Could Iceland be a modern analogue for the Earth's early continental crust?

Abstract

For the last two decades, Iceland and other oceanic plateaux have been considered as potential analogues for the formation of the early Earth's continental crust. This study examines the compositions of silicic rocks from modern oceanic plateaux, revealing their differences to Archaean continental rock types (trondhjemite-tonalite-granodiorite or TTG) and thereby emphasising the contrasted mechanisms and/or sources for their respective origins. In most oceanic plateaux, felsic magmas are thought to be formed by fractional crystallization of basalts. In Iceland, the interaction between mantle plume and the Mid-Atlantic ridge results in an abnormally high geothermal gradient and melting of the hydrated metabasaltic crust. However, despite the current 'Archaean-like' high geothermal gradients, melting takes place at a shallow depth and is unable to reproduce the TTG trace element signature. Consequently, oceanic plateaux are not suitable environments for the genesis of the Archaean continental crust. However, their subduction could account for the episodic crustal growth which has occurred throughout the Earth's history. © 2008 Blackwell Publishing.