LE3 .A278 2018

2018

Barr, Sandra

Acadia University

Master of Science

Masters

Geology

Earth & Environmental Sciences

The Margaree pluton extends for 40 km along the central axis of the Ganderian Aspy terrane of northern Cape Breton Island, Nova Scotia. Previously described as rapakivi-textured megacrystic syenogranite, detailed mapping and U-Pb (zircon) dating showed that the pluton consists of three units of similar age: (1) Second Fork Brook megacrystic syenogranite (363.1 ±1.6 Ma); (2) Northeast Margaree River equigranular syenogranite (364.8 ± 1.6), and (3) North Branch Margaree River porphyry (365.5 ± 3.3 Ma). Although the units display wide textural variation, conserved element analysis and Pearce element ratio analysis indicates that they are comagmatic, and that their chemical variation can be attributed to the fractionation of quartz, K-feldspar, and Na-rich plagioclase. The isotopic signature of the Margaree pluton indicates that it was derived from melting of recycled continental crust, and that its evolved orogenic chemical signature can be attributed to inheritance. The magma that formed the Margaree pluton resulted from the melting of HPE-enriched source area, possibly triggered by the intrusion of mafic magmas in an extensional tectonic environment, following the conclusion of the orogenic activity and during regional uplift and cooling. The resulting magma ascended through the continental crust at the point where the Aspy fault intersected the contact between the Belle Cote Road orthogneiss and the Taylors Barren pluton. The presence of megacrysts and rapakivi texture can be attributed to thermal perturbation in the magma chamber caused by mixing of felsic and mafic magmas. The Margaree pluton is interpreted as a mixed silicic-mafic pluton, emplaced at shallow depth, even though direct evidence of mafic magmatism is lacking at the level of the pluton currently exposed.

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https://scholar.acadiau.ca/islandora/object/theses:2699