Petrology and tectonic setting of mafic-intermediate plutons and dykes in the eastern Meguma Terrane, Nova Scotia, Canada
LE3 .A278 2022
Master of Science
Earth & Environmental Science
Earth & Environmental Sciences
Small plutons of mafic to intermediate composition are locally associated with the abundant Devonian granitic plutons that intruded the Goldenville and Halifax groups in the eastern Meguma terrane of mainland Nova Scotia. In addition, a swarm of mafic-intermediate dykes, here termed the Eastern Shore dykes, occur in the coastal part of that area. The purpose of this study is to investigate the petrology, petrogenesis, and tectonic implications of these mafic-intermediate plutons and mafic dykes. The Garry Lakes, Cranberry Lake, and the mafic-intermediate plutons (Porcupine Lake, Bog Island Lake, Mink Lake, and Ten Mile Lake plutons) in the Trafalgar plutonic suite make up the tonalite to quartz diorite intrusions. They range from undeformed to protomylonitic, contain abundant metasedimentary xenoliths, and show magma mingling textures with their adjacent granitic plutons. Small quartz diorite to diorite intrusions occur nearby including the younger Melrose Dyke and the Moose Lake diorite. The Eastern Shore dykes have dominant mineralogy and geochemical characteristics of the lamprophyre variety spessartite. These mafic-intermediate intrusions are dominantly calc-alkaline and peraluminous to metaluminous. Chemical comparison to the associated granitic plutons suggest the granitic intrusions could be a result of anatexis caused by the ascent of the hot, mantle-derived magmas. Similar chemical affinities are identified between the eastern mafic-intermediate intrusion with the mafic-intermediate intrusions in southwestern Meguma terrane. Geochemical data support that mafic-intermediate intrusions in the eastern Meguma terrane were derived from a mantle source. The mafic-intermediate magmatism in the eastern Meguma terrane may have been generated in a subduction zone that experienced slab-breakoff that caused the asthenosphere to rise and melt the metasomatized lithospheric mantle to produce the mantle-derived magmas and lamprophyres.
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