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Geological Survey of Canada, 3303-33rd Street N. W., Calgary, Alberta T2L 2A7, Canada
The Kisseynew sedimentary gneiss belt forms part of an early Proterozoic accretionary margin preserved between two Archaean cratons in the south-west Canadian Shield. The sediments are volcanogenic turbidites deposited from flanking volcanic belts at 1910–1875 Ma. Two compressional tectonic events preceded 1815 Ma metamorphism, which reached conditions of 750°C at about 5.5 kbar. Subsequent uplift took the rocks through to 280°C at about 1705 Ma. Thermal modelling suggests that, over this time interval, the average uplift rate was 0.06 km Ma–1. The K, U and Th analyses of the metasediments, combined with the estimated burial depth, show that in situ radiogenic heat production was insufficient to cause the high-temperature, moderate-pressure metamorphism. A modern analogy in southern Alaska suggests that elevated thermal flux due to magmatic intrusion may be a common phenomenon during the late stages of evolution of accretionary environments.
