Mesoproterozoic tectonic environment in the ‘Boring Billion’: Insight from the Algoma-type BIF along the central–western Korean Peninsula

The middle age of the Earth termed as the ‘Boring Billion’ (ca. 1.8–0.8 Ga), is characterized by prolonged tectonic quiescence, low atmospheric oxygen, and globally anoxic ocean conditions. Relatively limited tectonic activity during this period poses challenges for paleogeographic reconstructions of continental configurations. We present newly discovered banded-iron formation (BIF)-bearing metamorphosed (volcano-)sedimentary succession in the Seosan area of the central–western Korean Peninsula, providing crucial clues on the Mesoproterozoic tectonic environment. It consists, from NE to SW (oceanward to inland), of quartzite, amphibolite-calc-silicate gneiss, calc-silicate marble, BIF-bearing quartzite, quartzite, and biotite-muscovite schist. Association of hydrothermally precipitated quartz-bearing amphibolite-calc-silicate gneiss and calc-silicate marble, together with BIF indicate precipitation of Fe-oxides from hydrothermal fluids. Geochemical characteristics of the BIF, including chondritic Y/Ho ratios (∼28), suggest Algoma-type origin, while the presence of quartzite and biotite-muscovite schist reflect silici-clastic sedimentation. Amphibolite within amphibolite-calc-silicate gneiss shows sub-alkaline basaltic composition, indicating a mafic source. Trace and rare earth element patterns match with ocean island basalt (OIB) and enriched mid-ocean ridge basalt (E-MORB), implying continental rifting analogous to modern Iceland plume-ridge interaction. U-Pb dating of amphibolite zircon yields ca. 1419 Ma, representing the timing of rifting, while metamorphism occurred at ca. 251 Ma. U-Pb zircon ages from BIF-bearing quartzite indicate Archean–Paleoproterozoic provenance (ca. 2496–1810 Ma). Our findings suggest that the earliest Mesoproterozoic rifting and sedimentation in the central-western Korean Peninsula correlate with rift systems of the North China Craton (e.g., Bayan Obo, Yanliao, Xionger), as part of global rifting associated with the breakup of Columbia supercontinent. Subsequently, the rift-related successions were buried to ∼4–5 kbar and 350–400 °C (12–15 km), and metamorphosed to amphibolite facies during successive Permo-Triassic subduction-collision events, leading to amalgamation of the North China Craton with microcontinent(s) derived from it.