Zircon Hf isotope evidence for a global transition between stagnant- and mobile-lid tectonics

The formation of the earliest continents is poorly understood—was plate tectonics operative or did other processes, such as stagnant-lid internal differentiation, dominate crustal production on the Hadean-Archean Earth? Geochemical and theoretical models suggest that early continents might have been generated by either modern-style, relatively rapid tectonic recycling of oceanic lithosphere or by reworking of long-lived mafic protocrust^1-3. To assess mechanisms of early continent formation and the geodynamic regime operative on the early Earth, we use a global compilation of hafnium isotope compositions preserved in 4.3-3.0 Ga zircons. These data indicate that crust formation before ~3.8 Ga occurred largely by internal, relatively closed-system reworking of long-lived mafic crust whereas, after ~3.8-3.6 Ga crust was produced by the widespread differentiation of relatively juvenile, mantle-derived magmas. We propose that this secular shift in the global hafnium isotope record reflects a widespread but progressive transition from stagnant- to mobile-lid tectonics on the early Earth.

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