Abstract
Abstract—The primary premetamorphic mineral composition of the 4.28 Ga old cummingtonite amphibolites of basalt–andesite composition found in the Nuvvuagittuq foldbelt (Quebec, Canada) is calculated in the MINLITH program. Their mafic and intermediate protoliths were composed of more than one-third quartz clasts and more than 50% Mg–Fe-alumosilicates and silicates (including 30% probably clastic serpentine and chlorite in mafic and intermediate rocks, respectively). The amount of feldspars is insignificant: 5 and 9% in mafic and intermediate rocks, respectively. Such a contrasting composition of clastic material indicates its contribution from various sources. Sediments of such a composition could have been formed under aggressive conditions in the course of weathering of the primary ultramafic crust, Na from which was removed to seawater and K from which accumulated in sedimentary basins, which is evident from the high K2O/Na2O ratio of ≥20. This phenomenon has never happened in the subsequent evolution of the Earth.
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