The Granulite Facies, Partial Melting and the Archaean Crust

摘要: As chairman of a session the meeting I would like to add few comments concerning some problems discussed. During discussions certain important conclusions have appeared. The detailed descriptions presented oldest known samples Earth indicate that at time crust had already remarkably similar structure and chemistry more modern times. It has also been made clear rocks granulite facies make massive contribution base ancient logically could large regions under batholith zones mobile belts, where thickened by tectonic events. seems possible mantle processes controlling tectonics in Archaean, while having features common with present regime, were unique. Most models Earth's thermal history (Birch i965) suggest very hot initial stage it is difficult see how general geochemical equilibrium state be achieved without degree melting period history. If molten fraction assumed, preclude complex convective structures. Crust will appear when surface temperatures approach 800 ?C whichl early indeed. When liquid water appears on 100 or less, kilometres thick rapidly form. Some (Finale I97I) formation hydrosphere might an event this process itself accelerate cooling. well expected earliest semi-stable crustal fragments granitic. Such materials capable floating basalt liquids solid engulfed. This concentrate radioactive species (see Heier, volume). aqueous phase present, weathering intense partly account supply acids from volcanism ancd glassy volcanic debris. Early separation associated thus synchronous thicker formation. initially gradients order km-' hardly than 10 km before belting occur occurrence igneous overturn material. now abundantly appearance simple life forms 'were separated brief so bio-geochemical precipitates separations operate primitive stage.