Modern oceanic crust is constantly produced at oceanic ridges and recycled back into the mantle at subduction zones via plate tectonics. An outstanding question in geology is whether the Earth started in a non-plate tectonic regime, and if it did, when the transition to the modern regime occurred. This is a complicated question to address because Archaean rocks lack modern equivalents to anchor interpretations. Here, we present a silicon isotopic study of 4.0–2.8-Gyr-old tonalite–trondhjemite–granodiorites, as well as Palaeozoic granites and modern adakites. We show that Archaean granitoids have heavier silicon isotopic compositions than granites and adakites, regardless of melting pressure. This is best explained if Archaean granitoids were formed by melting of subducted basaltic crust enriched in sedimentary silica through interaction with seawater.
This is part of the abstract of the paper published in Nature Geoscience by researchers at the Université de Paris, Institut de Physique du Globe de Paris, together with colleagues from the Université Clermont Auvergne, Laboratoire Magmas et Volcans, IRD, CNRS, UMR 6524, the Institut Universitaire de France, the University of Maryland and the University of Chicago.
Read the paper: An oceanic subduction origin for Archaean granitoids revealed by silicon isotopes. Zhengbin Deng et al. Nature Geoscience