Oxygen isotopic and chemical compositions of rocks of the Sudbury Basin, Ontario
The whole-rock oxygen isotopic composition of the main units of the Sudbury Irruptive and surrounding rocks has been studied, using samples from two traverses of the North Range and one of the South Range. Norite has an average δ18O of 6.7‰, about 1‰ greater than that of fresh oceanic basalts, and similar to that of some continental basalts. Granophyre is slightly richer in 18O (δ18O = 7.3‰). In neither unit is there significant correlation between δ18O and SiO2 content or degree of alteration as estimated by water content or microscopic appearance. The pervasive hydrous alteration of norite and granophyre apparently occurred in the presence of a small volume of water whose isotopic composition was buffered by the igneous rocks. Inclusion-free devitrified glass ("melt rock") and matrix from the Onaping Formation have δ18O values in the range 6.2 – 12.1‰. Its average δ18O is 8.2‰, comparable to that of Archean gneiss , as required by the model for the origin of the formation as a fallback breccia from a me...