Stephanie Woodend (Douma)

The Port Mouton Pluton (PMP) is a complex, peraluminous, post-tectonic body located in southern Nova Scotia, that is distinct from the northern plutons and batholiths of the northeastern Meguma Terrane. The pluton consists of ten mappable units, which collectively range in composition from tonalite, to trondhjemite, granodiorite, monzogranite, leucomonzogranite, aplite, pegmatite and lamprophyre.

The PMP evolved in three mafic-to-felsic cycles defined by the initial mafic end-members for each cycle (Units 1, 4 and 7). These three units are the most volumetrically abundant of the ten units and Unit 1 is the oldest of the ten units. Shoshonitic lamprophyres intruded mid-way through Cycle II and were subsequently intruded by phases in Cycle III.

The PMP is at least 352 million years old (⁴⁰Ar/³⁹Ar) but is demonstrably younger than the regional metamorphic age of 395 million years. The lamprophyre dykes are at least 328 million years old. Two distinct foliations observed within the pluton occur only in Units 1 and 4. The foliation in Unit 1 is perpendicular to the foliation of the country rock and is probably of igneous origin. The local foliation observed in Unit 4 is perpendicular to Unit 1 and parallel to the foliation in the country rock. Its origin is unknown.

Minor migmatization is present along some margins of the PMP but the contacts with the metasediments are predominantly sharp. The pluton was emplaced at a pressure of approximately 3.5 kilobars and temperatures of at least 650^oC.

Both mineral-chemistry and whole-rock chemical analyses suggest that Unit 1 is distinct from Unit 4. Simple, fractional crystallization cannot adequately explain the major and trace element variations observed between Unit 1 and Unit 4 but there is some evidence to support a crystal fractionation model evolving Unit 7 tonalites and granodiorites from Unit 1 tonalites.

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Pages: 345
Supervisors: D. Barrie Clarke