Neoarchean high-pressure metamorphic record in the 1.9 Ga Belomorian eclogite: implication for plate tectonics onset

Abstract The timing of plate tectonics onset is still debated. It may have developed gradually since the Archean, evolving from warm (ancient) to cold (modern) regimes. However, there is still a lack of robust petrologic evidence, such as Archean subduction products like eclogite, and it is unclear when and how such a tectonic mode transition occurred. Here we examine the well-preserved Belomorian eclogites from Fennoscandia, in which we identify two high-pressure metamorphic events in the Neoarchean (2.72-2.70 Ga) and Paleoproterozoic (1.92-1.84 Ga). The Neoarchean event is inferred from the omphacite-associated inclusions within the metamorphic zircon cores, reflecting likely warm tectonic conditions (333-425 °C/GPa). The Paleoproterozoic metamorphism, recorded by zircon rims, represents eclogite facies. The petrologic-mineralogical data of these eclogites indicate cold subduction conditions (300 ± 12 °C/GPa) consistent with our previous conclusions. Each event has global counterparts, marking ancient and modern style plate tectonics. In summary, the Belomorian eclogite records the transition in plate tectonics from ancient (warm) to modern (cold) styles through two episodes of HP metamorphism.