Abstract
The origin of silica-undersaturated rocks in the Precambrian polymetamorphic complexes containing unique assemblages with corundum, gedrite, spinel, and other high-Al phases remains debatable [1‐3]. Fluids often play a significant role in their formation, but scales of fluid transfer, the primary composition of source rocks, the degree of their alteration, and the fluid source were not determined. Alternative explanations of the formation of the corundum-bearing rocks are metasomatic reworking of an initially homogeneous sequence accompanied by Al flux or metamorphism of heterogeneous volcanosedimentary rocks. The latter mechanism suggests that the corundum-bearing rocks were formed after aluminous silica-undersaturated rocks. In this paper, we attempted to decipher the origin of the corundum-bearing rocks based on the oxygen isotope study of one of the occurrences of corundumbearing aluminous rocks in northern Karelia (Lake Verkhnee Pulongskoe). The studied object is situated in the Chupa metamorphic sequence (Fig. 1) on Khitostrov Island (Lake Verkhnee Pulongskoe, northern Karelia [4‐6]) [7]. The protoliths of sedimentary and volcanic rocks of the Chupa sequence were metamorphosed in several stages:
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