Warm Subduction–Driven Formation of ∼2.7 Ga Tonalite-Trondhjemite-Granodiorite Gneiss in the Zhongtiao Mountains, Southern North China Craton: Constraints from Phase Equilibrium Modeling

Tonalite-trondhjemite-granodiorite (TTG) gneiss represents a significant portion of the Archean continental crust. Understanding the origin and compositional changes of TTG gneiss is crucial for unraveling the evolution of continental crust and the onset of global plate tectonics on Earth. The formation of Archean TTG gneiss has been attributed to partial melting of hydrous basalts, although the specific geodynamic setting remains uncertain. In this study, we focus on the ~2.7 Ga Sushui TTG gneiss from the Zhongtiao Mountains. To investigate the genesis of the Sushui TTG gneiss, we selected metabasites from the southern margin of the North China Craton (NCC) as the source rocks for quantitative forward modeling simulations of TTG magmas. Our findings show that the formation conditions of the ~2.7 Ga Sushui TTG gneiss in the Zhongtiao Mountains are consistent with a temperature gradient of 900°C/GPa and a 25%–30% degree of hydrous melting. The results indicate that the formation of the Sushui TTG gneiss occurred in a warm subduction environment, suggesting that plate tectonics might have been initiated through warm subduction mechanisms in the NCC at ~2.7 Ga.