Establishment of subduction at early Earth continent margins by migration: Implications for interpreting geochemical observations

Shifts in εHf values recorded in Hadean and Archean zircons and rare earth element (REE) patterns observed in the Acasta Gneiss Complex have been interpreted as reflecting felsic crust generation without subduction from ∼ 4.0 Ga, followed by the onset of subduction at 3.8-3.6 Ga. Subduction initiation may have been dynamically triggered by early continents at their margins, but the geodynamics of this process are unclear. Here, we use numerical mantle convection models to investigate the mechanisms and timescales for the development of subduction at continental margins on the early Earth. We identify two distinct subduction styles: “migrating intra-oceanic (transient) subduction” and “continent-anchored (persistent) subduction.”. We find continents do not dynamically trigger subduction at their margins. Instead, persistent subduction only develops after initial transient subduction zones collide with continental margins. Geochemical observations from the early Earth may instead reflect migration of existing subduction zones to continent margins. To test this hypothesis, we constrain the timescale over which persistent subduction develops in our models finding it ranges from 181–662 Myrs for Archean conditions, consistent with geological evidence from Hadean and Archean zircons. Our results suggest that the observed isotopic and geochemical shifts may be explained by the migration and stabilization of existing subduction zones at continental margins, rather than the initiation of subduction itself. This reframing highlights the central role of mantle dynamics in early Earth tectonics and calls for a reinterpretation of key geologic records previously attributed to the first onset of plate tectonics.