LE3 .A278 2012

2012

Barr, Sandra

Acadia University

Master of Science

Masters

Geology

Earth & Environmental Sciences

The Trafalgar Plutonic Suite, located in the northeastern part of the Meguma terrane in central Nova Scotia, intruded metasedimentary rocks of the Goldenville and Halifax groups at about 374 Ma, based on published U-Pb (zircon) and 40Ar/39Ar mica ages from several plutons in the suite. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular, porphyritic, or megacrystic) and modal mineralogy (quartz diorite, tonalite, granodiorite, monzogranite, or syenogranite). The granodiorite, monzogranite and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the tonalite/quartz diorite plutons show petrographic and chemical variation, both within and between plutons. Based on different chemical characteristics and trends, it is unlikely that the granodiorite, monzogranite and syenogranite magmas were comagmatic with the tonalite/quartz diorite magma(s). The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The tonalite/quartz diorite plutons chemically resemble the minor Devonian mafic intrusions of the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has characteristics of volcanic-arc to syn-collisional granitoid rocks. Underplating by mafic magma, perhaps represented by the tonalite/quartz diorite plutons, may have facilitated melting of the lower crust to generate the granodioritic parent magmas followed by crystal fractionation and subsequent contamination by metasedimentary material, including the Goldenville and Halifax groups.

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https://scholar.acadiau.ca/islandora/object/theses:230