Modern-style continental tectonics since the early Archean

We infer the nature of continental tectonics in the Precambrian by combining our understanding of the principles that govern the present-day behaviour of the continents, which over large parts of the Earth's surface does not resemble plate tectonics, with the available observations from the Precambrian rock record. We show that the hotter mantle potential temperature had little effect on continental rheology and behaviour. In contrast, higher rates of radiogenic heating played a key role in crustal melting and the subsequent rheological evolution of the continents, although feedbacks between heating, melting and dehydration would have resulted in Precambrian continental rheology and deformation rates similar to the present day. By at least the early Archean, and possibly earlier, deformation fabrics preserved in large swathes of crust and the pressure- temperature histories of metamorphic rocks imply mountain-building by shearing and thrust-stacking above rigid underthrusting foreland. This style of mountain-building requires the presence of rigid crustal blocks, which are the anhydrous residue of prior melt extraction following thickening of the crust and lithospheric mantle. The rheology of the forelands of mountain belts controls the crustal thickness contrasts that can be supported, and along with the rate of radiogenic heating that crustal thickness controls the temperatures attained. The interplay between decreasing radiogenic heating over Earth history and the development of strong crustal blocks that can support thick mountain ranges leads to optimal conditions for the generation of tonalite–trondhjemite–granodiorite (TTG) melts during hot Archean continental mountain building events, explaining both their Archean prevalence and subsequent decline. However, the overall style of continental tectonics has remained unchanged since at least the early Archean, and TTG petrogenesis simply represents this style of tectonics superimposed upon a higher rate of radiogenic heating. We suggest that this intrinsically modern-style deformation of the continents was preceded by a phase of (early?) Hadean tectonics resembling the deformation of skin on custard. Hydrous fault zones are too weak to form a 'stagnant lid' on Earth-like planets, and density-driven vertical motions (e.g. 'sagduction') occur at insignificant rates, further emphasising the uniformitarian nature of continental tectonics from the early Archean onwards.