Low δ18O and δ30Si TTG at ca. 2.3 Ga Hints at an Intraplate Rifting Onset of the Paleoproterozoic Supercontinent Cycle

Abstract

AbstractThe start of the Paleoproterozoic supercontinent cycle is typically taken as the initiation of orogenesis at ca. 2.1 Ga leading to the assembly of Earth's first supercontinent, Columbia. However, the dearth of ca. 2.5–2.2 Ga geological records makes it difficult to deduce tectonic factors during the onset of the Paleoproterozoic supercontinent cycle. The petrogenesis of tonalite–trondhjemite–granodiorite (TTG) provides useful proxies for tracing prevailing geodynamic regimes of early continental evolution. However, marked decreases of TTG and other magmatism occurred across the Archean–Paleoproterozoic transition and have previously precluded forming testable hypotheses. Early Paleoproterozoic TTGs have been identified in the North China Craton (NCC) and other cratons, which may represent the last major pulse of TTGs globally. Here we present low δ18O and δ30Si ca. 2.3 Ga TTGs from the NCC, together with thermodynamic modeling and compilation of stable O and Si isotopes for TTGs globally through time. The ca. 2.3 Ga TTGs were derived from the partial melting of Archean basaltic crust and give lighter average zircon δ18O (3.15 ± 0.35‰) and whole‐rock δ30Si values (−0.17 ± 0.08‰) than most Archean TTGs. Considering coeval mafic‐felsic igneous rocks, and lithospheric thinning since ca. 2.5 Ga based on estimated crustal thickness through the Neoarchean–Paleoproterozoic, we posit the onset of an intraplate rifting consistent with the anomalous low‐δ18O magmatism. Continental rifting of Archean cratons/supercratons plausibly hints at the formation of rifts driving subduction initiation as the veritable onset of the Paleoproterozoic supercontinent cycle.