Petrology, mineralization potential, and tectonic setting of late Devonian plutons in the central Cape Breton Highlands, Nova Scotia, Canada.

The West Branch North River (WBNR), Bothan Brook (BB), Centre Road (CR), and Peter Brook (PB) plutons are in the Aspy terrane of central Cape Breton Island, part of Ganderia in the northern Appalachian orogen. The plutons are elongate parallel to regional trends but are undeformed and appear to have been emplaced after Acadian deformation in the area. U-Pb zircon dating has confirmed previously assumed late Devonian ages of ca. 370-360 Ma. No petrological studies have been done on these plutons since the 1980s, and their mineralization potential and tectonic setting have not been investigated. Preliminary petrographic examination of cut slabs and thin sections from about 40 samples collected as part of regional mapping projects that included these plutons show a wide range in rock types from monzodiorite to syenogranite. Samples from WBNR, BB, and PB plutons consist mostly of medium-to coarse-grained equigranular biotite monzogranite, whereas the CR pluton includes both hornblende-biotite monzodiorite and quartz monzonite. Chemical analyses of 33 samples range in SiO2 content from about 53% to 77%, with lowest contents in samples from the CR pluton and the highest in the BB pluton. Most samples have high K2O contents suggesting that they are of shoshonitic affinity. Trace element compositions indicate that they formed in a subduction-related environment, perhaps from magmas generated in a post-collisional slab-failure tectonic setting. Although no mineralization has been observed, the highly evolved compositions in the BB pluton suggest some potential for Li or other critical elements. [ABSTRACT FROM AUTHOR]