Seminar

Plate tectonics has successfully been applied to Proterozoic and Phanerozoic geology, but cannot well explain the following lithological, structural and metamorphic features that characterize the Neoarchean continental blocks: (1) dominant bimodal volcanic assemblages in the Archean greenstones; (2) Archean komatiites whose formation needed a melting process that occurred at 1600-1900°C; (3) nearly coeval emplacement of TTG rocks making up 60-70% of Archean terranes; (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 in Archean terranes makes plate tectonics as unfavorable model. In contrast, we favor models involving vertical tectonics like mantle plume or sugduction models for the formation and evolution of Archean crust.