Silicified seafloor contribution to TTG formation: insights from zircon O and Si isotopes

Tracing the input of altered seafloor lithologies to primary melts of tonalite-trondhjemite-granodiorite suites (TTGs) is critical for understanding Archean geodynamic processes that transported these lithologies towards melting regions. Zircon oxygen and silicon isotopic compositions in TTGs are particularly useful for this end, but their interpretation remains challenged by scarce quantitative constrains on isotopic compositions reflecting partial melting of specific Archean lithologies. Here, we combine oxygen and silicon isotope measurements in 3.45 and 3.22 Ga Barberton TTGs and their zircons with numerical models simulating partial melting of different source lithologies, which predict the isotope signatures of zircons and their host melts. Measured whole rock and zircon O and Si isotope compositions reflect the presence of up to 30 wt. % of hydrothermally silicified mafic rocks derived from the seafloor in the Barberton TTG source region. Considering the regional geological context, we propose subduction-like processes to explain the burial of the silicified seafloor into the TTG source. These results imply that subduction-like processes operated at least locally on Earth during the Paleoarchean.