Diverse genesis of early Earth’s continental crust hints the geodynamic transition at about 3.0 Gyrs ago

Abstract

Tonalite-trondhjemite-granodiorite suites, dominating Earth’s early continental crust, likely formed by partial melting of hydrated metabasalt, but the specific conditions and mechanisms remain poorly constrained. Here, we conduct thermodynamic-geochemical modeling to systematically compare the roles that pressure, bulk H2O content, and source rock composition play in shaping these ancient rocks. Accordingly, we assess their optimal forming conditions, which are further validated by magmatic H2O contents retrieved from the apatite and zircon crystals of tonalite-trondhjemite-granodiorite suites. Our results highlight that pressure is the first-order factor controlling the formation and compositional diversity of these rock suites. Those with “high-pressure” geochemical characteristics are derived from fluid-fluxed melting at 14 – 16 kbar, a process readily explained by subduction rather than intraplate geodynamic regime. Furthermore, the temporal and spatial distributions of “high-pressure” variants, coupled with those of arc-like basalts, suggest subduction that likely initiated as a local phenomenon and transitioned to a global-scale process by 3.0 Ga.