Petrology, tectonic setting, and crust-mantle interactions of late Devonian tonalitic plutons in the eastern Meguma terrane, Nova Scotia, Canada

Late Devonian tonalitic plutons are associated with more voluminous, coeval granitic plutons in the eastern Meguma terrane of mainland Nova Scotia. The tonalitic plutons range from undeformed to protomylonitic, contain abundant metasedimentary xenoliths, and display magma mingling textures with their adjacent granitic plutons. Lithogeochemical data show peraluminous to metaluminous calc-alkaline compositions. The more geochemically evolved biotite tonalite is related to amphibole-biotite tonalite by crystal fractionation processes. The εNd(t) isotopic compositions are between -1.9 and -2.7, consistent with derivation from a mantle source and subsequent contamination by aluminium-rich crustal rocks to yield peraluminous compositions. Tonalite in plutons in the eastern Meguma terrane is generally less evolved than tonalite in the Barrington Passage, Port Mouton, and Shelburne plutons in the southwestern Meguma terrane. In both areas, tonalitic magmatism likely developed in a subduction zone that experienced slab-failure followed by asthenospheric ascent that generated melting of the metasomatized lithospheric mantle to produce the mantle-derived tonalitic magmas. Those magmas were subsequently contaminated by an aluminum-rich lower crust and underwent crystal fractionation. Associated granitic plutons likely resulted from lower crustal anatexis caused by the ascent of the hot mantle-derived tonalitic magmas.