ORIGIN OF CONTINENTS: ISLAND ARC MODEL VS. OCEANIC PLATEAU MODEL
It is well known that all solid planets in the solar system have a core-mantle-crust structure, but a continental crust with a felsic composition is unique to the Earth. The Archean continental cratons consist mainly of orthogneisses and supracrustals that were metamorphosed from tonalite-trondhjemite-granodiorite (TTG) plutons and mafic-ultramafic volcanic rocks with minor sedimentary rocks, respectively. Available data suggest that these rock assemblages were derived from oceanic crust or its partial melts. The oceanic crust is generally divisible into ocean basin, mid-ocean ridge, island arc and oceanic plateau (ocean island), of which the ocean basin and mid-ocean ridge an average crustal thickness no more than 5-10 km, which is too thin to generate Archean TTG magmas. Therefore, continents with felsic composition must have been originated either from island arcs under a plate tectonic regime or from oceanic plateaus derived from mantle plume, which form two contrasting models for the origination of felsic continents. In this talk, I will present the pros and cons of evidence for the two models and also my own bias against the island arc model for the origin of Archean felsic continents.
Additional information: Prof. Guochun ZHAO, gzhao@hku.hk