Tectonic switch from a lithospheric rift to an active continental margin in the Paleoproterozoic: Evidence from low δ18O granites from the Trans-North China Orogen in the North China Craton

•The 2.31 Ga Low δ18O granites were related to partial melting of high-T hydrothermal altered crustal rocks in a rift.•The weaker low-18O signatures of the 2.18 Ga granites were inherited from the 2.31 Ga granites.•The southern TNCO went through tectonic switch from continental rift to active continental margin during 2.3–2.1 Ga.