Formation of early Archean Granite-Greenstone Terranes from a globally chondritic mantle: Insights from igneous rocks of the Pilbara Craton, Western Australia

Crustal rejuvenation stabilised Earth’s first cratons

“…3c, ref. 17 ). However, the spread from suprachondritic (positive εHf (t) ) to less radiogenic (negative εHf (t) ) endmembers implies that these TTGs were not purely juvenile additions to the crust, but were emplaced within, and extensively reworked their Hadean crustal substrates 24 .…”

“…However, the extraction of isotopically juvenile precursors to zircon-bearing magmas is not unique to convergent margin settings. Early Archaean plateau-type terranes, such as the archetypal East Pilbara Terrane 12 , 36 , are inferred to have formed in a poorly mobile lid setting above long-lived mantle upwellings 37 , 38 , which presents an equally viable geodynamic setting for the production of evolved magmas with juvenile zircon-Hf isotopic compositions 17 , 39 . Although zircon-Hf isotope data alone is not diagnostic of the specific geodynamic processes operating in early Archaean, the key advance made by this study is to highlight that the distinct change in the geodynamic setting of crust formation across Hadean–Archaean transition was coincident with the stabilisation of the first cratons.…”

“…The 176 Lu- 176 Hf decay system is well-suited to characterising the source of TTGs, as the fractionation of Lu from Hf during partial melting results in the mantle (high 176 Lu/ 177 Hf) and crust (low 176 Lu/ 177 Hf) developing distinct time-integrated radiogenic Hf isotopic compositions. Consequently, Eoarchaean TTGs sourced from juvenile reservoirs inherited the near-chondritic Hf isotopic composition of the Eoarchaean mantle 16 , 17 , whereas Eoarchaean TTGs sourced from ancient reservoirs acquired less radiogenic (sub-chondritic) Hf isotopic signatures. Zircon is an ideal tool to study the Hf isotopic character of ancient TTGs as it is a ubiquitous phase in evolved magmas and preserves the Hf isotope signature of its parental melt owing to its low Lu/Hf (<0.001) and resilience to isotopic resetting.…”

Insight into Archean crustal growth and mantle evolution from multi-isotope U-Pb and Lu-Hf analysis of detrital zircon grains from the Abitibi and Pontiac subprovinces, Canada

“…The earliest evidence for Hadean to Eoarchean crust from the zircon record suggests derivation from a primitive, chondritic uniform reservoir (CHUR; Amelin et al, 1999;Kemp et al, 2010;Guitreau et al, 2012;Hiess and Bennett, 2016;Vezinet et al, 2018). In addition, the predominance of CHUR compositions in early-Earth zircon has been used, in part, to support the interpretation that Hadean to early Archean crustal growth occurred by derivation from a primitive mantle in plume-dominated regimes with little to no influence of older enriched crust or a coeval depleted mantle reservoir (Bédard, 2018;Fisher and Vervoort, 2018;Petersson et al, 2020). Where local signatures indicative of crustal differentiation from a depleted mantle (DM) reservoir are observed, the possible occurrence of nascent subduction has been invoked (Hoffmann et al, 2010).…”

“…In Proterozoic and younger settings, it is well established that the evolution of crust and mantle reservoirs is predominately moderated by plate tectonic processes where geochemically differentiated crust and depleted mantle are complementary (Hofmann, 1988). While the operation of plate tectonic processes in the Archean is uncertain (Smithies et al, 2005;Piper, 2013;Bédard and Harris, 2014;Bédard, 2018;Petersson et al, 2020), it has been proposed that subduction may have been transient (Moyen and van Hunen, 2012), producing isolated mantle domains with DM-like signatures. Alternatively, Archean geodynamic processes may have included more sustained plate tectonics with long-lived subduction (Shirey et al, 2008) that produced a regional to globally extensive depleted mantle reservoir.…”