What was Earth's tectonic style before Plate Tectonics?

Abstract:

In the Archean, deep mantle upwelling resulted in the formation of thick, buoyant, hot and therefore weak continental plates, as well as thicker oceanic crusts and plateaux that may have impeded and perhaps prevented modern style subduction. Continents were easy to deform and too weak to support high mountain belts and orogenic plateaux which characterize modern collisional orogens. Overall, it would be very surprising if Archean tectonics processes were similar than those observable today.

Over the past decade, numerical experiments have shown that the style of subduction depends on i/ the degree of coupling between the upper and lower plate which controls whether subduction zones are double sided or single sided; ii/ the buoyancy of the subducting plate which controls whether subduction is spontaneous or requires a push and whether slabs retreat or not; iii/ the yield stress of the subducting plate which controls whether recurrent slab breakoff occurs or not.

Studies focused on the behaviour of continental plates show that only minor thickening (tectonic or volcanic via the emplacement of continental flood basalts) is required for the crust to reach its solidus, which would have promoted the foundering of greenstone covers into the crust (sagduction).

In a convergence setting, weak continents would have deformed easily and convergence mainly accommodated by lateral expulsion and lateral flow under a regional transcurrent tectonic regime.

Numerical experiments suggest that thick and buoyant continents would have imparted significant horizontal stresses on adjacent oceanic plates, the slow spreading of thick and buoyant continents leading to the initiation of subduction.

Provided that continental lithospheric mantle could spontaneously subduct, numerical experiments suggest that in a convergent setting accretionary orogeny rather than continental collision was a dominant tectonic style with implications for crustal growth and differentiation.