Low δ18O zircon grains in the Neoarchean Rum Jungle Complex, northern Australia: An indicator of emergent continental crust

Oxygen isotope and trace element geochemistry of zircons from porphyry copper system: Implications for Late Triassic metallogenesis within the Yidun Terrane, southeastern Tibetan Plateau

“…S1), indicating that their nearidentical δ 18 O values are unlikely to have been reset by recrystallization or radiation damage, and that they have not diffusively exchanged oxygen with external melt or fluids along cracks (cf. Booth et al, 2005;Valley et al, 2005;Wan et al, 2013;Hollis et al, 2014). All of this indicates that magmatic δ 18 O values are retained within the zircons analyzed in this study.…”

Coupling of the atmosphere and sediment melts across the Archean-Proterozoic transition

“…The range and average δ 18 O values of sediment-melts increases post-2.3 Ga (Figure 3), in accord with previous studies that interpret the rise of average δ 18 O to be the result of continental emergence and a concomitant change in sediment composition 24,25 . Low δ 18 O values in sediment melts (equal or lower than the mantle value of 5.3 ± 0.6‰; 22 , like in 19GH9 and 19GH11B, are interpreted to re ect hydrothermal alteration of the protolith 37 . It has been proposed that interaction of a melt with hydrothermal meteoric water -a mechanism that requires emergent land area -may be the process responsible for such low δ 18 O melts 37 .…”

“…Low δ 18 O values in sediment melts (equal or lower than the mantle value of 5.3 ± 0.6‰; 22 , like in 19GH9 and 19GH11B, are interpreted to re ect hydrothermal alteration of the protolith 37 . It has been proposed that interaction of a melt with hydrothermal meteoric water -a mechanism that requires emergent land area -may be the process responsible for such low δ 18 O melts 37 . The emergence of continents at ~2.4 Ga is supported by changes to geochemical proxies at this time, such as an increase in seawater 87 Ga granitoids are small compared to those in pre-GOE sedimentary rocks (up to ~12‰) 14 , the magnitude of non-zero ∆ 33 S values observed here is too large to be the result of S-MDF processes alone ( Figure 2).…”

Emergence of continents above sea‐level influences sediment melt composition

“…Alternatively, increased δ 18 O of recycled material (Payne et al, 2015;Valley et al, 2005) could have driven the increase in zircon δ 18 O without requiring more efficient recycling. The ~2.35 Ga shift in average zircon δ 18 O coincides with the oxygenation of the Earth's atmosphere (Great Oxygenation Event; GOE) (Gumsley et al, 2017;Luo et al, 2016) and an increase in continental freeboard (the average elevation of continental crust above sea-level) (Flament et al, 2013;Hollis et al, 2014) that is proposed to have led to a shift in the triple-oxygen isotope composition of shales (Bindeman et al, 2018).…”