Australia: The Land Where Time Began

A biography of the Australian continent 

Jack Hills Hadean Crust – Ophiolitic Trondhjemites - A Possible Analogue for Felsic ‘Crust’

It has been suggested that detrital zircons with an age of >4.0 Ga that have been preserved in sediments of the Jack Hills, Western Australia, preserved evidence for the presence of continental crust that was well-developed on Earth 4.4 – 4.5 Ga. In this paper Rollinson presents evidence that geochemical similarities between the zircons from Jack Hills and zircons found in trondhjemites in ophiolite sequences, suggesting that the first felsic crust on Earth may have formed in an analogous manner to that of modern trondhjemites. Hydrous partial melting of the upper (hornblende) gabbros in the roof-zone of an axial magma chamber resulted in the trondhjemites of the Oman ophiolite. Rollinson suggests a similar hydrous melting of a mafic protolith may have operated during the Hadean, forming small volumes of felsic rocks within a dominant mafic crust, which would obviate the need for postulating a felsic continental crust.

Sources & Further reading

1. Rollinson, H. (2008). "Ophiolitic trondhjemites: a possible analogue for Hadean felsic 'crust'." Terra Nova 20(5): 364-369.