THE POSSIBLE GRANITIZATION OF ACIDIC LOWER 

 HURONIAN SCHISTS ON THE NORTH SHORE OF 

 LAKE SUPERIOR 



J. M. BELL 

 Director Geological Survey, Wellington, N. Z. 



The Michipicoten and Pucaswa areas on the north shore of Lake 

 Superior present the apparently extraordinary anomaly of contain- 

 ing a conglomerate well supplied with characteristic granitic pebbles, 

 and of exhibiting no older granitic rock of similar structure from 

 which these pebbles could have been drawn. There are, however, 

 of earlier age, acid schists and gneisses of probable igneous origin, and 

 apparently of like chemical composition, though of different structure 

 from these granitic rocks. I would suggest the possibihty of the 

 derivation of the granitic pebbles in the conglomerate from a pre- 

 existing rock of like characteristics, of which the granite which cuts 

 the conglomerate is the regranitized equivalent. By a regranitized 

 rock I mean one which, originally a granite, quartz-porphyry, or 

 other rock of similar chemical composition and origin, has by meta- 

 morphism been altered into an acid gneiss or schist, and subsequent 

 to the metamorphism — or perhaps in part during the metamorphism — 

 recrystallized back -into a granite. From our present knowledge of 

 the origin of granite, this recrystallization cannot definitely be said 

 to be refusion, and regranitization is perhaps a more correct and 

 exact term. The original granite, the source of the granitic pebbles, 

 may have been the plutonic equivalent of the rock from which the 

 acid gneisses and quartz-porphyry or felsite schists were derived. 

 It is possible that the gneisses may represent the metamorphic rem- 

 nant of the original granite. 



The Michipicoten Mining Division, which contains an area of 

 some 5,000 square miles, is part of the District of Algoma, in Ontario, 

 and is situated on the northeastern shore of Lake Superior, between 

 latitudes 47° 30' and 48° 30'. The division was first set apart by 

 the government of the province of Ontario on account of the aurifer- 



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