Generation of Earth’s Early Continents From a Relatively Cool Archean Mantle

Abstract

Several lines of evidence suggest that the Archean (4.0–2.5 Ga) mantle was hotter than today’s potential temperature(TP ) of 1350 ýC. However, the magnitude of such di erence is poorly constrained, with TP estimation spanningfrom 1500 ýC to 1600 ýC during the Meso-Archean (3.2-2.8 Ga). Such di erences have major implications for theinterpreted mechanisms of continental crust generation on the early Earth, as their e cacy is highly sensitive to theTP . Here, we integrate petrological modeling with thermo-mechanical simulations to understand the dynamics ofcrust formation during Archean. Our results predict that partial melting of primitive oceanic crust produces felsicmelts with geochemical signatures matching those observed in Archean cratons from a mantle TP as low as 1450ýC thanks to lithospheric-scale Rayleigh–Taylor-type instabilities. These simulations also infer the occurrence ofintraplate deformation events that allow an e cient transport of crustal material into the mantle, hydrating it.

Rapid ductile strain localization due to thermal runaway

“…Up to and including η reg = 10 15 Pa s, we observe no significant changes in the stress evolution of the models (Figure 4a). While this value is large in the context of our study, it is still well below the lower viscosity cut-off of geodynamic models which is commonly 10 18 Pa s or even higher (e.g., Thielmann & Kaus, 2012;Piccolo et al, 2019;Glerum et al, 2018). This implies that thermal runaway with temperature and velocity spikes, as described in section 3.1, is unlikely to be observable in large scale geodynamic models.…”