Abstract The geodynamic regime of the early Earth remains elusive, with so far proposed hypotheses ranging from stagnant lid convection to rapid plate tectonics. Available geological data are severely limited for the first two billion years of the Earth's history, and this scarcity of relevant data is often compounded by the nonuniqueness of interpretation. Here we propose that the samarium–neodymium isotope evolution, which has been suggested to be consistent with stagnant lid convection in the early Earth, may be better understood as the result of rapid crustal growth and extensive crustal recycling. We delineate the permissible scenario of crustal evolution through geochemical box modeling with a Monte Carlo sampling of the model parameter space, and our results suggest that the net growth of continental crust was complete by the end of the Hadean and that the rate of crustal recycling could have been as high as 2 − 4 × 10 22 kg Gyr−1 at that time and has gradually decreased since then. Such crustal evolution yields a specific prediction for the present-day distribution of crustal formation ages, which is shown to be in remarkable agreement with a recent estimate based on the global compilation of zircon age data. The mode of subsolidus mantle convection after the putative magma ocean is probably plate tectonics, but its style could have been very different from that of contemporary plate tectonics, characterized by more voluminous magmatism and more destructive subduction.
The Au–Ag epithermal mineralization of the Shila Cordillera is dated at about 10.7 Ma (K/Ar on adularia). The vein system is characterized by the association of a major ≈east–west vein and N120–135°E secondary fractures. The strike-slip faults controlling the veins indicate an initial NE–SW to ENE–WSW shortening direction, which is compatible with that generally accepted for this period. These structures were reopened during a second phase and channelized mineralizing fluids, the circulation of which may have began at the end of stage 1. Les minéralisations épithermales à Au–Ag de la Cordillera Shila sont datées à environ 10,7 Ma (K/Ar sur adulaire). Le système de veines est caractérisé par l'association entre une veine principale sensiblement est–ouest et des fractures satellites N120 à N135°E. Les décrochements contrôlant les veines indiquent une direction de raccourcissement initiale NE–SW à ENE–WSW, compatible avec celle généralement admise pour cette période. Dans un deuxième stade, ces structures sont ré-ouvertes pour servir de réceptacle aux fluides minéralisateurs, dont la circulation débute probablement dès la fin du stade 1.
