Metamorphic constraints on Archean tectonics

The tectonic style of the Archean Earth is contentious, with ongoing debate concerning the dominant surface processes controlled by either a plate tectonics regime or alternative styles of tectonics (stagnant lid, heat pipe, drip tectonics, sluggish plates, and other planetary modes of heat loss). We assess the viability of interpretations of tectonics during the Archean using a newly compiled metamorphic database. A total of 142 metamorphic data points from Archean cratons have a majority of Neoarchean ages, followed by Paleoarchean, with few Eoarchean and Mesoarchean ages. This database is categorized into three groups of low, medium, and high metamorphic thermobaric ratio (T/P), with the inherent distributional characteristics pointing to subduction tectonics and non-subduction tectonics. We relate Archean cratons and continental history, crustal growth and reworking, and the horizontal motion of ancient cratons to infer which tectonic styles and processes operated. Our analysis is synthesized by the highlighting of three distinct Archean periods with different tectonic activity, starting at 3.8 billion years ago (Ga), from when the first metamorphic data are available. We find that in the interval 3.8–3.5 Ga, tectonics was dominated by short-lived subduction tectonics and non-subduction tectonics, possibly in cohabitation. Between 3.4 and 3.0 Ga, subduction was present and contributed to the lateral growth of the continents and emersion above sea level. In the 2.8–2.5 Ga period, the assembly of the supercontinent/supercratons signals the action of modern-style plate tectonics. In summary, Archean metamorphic data allow timing the Earth’s progression from pre-modern tectonics to modern plate tectonics including the supercontinent cycle.