Paleoenvironmental constraints of iron formation in the Fushun Area, northern Liaoning: insights from petrography, geochemistry, and isotope analysis

Iron Formations (IFs) are critical records for reconstructing the surface environment and geochemical evolution of early Earth. As economically significant Precambrian sedimentary rocks, they serve as key archives for reconstructing early Earth’s tectonic settings and paleoenvironmental conditions. This study focuses on a unique silicate IF at Nianpan (NP), Fushun area, northern Liaoning Province, which differs from typical Banded Iron Formations (BIFs) in its distinctive mineral assemblage. By integrating petrographic, mineral-chemical, geochemical, geochronological, and isotopic analyses, we reconstruct the protolith composition and depositional environment of this specific type of IF. The NP IF comprises two main rock types: magnetite-bearing two-pyroxene ore and banded ferrosilicate quartzite, both exhibiting a well-developed compositional banding. Thermobarometric calculations using the two-pyroxene thermometer and the garnet-orthopyroxene barometer constrain peak metamorphic conditions to granulite-facies (815 °C/1.05 GPa). Zircon U-Pb dating yields a depositional age of 2533.0 ± 6.8 Ma and a metamorphic age of 2485.7 ± 7.8 Ma. Systematic geochemical and isotopic analyses demonstrate that the protolith sediments were primarily derived from seawater, with a minor hydrothermal contribution (