Reply to Comment by Nutman et al. on “Tectonics of the Isua Supracrustal Belt I and II”

Structural and metamorphic analyses from the works under discussion (Ramírez-Salazar et al., 2021; Zuo et al., 2021a) show that the Isua supracrustal rocks can be interpreted to record one single deformation and metamorphic event featuring quasi-homogeneous deformation and amphibolite facies metamorphism, followed by late static retrogression or thermal event(s). Observed deformation and metamorphic records are consistent with three hypotheses: (1) they represent Neoarchean plate tectonic overprints following Eoarchean plate tectonic evolution (e.g., Nutman et al., in press); (2) they represent Eoarchean heat-pipe and/or plate tectonic deformation that survived later tectonic event(s) (e.g., Zuo et al., 2021a; Ramírez-Salazar et al., 2021), and; (3) they represent one major Neoarchean tectonic event, such that the Isua supracrustal belt (ISB) records Eoarchean protolith-related processes but does not record Eoarchean metamorphism nor deformation. While a heat-pipe model for crustal formation is central to hypothesis 2, it is also a viable crustal formation mechanism for hypothesis 3 where the ISB would still form in a heat-pipe setting in Eoarchean time, but the major deformation of the heat-pipe lithosphere happened during Neoarchean time, probably by (proto-)plate tectonic processes. If the data presented in Zuo et al. (2021a) and Ramírez-Salazar et al. (2021) only reflect Neoarchean histories, then these cannot be used to refute or support any Eoarchean geodynamic background for the formation of the ISB