The Meguma Zone of southern Nova Scotia docked with North America in the mid-Late Devonian. Associated magmatic activity involved small calc-alkaline lamprophyric mafic bodies and large peraluminous granitoid plutons.The mafic bodies include ten dikes and one sheet cutting the Meguma Group metasedimentary rocks, two plugs in the Liscomb Complex, and four synplutonic bodies in some of the smaller granitoid plutons. They are generally coarse-grained hornblende-biotite gabbronorites, diorites, and spessartites, and all have highly fractionated rare earth element patterns and negligible Eu/Eu* anomalies.The granitoid plutons fall into two spatial-chemical-genetic types: 1. The central plutons, including the South Mountain Batholith, are ca. 372 Ma, late-tectonic to posttectonic, predominantly unfoliated, emplaced into low-grade metamorphic host rocks, generally not spatially associated with mafic intrusions, and exclusively peraluminous with Sn-W-Mo-U greisen-and vein-dominated mineral deposits; 2. The peripheral plutons, at the northeastern and southwestern extremities of the Meguma Zone, may be slightly older (376 Ma); they are late-tectonic, moderately foliated, emplaced into higher grade metamorphic host rocks, invariably spatially associated with Late Devonian mafic intrusions, and mostly peraluminous with only limited Be-pegmatite mineralization. The central plutons are apparently entirely crustally derived (sub-Meguma Group source rocks and Meguma Group contamination), and probably owe their origin to crustal thickening associated with the collision of the Meguma terrane against the Avalon terrane. The peripheral plutons are of mixed derivation (sub-Meguma Group source rocks and mantle-derived mafic magmas), and probably owe their origin to the lower to mid-crustal intrusion of subduction-related mafic magmas prior to the final emplacement of the Meguma terrane.
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