A Mesoarchean mantle plume-induced oceanic subduction in the Yangtze Craton, China: Evidence from tonalite−trondhjemite−granodiorites, sanukitoids, and metavolcanic rocks

The onset timing of plate tectonics and the main geodynamic mechanism responsible for subduction initiation are two crucial issues in current international Precambrian research. In this study, we identify two episodes of late Mesoarchean magmatic records (ca. 2.95 Ga and ca. 2.91−2.84 Ga) in the Kongling Complex of the Yangtze Craton, China. The first episode is dominated by ca. 2.95 Ga amphibolites that exhibit the chemical compositions characteristic of tholeiitic basalts. We infer that these rocks were generated by moderate-degrees of partial melting of spinel lherzolite from a depleted asthenospheric mantle source. The studied amphibolites, along with coeval komatiites/komatiitic basalts and tholeiitic basalts, were most likely formed in a rift setting associated with a mantle plume. The second episode mainly comprises ca. 2.91−2.90 Ga tonalite−trondhjemite−granodiorite (TTG) gneisses, ca. 2.88−2.87 Ga sanukitoids, and ca. 2.84 Ga TTG gneisses. We suggest that their parental magmas have complex origins, derived from the partial melting of a subducted oceanic slab (ca. 2.91−2.90 Ga TTGs), a fluids- and melts-metasomatized lithospheric mantle wedge (ca. 2.88−2.87 Ga sanukitoids), and a thickened mafic lower crust (ca. 2.84 Ga TTGs). The co-occurrence of slab-derived TTGs and sanukitoids therefore indicate a subduction setting during the late Mesoarchean. Combined with the presence of plume-related komatiites and tholeiitic basalts as well as subduction-related TTGs and sanukitoids in the Kongling Complex, we propose that a geodynamic transition from mantle plume to plate tectonic initially occurred at ca. 2.95−2.91 Ga in the northern Yangtze Craton. Similar tectonic evolution has also been recognized in many other Archean nuclei worldwide, such as the Sumozero-Kenozero, Wawa, Abitibi, and Bundelkhand greenstone belts, indicating that the upwelling of mantle plumes was one of the main geodynamic mechanisms responsible for the initiation of subduction on early Earth.