The Evolution of the Continental Crust and the Onset of Plate Tectonics

Abstract

The Earth is the only known planet where plate tectonics is active, and different studies have concluded that plate tectonics commenced at times from the early Hadean to 700 Ma. Many arguments rely on proxies established on recent examples, such as paired metamorphic belts and magma geochemistry, and it can be difficult to establish the significance of such proxies in a hotter, older Earth. There is the question of scale, and how the results of different case studies are put in a wider global context. We explore approaches that indicate when plate tectonics became the dominant global regime, in part by evaluating when the effects of plate tectonics were established globally, rather than the first sign of its existence regionally. The geological record reflects when the continental crust became rigid enough to facilitate plate tectonics, through the onset of dyke swarms and large sedimentary basins, from relatively highpressure metamorphism and evidence for crustal thickening. Paired metamorphic belts are a feature of destructive plate margins over the last 700 Myr, but it is difficult to establish whether metamorphic events are associated spatially as well as temporally in older terrains. From 3.8 to 2.7 Ga, suites of high Th/Nb (subduction-related on the modern Earth) and low Th/Nb (non-subduction-related) magmas were generated at similar times in different locations, and there is a striking link between the geochemistry and the regional tectonic style. Archean cratons stabilized at different times in different areas from 3.1 to 2.5 Ga, and the composition of juvenile continental crust changed from mafic to more intermediate compositions. Xenon isotope data indicate that there was little recycling of volatiles before 3 Ga. Evidence for the juxtaposition of continental fragments back to ∼2.8 Ga, each with disparate histories highlights that fragments of crust were moving around laterally on the Earth. The reduction in crustal growth at ∼3 Ga is attributed to an increase in the rates at which differentiated continental crust was destroyed, and that coupled with the other changes at the end of the Archean are taken to reflect the onset of plate tectonics as the dominant global regime.

‘Whole Organism’, Systems Biology, and Top-Down Criteria for Evaluating Scenarios for the Origin of Life

“…Finally, we note that terrestrial scenarios face the possibility that while there was continental crust by at least 4 billion years ago [ 98 , 99 ] that the origin of emergent continental crust, that is terrestrial habitat, may have been as late as 3.5 billion years ago [ 98 , 100 ], but see [ 101 ], or even from 2.5 to 3 billion years ago [ 102 ]. However, others argue for terrestrial habitat much earlier [ 103 ]; similar to the study of the origin of life, understanding the early history of the Earth is also very difficult due to a lack of data, and there are still many points of disagreement [ 99 , 104 ].…”

“…Today the alkaline hydrothermal vents are found where mantle rock reaches sufficiently shallow depths for serpentinization to occur [ 143 ], including close to ultra-slow (<20 mm/year) to slow seafloor spreading ridges (20–50 mm/year), which constitute a significant proportion of the 60,000 km of mid-ocean ridges today [ 144 ]. In the Hadean it appears that plate tectonics as we know it may not have existed [ 98 , 104 , 145 , 146 ], and that there was a much greater exposure of mantle rock on the sea floor [ 147 , 148 ]. Today alkaline hydrothermal vents are one of the most geographically extensive of all proposed venues for the origin of life—in the Hadean they may have been vastly more numerous on a seafloor with its abundant Al-depleted komatiites [ 148 ].…”

Plombotectonique des gisements du Maroc

“…La genèse des gisements de plomb géants au Protérozoïque a été mise en relation avec l'intense mobilisation crustale lors de la formation du continent Nuna, la stabilisation de la lithosphère et l'ouverture de grands bassins au début du Mésoprotérozoïque (Sawkins, 1989 ;Hawkesworth et al, 2020). La construction continentale sur la marge nord du craton ouest-africain démarre un milliard d'années plus tard avec la formation du Gondwana, un continent à forte épaisseur crustale et largement émergent au-dessus du niveau de la mer (Traintafyllou et al, 2020).…”

Origin, Accretion, and Reworking of Continents

“…Over time, the development and continuous operation of plate tectonics are thought to have changed the way and rates of the growth, reworking, and destruction of continental crust compared with the pre-plate tectonics era (Dhuime et al, 2018;Hawkesworth et al, 2020). This is largely attributed to the widespread subduction and associated tectonic processes.…”