Syntectonic generation and segregation of tonalitic melts from amphibolite dikes in the lower crust, Striding-Athabasca mylonite zone, northern Saskatchewan

Abstract

The 3.2 Ga Chipman dikes intrude the mylonitized Chipman tonalite within the Striding-Athabasca mylonite zone of northern Saskatchewan. Older dikes are intensely folded and sheared; younger dikes are undeformed. Major and trace element analyses indicate that the dikes are tholeiitic basalts. The youngest, most pristine dikes contain hornblende and plagioclase with minor clinopyroxene and garnet. Older, migmatitic dikes have tonalitic to trondhjemitic segregations spatially associated with garnet crystals. Where small, the segregations occupy tails or strain shadows on every garnet crystal. Where garnets and segregations are large, leucosomes form an interconnected network that extends into the host tonalite. The Chipman dikes are interpreted to have been emplaced, solidified, and partially melted during ductile shearing in the lowermost crust, perhaps near the base of an Archean island arc. -from Authors