Zircon age peaks at 2100-1650 and 1200-1000 Ma correlate with craton collisions in the growth of supercontinents Nuna and Rodinia, respectively, with a time interval between collisions mostly <50 Myr (range 0-250 Myr). Collisional orogens are two types: those with subduction durations <500 Myr and those ≥500 Myr. The latter group comprises orogens with long-lived accretionary stages between Nuna and Rodinia assemblies. Neither orogen age nor duration of either subduction or collision correlates with the volume of orogen preserved. Most rocks preserved date to the pre-collisional, subduction (ocean-basin closing) stage and not to the collisional stage. The most widely preserved tectonic setting in Proterozoic orogens is the continental arc (10%-90%, mean 60%), with oceanic tectonic settings (oceanic crust, arcs, islands and plateaus, serpentinites, pelagic sediments) comprising <20% and mostly <10%. Reworked components comprise 20%-80% (mean 32%) and microcratons comprise a minor but poorly known fraction. Nd and Hf isotopic data indicate that Proterozoic orogens contain from 10% to 60% of juvenile crust (mean 36%) and 40%-75% reworked crust (mean 64%). Neither the fraction nor the rate of preservation of juvenile crust is related to the collision age nor to the duration of subduction. Regardless of the duration of subduction, the amount of juvenile crust preserved reaches a maximum of about 60%, and 37% of the volume of juvenile continental crust preserved between 2000 and 1000 Ma was produced in the Great Proterozoic Accretionary Orogen (GPAO). Pronounced minima occur in frequency of zircon ages of rocks preserved in the GPAO; with minima at 1600-1500 Ma in Laurentia; 1700-1600 Ma in Amazonia; and 1750-1700 Ma in Baltica. If these minima are due to subduction erosion and delamination as in the Andes in the last 250 Myr; approximately one third of the volume of the Laurentian part of the GPAO could have been recycled into the mantle between 1500 and 1250 Ma. This may have enriched the mantle wedge in incompatible elements and water leading to the production of felsic magmas responsible for the widespread granite-rhyolite province of this age. A rapid decrease in global Nd and in detrital zircon Hf model ages between about 1600 and 1250 Ma could reflect an increase in recycling rate of juvenile crust into the mantle; possibly in response to partial fragmentation of Nuna.
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- Collsional orogens
- Juvenile crust