Early hydrosphere-rock interactions and intra-crustal recycling recorded by remarkably high-δ18O Mesoarchean granitoids in the Sulu orogenic belt, eastern China

Abstract

When, why and how global plate tectonics were initiated, as well as secular changes of plate tectonics over time are fundamental issues in the earth sciences. In this study, we present a combined U-Pb, Hf and O isotope dataset for complex zircons from the high-grade granitic (TTG) gneisses of the Haiyangsuo complex in the Sulu orogenic belt, eastern China. This combined dataset reveals that the granitoids formed by at least ca. 3.22, 2.81, 2.70 and 2.58 Ga and recorded multiple metamorphic thermal events that occurred at ca. 3.05, 2.60–2.50 and 1.93–1.85 Ga. The 3.22 and 2.58 Ga granitoids have negative εHf(t) values (averages of −2.08 and −10.81, respectively) and were derived from remelting of evolved Eoarchean crust, in combination of 3.47 Ga inherited zircon, reflecting occurrence of matured felsic continent crust in the Paleoarchean, whereas the 2.81 and 2.70 Ga granitoids show positive εHf(t) values (averages of + 4.32 and + 2.23, respectively) and formed by remelting of juvenile crust derived from depleted mantle at ca. 3.0 Ga. The 3.22, 2.70 and 2.58 Ga granitoids have mantle-like or slightly enriched zircon δ18O values (averages of 5.53 ± 0.15, 5.41 ± 0.18 and 6.10 ± 0.22‰, respectively). However, the 2.81 Ga granitoid displays remarkably high zircon δ18O values ranging from 9.65 to 7.02‰ with an average of 8.48 ± 0.29‰ (1 SD), this demonstrates occurrences of early hydrosphere-rock interactions and intra-crustal recycling in the Mesoarchean. Synthetically, here we propose the following tectonic model for the formation of the high-δ18O Mesoarchean granitoids: (1) Generation of voluminous high-density lower crust along with the formation of early felsic continent dominated by TTGs; (2) gravity-driven subduction of denser oceanic crust relative to continental crust induced by delamination of high-density lower crust together with lithospheric mantle; and (3) subsequently partial melting of altered high-δ18O hydrated oceanic crust caused by delamination-induced hot asthenospheric mantle upwelling to form the high-δ18O Mesoarchean granitoid. Furthermore, we argue that gravity-driven subduction occurred in the Archean, and subduction may be responsible for the trend towards increasing δ18O values within zircons since the Mesoarchean.