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Simultaneous generation of Archean crust and subcratonic roots by vertical tectonics

¹ Departments of Physics and Geology, University of Toronto, 60 St. George Street, Toronto, Ontario M5R1A7, Canada

Archean cratons are characterized by granite-greenstone belts, by abundant tonalites, trondhjemites, and granodiorites (TTGs), and by the presence of strong and buoyant subcratonic lithospheric mantle (SCLM). Individually, mechanisms for their formation remain controversial, and together they provide no clear picture of the tectonic style prevalent during the late Hadean and Early Archean. Following earlier observation that the dome-and-keel structure of granite-greenstone terranes resembles salt diapirs, we present numerical calculations that show that in pre-Archean to Middle Archean thermal regimes, mafic to ultramafic volcanics overlying a felsic basement will overturn diapirically in as few as 10 Ma, displacing as much as 60% of the volcanics to the lower crust. This suggests that diapirism may have dominated Hadean and Early Archean crustal tectonics. Furthermore, repeated cycles of bimodal volcanism and crustal recycling by diapirism provide a mechanism for making TTGs, leaving a restite that contributes to the SCLM from above. This diapiric tectonism later declined as the Earth cooled and plate tectonics became the dominant paradigm.