DILEMMAS OF PLATE TECTONICS IN EXPLAINING THE NEOARCHEAN CRUSTAL FORMATION AND EVOLUTION OF THE EASTERN BLOCK, NORTH CHINA CRATON

Plate tectonics has successfully been applied to recognition of Paleoproterozoic orogenic belts in the North China Craton, but cannot well explain the following lithological, structural and metamorphic features that characterize the Neoarchean basement in the Eastern Block of the craton: (1) bimodal volcanic assemblages in the Neoarchean greenstones; (2) Neoarchean komatiites whose formation needed a melting process that occurred at 1600-1900°C; (3) nearly coeval emplacement of TTG rocks at 2.55-2.50 Ga, making up 80% of the total exposure of the Neoarchean basement; (4) mass balance problems if Archean TTG rocks were derived from the 10-30% partial melting of either eclogites or garnet amphibolites; (5) dominant domiform structures with vertical lineations; and (6) metamorphism characterized by anticlockwise P–T paths involving isobaric cooling following the peak metamorphism, which reflects the origin of the metamorphism related to underplating and intrusion of mantle-derived magmas. Although a continental magmatic arc model can also explain metamorphism involving anticlockwise P–T paths, it requires similar-aged relatively high pressure terrains with clockwise P-T paths to form paired metamorphic belts like those in current magmatic arcs. The lack of such relatively high pressure rocks metamorphosed at ~2.5 Ga in the Eastern Block makes plate tectonics as unfavorable model for the origin of the metamorphism in the Eastern Block of the North China Craton. This research was financially supported by a sub-project entitled “Growth and stabilization of continental crust and initialization of early plate tectonics of a NSFC Major Program “Continental crust evolution and Early plate tectonics” (41890831), and HKU Seed Fund for Basic Research (201811159089).