Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. II. Textures and mineral paragenesis

Abstract

The nepheline-bearing gneisses of the Wolfe Belt in Lyndoch Township, Ontario, have been subjected to textural, fabric, and paragenetic analysis on the basis that they are metamorphic tectonites. In addition, information has been drawn together from various sources bearing upon the relative chronology of Plutonic events, principally metamorphic, diastrophic, and intrusive, of the Grenville orogeny.The alkaline character of the nepheline gneisses has been confirmed as syn-orogenic in origin, apparently forming under upper amphibolite-facies metamorphic conditions during a static interval prior to the second of three recognizable periods of folding. The original 'replacement' textures were largely erased by a penetrative recrystallization during the second period of folding. The Wolfe gneisses principally reflect in their parageneses and textures this metamorphic event. Some textural criteria previously considered to have genetic significance in the origin of the alkaline rocks date from this recrystallization or even later crystalloblastic events. The problem of regional scapolitization is briefly considered. Petrofabric and geological evidence suggest the scapolite developed prior to or early in the third phase of folding.A synthesis of events in the Grenville orogeny as indicated by these rocks is attempted.