution of arc and anorogenic magmatism, sedimentary deposition, and large igneous provinces (LIPs) emplacement during this period. Our results reveal that retreating accretionary orogens and back-arc extension occurred along the Laurentia-Baltic margins of Nuna from around 1.8 Ga to 1.5 Ga. The retreating mode was likely linked to elevated mantle temperatures, which, as supported by numerical models, enhanced rapid slab rollback and formation of wide back-arc basins. Importantly, LIPs during this interval were predominantly confined to Nuna’s margins, while widespread intracontinental plumes only emerged at 1.4-1.3 Ga. We propose that Nuna’s breakup was delayed until this time because earlier subduction delivered cold, dense oceanic lithosphere to the core-mantle boundary, inhibiting the rise of hot mantle plumes beneath the supercontinent. Only after this material was sufficiently heated could buoyant, hot mantle plumes rise beneath the continental blocks and drive fragmentation. This protracted stability maintained a warm upper mantle status, which weakened the continental lithosphere and reduced surface erosion, linking deep geodynamic processes to the environmental stasis of the ‘Boring Billion’.