Granite and associated mafic phases, North River pluton, Cobequid Highlands, Nova Scotia

Abstract

The North River pluton is one of a series of upper Devonian - lower Carboniferous granite and gabbro/diorite plutons in the Cobequid Highlands. It lies within a regional zone of east-west strike-slip faulting associated with the Cobequid Fault. The pluton consists of a single main granite unit that intruded small marginal bodies of gabbro. A relative sequence of intrusion can be determined from cross-cutting relationships. Hybrid rocks demonstrate that some of the mafic magma was intruded synchronously with granitic magma. The granite is a subalkalic A-type granite. The mafic rocks show "within-plate' characteristics. Enrichment in Rb and K in the northeastern part of the pluton reflects a late metasomatic event. The Devono-Carboniferous plutons of the Cobequid Highlands differ from other published examples of shear zone plutonism in that magma generation appears to have been related to either local or more probably regional extension rather than the shear zone having tapped a magma that originally resulted from either subduction or continental collision. -from Author