Ophiolitic trondhjemites: a possible analogue for Hadean felsic 'crust'

Abstract

AbstractIt has been argued that >4.0 Ga detrital zircons preserved in sediments of the Jack Hills, western Australia, preserve evidence for a well‐developed continental crust on the Earth at 4.4–4.5 Ga ago. Here, it is shown that there are geochemical similarities between the Jack Hills zircons and the zircons found in trondhjemites in ophiolite sequences, suggesting that the Earth's first felsic crust may have formed in a manner analogous to modern ophiolitic trondhjemites. The trondhjemites of the Oman ophiolite were formed by the hydrous partial melting of the upper (hornblende) gabbros in the roof‐zone of an axial magma chamber. A similar hydrous melting of a mafic protolith may have operated during the Hadean, to create small volumes of felsic rocks within a dominantly mafic crust, obviating the need to postulate a felsic continental crust at 4.4–4.5 Ga.