Temporal evolution of the early−late Neoarchean granitoid magmatism in the eastern North China Craton: Transition of geodynamic regime from mantle plume to continental marginal arc system

Abstract

A study of tonalite−trondhjemite−granodiorite (TTG) suite and sanukitoids emplaced at different ages in the Archean can constrain the transition of early Earth’s tectonic regime, which remains a subject of debate. In this contribution, we report a systematic investigation of an early Neoarchean and late Neoarchean TTG-sanukitoid association from the eastern North China Craton based on mineralogical, petrological, and geochemical evidence. The geochemical features of the 2.7 Ga TTG rocks studied suggest that their magma was primarily generated by partial melting of garnet-amphibolite and eclogite. Moreover, they are characterized by relatively low values of MgO, Mg#, Cr, and Ni, and zircon ɛHf(t) that varies mostly with evolved signature, which suggests that the primary magma of the TTGs was generated in a setting of thickened lower crust. The 2.5 Ga high-K calc-alkaline granitoids studied show an affinity to Archean sanukitoids. Their representative major and trace elemental and isotopic features suggest that they were derived from partial melting of mantle wedge metasomatized by subducted fluids and slab- and sediment-derived melts, followed by varying degrees of mineral fractional crystallization. The eastern North China Craton may have developed a continental marginal arc system in the late Neoarchean attached to another craton in the global Kenorland supercontinent, which might have eventually resulted in its final cratonization. The distinct tectonic settings of the two types of granitoids may indicate a transition of the tectonic regime from vertical in the early Neoarchean to horizontal at the end of the late Neoarchean. Moreover, the low δ18O values found in this study as well as those in other areas of the globe suggest that they were probably related to cold climatic conditions and/or elevated latitudes or altitudes.