Abstract

Twenty-six detrital zircon grains from the late Archaean Pontiac sediments of the Abitibi greenstone belt were dated individually by the U–Pb method in order to identify possible elements of an ancient (pre-2.7 Ga) shield. The results show that at least two components were present at the source areas of these sediments: (1) materials of about 2700–2725 Ma, which were most likely derived from contemporaneous acid igneous rocks; and (2) significantly older materials, parts of which are at least 2940 Ma old, which were either part of an uplifted sedimentary basin or a sialic basement complex. These results can be used to suggest a close link between igneous activity and basin subsidence and that the development of the Abitibi volcanic belt was closely associated with the presence of some older sialic blocks.

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