Early Neoarchean Granitoid Diversification And Crust-mantle Geodynamic Regimes In The Jiaobei Terrane

The late Archean appearance of granitoid diversification globally represents one of the most remarkable features of changing geodynamics of our planetary Earth.Until now,the crust-mantle geodynamic origin of global late Archean granitoid diversification remains enigmatic.In this study,a series of early Neoarchean granitoid rocks were identified in the Jiaobei terrane of North China Craton,including²747-2734 Ma Na-rich quartz dioritic,tonalitic,and trondhjemitic?DTTG?gneisses and ²718-2701 Ma K-rich quartz monzodioritic,granodioritic,and monzogranitic gneisses.These rocks constitute a key early Neoarchean episode of granitoid diversification in the North China Craton.The quartz dioritic and TTG gneisses commonly show transitional field relationships,and they have low K₂O/Na₂O?0.19-0.59?and depleted zircon ?Hf?t₂?values?+1.3 to +6.9??They are characterized by decreasing MgO,FeO_T,TiO₂,P₂O₅,and CaO,increasing Eu anomalies?from negative to positive?and more fractionated REEs,with increasing SiO₂.Petrogenetic and geochemical modeling studies reveal that the quartz dioritic rocks could have been derived from the partial melting of a depleted mantle source metasomatized by slab-derived melts,whereas diverse TTG gneisses?classified into a low and a high silica group?formed by different degrees?⁵-15 % and 15-30 %?of fractionation from the quartz dioritic magmas,with inferred liquidus minerals of 89% hornblende + 5% clinopyroxene + 5% plagioclase +1% apatite.The K-rich granitoid gneisses show higher K₂O/Na₂O?0.67-2.87?but lower zircon ?Hf?t₂?values?-0.5 to +5.6?than those of DTTG gneisses,with some containing euhedral muscovites.The quartz monzodioritic and granodioritic gneisses have higher MgO and Mg^#,but lower Fe^*?FeO_T/?FeO_T+MgO??than the monzogranitic gneisses.It is suggested that these K-rich granitoids were generated by the partial melting of either a metasomatized mantle source with recycled sediments or metasedimentary rocks at diverse crustal levels.Based on the above petrogenetic discussions,the early Neoarchean crust-mantle interaction processes of Jiaobei terrane were reconstructed,including?1?earlier²747-2734 Ma slab-mantle wedge interactions under a continental marginal arc,forming quartz dioritic and the derivative tonalitic to trondhjemitic rocks;?2?ongoing convergence led to high relief of the arc mountain,facilitating erosion and reworking/recycling of sediments;and?3?different types of K-rich granitoids were generated by partial melting of coupled crust-mantle system during subsequent arc-continent accretion.It is further emphasized that the construction and erosion of thickened arcs have played critical roles triggering the late Archean granitoid diversification globally.