Palaeoproterozoic age of a basement gneiss complex in the Charcot Land tectonic window, East Greenland Caledonides

The Charcot Land tectonic window exposes crystalline basement gneisses, which form part of the foreland of the East Greenland Caledonides. These gneisses were previously believed to be Archaean in age, on the basis of imprecise K-Ar analyses carried out in the early 1980s on hornblende from amphibolitic bands and inconclusive Rb/Sr isotope data. New U-Pb singlezircon ion microprobe analyses on the gneisses of the window yield upper intercept ages of 1916 ± 21 and 1928 ± 11 Ma, and are interpreted to represent the age of crystallisation of the igneous protolith. The foreland gneisses of the Charcot Land window are similar in age to parts of the allochthonous gneiss complexes of structurally overlying thrust sheets, but the two terranes have different lithological and structural characteristics. No Archaean rocks have been identified with certainty in any of the East Greenland Caledonian foreland windows.