Archean to Early Proterozoic tectonics and crustal evolution: a review

Abstract

Hypothesis on the formation and evolution of the Earth's continental crust in the Early Precambrian have to account for the independent and directionally consistent motion of crustal segments of considerable dimensions since at least 3,5 Ga ago, and at minimum velocities comparable to those of today. It seems established, therefore, that plate tectonics has governed lithospheric evolution since the generation of rigid crustal segmenta, and it is speculated that a change in style of plate interaction, rather than a change in fundamental mechanisms, has determined non-uniformitarian crustal evolution towards the present Wilson cycle. Uncertainties in the reliable reconstruction of Archaean tectonic settings are caused by low-temperature rock alteration that may obliterate primary magma tic trends, by the variable possible sources and melting processes for the generation of bimodal and calc-alkaline associations, and by disagreement on the interpretation of rocks with primitive isotopic characteristics. It is suggested that magmatic underplating played a major role in lithospheric growth and that reworking of continental crust during large-scale crustal differentiation was more important in the Archaean than recognized by most currently popular models. The generation and survival of first continental crust is seen in analogy with the evolution of Iceland, and later greenstone belt development was probably largely intracontinental, following a rift-and-sag mede in response to crustal rearrangements. Most high-grade terrains are considered to be older than neighbouring or overlying greenstone associations and were brought to the surface through low-angle thrusting. Archaean lithospheric growth built stable cratons that experienced little internal deformation in early Proterozoic times. Less stabilized crust reacts to large-scale distortions predominantly by stretching, elongate basin-formation and ensialic orogeny through mechanisms ranging from crust restacking to transform shearing, finally generating mobile belts. Locally, modern-type convergent plate margins become recognizable at about 2.2 Ga ago while the full Wilson cycle is finally established in the late Proterozoic.