The late Archean-to-early Paleoproterozoic (~3-2 Ga) time witnessed major changes in the geological and geochemical makeup of the continental crust in response to the secular cooling of mantle and a concomitant change in the global geodynamics (Cawood et al., 2022). The latter includes the onset of horizontal movement of crustal blocks and the formation of local-scale tectonic cells involving convergent and divergent settings (cf. Gerya et al., 2015). However, whether or not these incipient convergent-divergent settings resemble modern subduction-collision and rift-zones, remains contentious. Recent numerical modelling shows that the style of lithospheric convergence may have evolved with the secular cooling of mantle since ~3 Ga (Chowdhury et al., 2017, 2020). In particular, the late Archean to early Paleoproterozoic lithospheres with thick and rheologically differentiated crust display evidence of large-scale delamination controlled orogenesis. Referred to as ‘peel-back orogenesis’ (Chowdhury et al., 2017, 2020), this tectonic process may have been triggered by the short-lived, late Archean subduction/downwelling events that occurred either spontaneously or due to plumes/impacts in the absence of a global mosaic of plates (cf. Sizova et al., 2015; Brown et al., 2020). The peel-back tectonic framework creates asymmetric tectono-thermal settings that can reconcile the secular changes in the ~3-2 Ga-old rock record including: (1) appearance of paired metamorphism; (2) slower cooling of high-grade metamorphic rocks; (3) dominant formation of MP-HP TTGs; and (3) formation of potassic granites and hybrid (high-MgO) granitoids. Thus, we propose that peel-back driven orogenic style dominated the late Archean-early Paleoproterozoic tectonics when the mantle was hotter. With the further cooling of mantle through the Proterozoic, its viscosity and lithospheric rigidity increased which allowed the isolated tectonic cells to evolve into a globally linked system of plates, i.e. plate tectonics (Cawood et al., 2022). However, the subduction zones and orogens possibly did not show modern, cold subduction or burial of continental crust to coesite forming depths on a global scale until late in the Proterozoic as the mantle was still warm enough to preclude these styles (Stern, 2018; Brown et al., 2020; Cawood et al., 2022). In fact, numerical models show that accretionary orogens may have experienced lithospheric peeling under early-to-mid Proterozoic mantle conditions (Chowdhury et al., 2017; Spencer et al., 2021).

Reference(s)

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Gerya, T.V. et al. 2015. Nature 527, 221–225. Sizova, E. et al. 2015. Precambrian Res. 271, 198–224.

Spencer, C.J. et al. 2021. Geophys. Res. Lett. 48, e2021GL093312.

Stern, R.J. 2018. Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 376, 20170406.