Archean graywackes of the Vermilion volcanic-sedimentary belt were derived in large part from felsic-intermediate volcanic accumulations (mostly dacitic) within the depositional basin. The graywackes are deficient in quartz and potash-feldspar, and are largely made up of volcanic rock fragments and plagioclase. Minor granitic detritus in sedimentary rocks at the eastern end of the belt can be traced to the Saganaga Granite which appears to have intruded the sequence during volcanism and sedimentation. Only fragmentary evidence for other granitic sources has been found.

Grading is common in the graywackes, and other sedimentary structures typical of turbidite sequences are also visible locally despite metamorphism and deformation. Apparently turbidity currents moved volcanic detritus down the slopes of the felsic-intermediate volcanic piles into adjacent parts of the basin.

First Page Preview

First page PDF preview
You do not currently have access to this article.