Partial melting of basaltic crust in the generation of Early Archean intrusive rocks: Insights from the near-zero Δ199Hg signature in Archean granitoids

Abstract Earth is unique in the solar system for hosting continental crust, whereas the mechanisms for the formation and evolution of continental crust remain controversial. Mercury (Hg) isotopes undergo mass-independent fractionation via photochemical reactions at Earth's surface, producing nonzero Δ199Hg values in the surface systems. Here, we conduct Hg analyses on Early Archean (3.6–3.0 Ga) granitic gneisses from the Anshan Complex. These rocks display overall near-zero Δ199Hg values (−0.13‰ to +0.08‰), overlapping estimates for the primitive mantle (−0.10‰ to +0.10‰), but contrasting with estimates for Phanerozoic arc-related granites (−0.3‰ to +0.2‰). This disparity in Δ199Hg supports two different genesis models for the continental crust. The nonzero Δ199Hg values of Phanerozoic granites suggest that the Phanerozoic continental crust was formed through mantle-crustal interactions driven by subduction of surface materials. The pervasive near-zero Δ199Hg signal in the Anshan granitoids over 600 m.y. is more consistent with a internally regulated vertical crustal evolution process than with a global subduction system that incorporate surface materials with variable Δ199Hg values.