The ca. 3.8–3.6-b.y.-old Isua supracrustal belt of SW Greenland is Earth’s only site older than 3.2 Ga that is exclusively interpreted via plate-tectonic theory. The belt is divided into ca. 3.8 Ga and ca. 3.7 Ga halves, and these are interpreted as plate fragments that collided by ca. 3.6 Ga. However, such models are based on idiosyncratic interpretations of field observations and U-Pb zircon data, resulting in intricate, conflicting stratigraphic and structural interpretations. We reanalyzed published geochronological work and associated field constraints previously interpreted to show multiple plate-tectonic events and conducted field-based exploration of metamorphic and structural gradients previously interpreted to show heterogeneities recording plate-tectonic processes. Simpler interpretations are viable, i.e., the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ca. 3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. Integrating these findings, we present a new model in which two cycles of volcanic burial and resultant melting and tonalite-trondhjemite-granodiorite (TTG) intrusion produced first the ca. 3.8 Ga rocks and then the overlying ca. 3.7 Ga rocks, after which the whole belt was deformed and thinned in a shear zone, producing the multiscale a-type folding patterns. The Eoarchean assembly of the Isua supracrustal belt is therefore most simply explained by vertical stacking of volcanic and intrusive rocks followed by a single shearing event. In combination with well-preserved Paleoarchean terranes, these rocks record the waning downward advection of lithosphere inherent in volcanism-dominated heat-pipe tectonic models for early Earth. These interpretations are consistent with recent findings that early crust-mantle dynamics are remarkably similar across the solar system’s terrestrial bodies.

Models to describe the nature of the Earth's crustal evolution during the Archean vary substantially, from horizontal lithospheric motions with subduction-like movement (Abbott et al., 1994), to vertical tectonics defined by sub-/intralithospheric diapirism (Collins, 1989; Sizova et al., 2015), extensive volcanism (Moore & Webb, 2013; Turcotte, 1989), and the formation of a single-plate lithosphere. First-order questions include when and how horizontal lithospheric motion (e.g., subduction) became the dominant process by which Earth's interior cools, deforms, and evolves (Lenardic, 2018). A change in geodynamics between ∼3.2-2.5 Ga is proposed based on the global geochemical and zircon record indicating an increased contribution of reworked crust for magma generation while juvenile mantle additions decreased during that time (e.g., Dhuime et al., 2012; Moyen & Laurent, 2018). A recent review of the existing metamorphic record suggests that Earth has experienced spatial and temporal changes of global crustal thermal gradients probably linked to transitions in the tectonic regime, from stagnant-lid tectonics to mobile-lid plate tectonics (Brown & Johnson, 2018). The main changes occurred at ∼2.5 Ga, ∼1.0 Ga, and 0.72 Ga, Ga which are associated with the widespread appearance of paired metamorphic belts, dominance of high T/P gradients (>775°C/GPa), and increasing abundance of low T/P gradients (<375°C/GPa), respectively. The presence of a distinct bimodality of low and high T/P gradients is indeed a feature commonly associated with plate tectonics (Brown, 2010; Miyashiro, 1961, 1973) and its gradual emergence argues for progressive onset and evolution to horizontal-dominated geodynamics since the Neoarchean (Holder et al., 2019). In stark contrast with these interpretations, multiple subduction-driven events are invoked to explain the origin and evolution of the Eoarchean Isua supracrustal belt (ISB) of southwest Greenland (Figure 1), one of the oldest metamorphic terranes known, which some workers have interpreted to reflect the onset of plate tectonics as

Plate tectonic theory is the most renowned solid-Earth geoscience discovery of the 20th century, and yet there is no consensus hypothesis for how and why plate tectonics developed on Earth (e.g.

We thank A. P. Nutman, C. R. L. Friend, and V. C. Bennett for the opportunity to work alongside them in this Comment and Reply venue and beyond, to further develop new knowledge of this special terrane for understanding early Earth. Nutman et al. (2022) argue that in our prior works, particularly Ramírez-Salazar et al. (2021) andZuo et al. (2021), we have made errors and omissions, and thereby erroneously advanced a heat-pipe tectonic interpretation whilst missing diverse indicators of plate tectonics. Our published works argue for quasi-homogeneous amphibolite facies metamorphism and strain distribution across the Isua supracrustal belt (ISB) resulting from a single dominant Eoarchean event, whereas they interpret strongly heterogeneous Eoarchean metamorphism and deformation prior to a widespread Neoarchean tectonothermal overprint. In contrast, we suggest a model in which pre-deformation assembly of the main Isua lithologies was accomplished via magmatism and deposition in a heat-pipe cooling context, whereas Nutman et al. (2022) argue that the belt was assembled via Eoarchean plate tectonic collision as recorded by a suture preserved along the length of the belt. We emphasize at this point that the focus

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