Intense rift magmatism caused rapid thickening of Yilgarn Craton crust at 2.7 Ga

The crustal structure of many Archean cratons fits a paradigm of relatively thin crust (< 35 km), with felsic compositions, low-velocity lower crust and a sharp Moho discontinuity. This contrasts with the crusts of Proterozoic regions, which are typified by thicker crust (> 40 km), often with a high-velocity lower crust and a diffuse Moho. A global-scale transition in the nature of the crust is suggested, but its timing and nature remain unclear. The Yilgarn Craton in Western Australia has crustal thickness from ∼ 30 km to > 45 km and may preserve a key example of this transition. This study employs seismic-constrained gravity inversion to resolve in detail the thickness and density of the Yilgarn Craton crust. Regions with thick and dense crust are identified, and we explore two scenarios for their development: scenario 1 involves crustal shortening, erosion, and the development of a garnet-bearing lower crust, and scenario 2 involves addition of mafic magmatic rocks during extension. Scenario 2 is more consistent with the Neoarchean geology of the craton and the inferred extents of juvenile magmatism between 2.73 to 2.65 Ga. A regional stratigraphic unconformity at ca. 2.73 Ga is recognised as a turning point in the evolution of the craton, marking the crossing of thermo-rheological thresholds for geodynamically-stable lower crust. We suggest that net crustal thickening occurred over the next ∼40 Ma with a mafic magmatic input totalling 5.0 Mkm³ balanced by moderate extension (β-factor ∼ 1.1) Monte-Carlo simulations use a time-and-space distributed series of events of <40 Ma duration and <10 MKm³ vol to successfully explain modelled variations in global average crustal thickness through time. The event identified here aligns with a peak in constructive tendency, supporting the diachronous and episodic growth of the global lower crust during the Neoarchean.