Melting experiments and the origins of felsic crust on early Earth

Abstract

Understanding the origin of Earth's earliest felsic crust has been a fundamental question in geology since the foundational insights of James Hutton and the pioneering high-temperature melting experiments of James Hall. Building on this historical framework, this study synthesises three decades of modern experimental petrology to reassess the processes responsible for generating tonalite-trondhjemite-granodiorite (TTG) suite rocks, the dominant components of early continental crust. Integrating high-pressure melting experiments highlights the influence of starting composition, water content, oxygen fugacity, and pressure-temperature conditions on melt products. Dehydration melting of hydrated metabasalt is shown to reliably produce TTG-like liquids, although stabilisation of garnet and rutile - and thus reproduction of high-pressure TTG trace-element signatures - requires realistic early Earth redox conditions and pressures ≥14–18 kbar, consistent with deep crustal or subduction-like environments. Lower-pressure TTG can be generated in intracrustal settings, implying the operation of multiple geodynamic processes on early Earth.