Thickening and felsification of Archaean crust stabilised the geotherm allowing for dyke swarms in the late Archaean

Dyke swarms and sedimentary basins tend to appear in the late Archaean (Cawood et al., 2022), suggesting that the crust was cold and brittle enough to facilitate and preserve dyke swarms. However, the thermal and mechanical state of the Archaean lithosphere that facilitates extensive diking and fracturing remains unclear. 

Continental crust seems to have been relatively mafic in the Archaean (Dhuime at el., 2015, Hawkesworth and Jaupart, 2021), but over less than one billion years, it underwent internal differentiation largely driven by in-situ radiogenic heat production (Perry et al., 2006, Michaut and Jaupart, 2007). Magmatic rocks in greenstone belts show bimodal silica distribution (Kamber, 2015), and bulk crust was composed of ~30% felsic crust and ~70% depleted or dehydrated mafic crust (Hawkesworth and Jaupart, 2021). Tonalite-trondhjemite-granodiorites (TTGs) are consistent with internal differentiation, and are thought to have been produced via partial melting of hydrous metabasalts (Moyen and Martin, 2012). A preferred model of the Archaean lithosphere is to generate mafic crust until it was thick enough to melt and form TTGs and then to have a more felsic crust that ultimately stabilised sufficiently for dyke swarms. 

Here, we test the hypothesis that thickening and internal differentiation (felsification) of Archaean crust led to major cooling of the lithosphere allowing dyke swarms to be a feature of the late Archaean. We calculate thermal profiles for the Archaean lithosphere for different scenarios of internal differentiation between 3.5−2.5 Ga that are consistent with present-day observations (e.g., Michaut and Jaupart, 2007). These thermal profiles are then used to investigate melt transport in the lithosphere using a two-phase flow model that incorporates a new poro-viscoelastic–viscoplastic theory with a free surface (Li et al., 2023, Pusok et al., 2025), designed and validated as a consistent means to model dykes. Results show that a warmer, weaker crust facilitates formation of sills and smaller dikes, while a cold, brittle crust facilitates formation of larger dykes. Our results suggest that dyke swarms are evidence for a cooling geotherm and strengthening of crust, and that crustal differentiation was a necessary condition for crustal stability of Archean provinces. This threshold for dyke swarm formation could have implications for the onset of widespread subduction and plate tectonics.

References

Cawood et al. (2022) Rev. Geophys. DOI:10.1029/2022RG000789

Dhuime at el. (2015), Nat. Geosci. DOI:10.1038/ngeo2466

Hawkesworth and Jaupart (2021), EPSL DOI:10.1016/j.epsl.2021.117091

Kamber (2015), Precam. Res. DOI:10.1016/j.precamres.2014.12.007

Li et al. (2023), GJI DOI:10.1093/gji/ggad173

Moyen and Martin (2012), Lithos DOI:10.1016/j.lithos.2012.06.010

Michaut and Jaupart (2007), EPSL DOI:10.1016/j.epsl.2007.02.019

Perry et al. (2006), JGR DOI:10.1029/2005JB003893

Pusok et al. (2025), GRL DOI:10.1029/2025GL115228