Field relationships, mineralogy and structural features of the Port Mouton pluton, southwestern Nova Scotia
DOI:
https://doi.org/10.4138/1852Abstract
The Port Mouton pluton (PMP) of southern Nova Scotia is a complex, per aluminous, post-tectonic granitoid body that is distinct from other plutons and batholiths of the Meguma Terrane. The pluton consists of ten 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. Shoshonitic lamprophyres intruded mid-way through cycle II and were subsequently intruded by units in cycle III. The PMP is at least 352 Ma (40Ar/39Ar) and is demonstrably younger than the regional metamorphism of 395 Ma. Two distinct foliations observed within the pluton occur only in units 1 and 4. The foliation in unit 1 is perpendicular to the regional foliation of the country rocks and is probably of igneous origin. The local foliation in unit 4, the origin of which remains unknown, is perpendicular to that in unit 1 and parallel to the regional foliation in the country rocks. Contacts of the PMP with the host metasedimentary rocks are predominantly sharp, although minor migmatization is present locally. RÉSUMÉ Le pluton de Port Mouton (PMP) du sud de la Nouvelle-Écosse est une masse granitique complexe, pcralumineuse et post-tectonique, qui se distingue des autres plutons et batholites du terrain de Meguma. Le pluton consiste en dix unités, allant des tonalites aux trondhjemites, granodiorites, monzogranites, leucomonzogranites, aplites, pegmatites et lamprophyres. L'évolution du PMP se divise en trois cycles mafiques à felsiques deTmis par les termes mafiques de chaque cycle (unités 1, 4 et 7). Ces trois unités sont les plus abondantes et l'unité 1 est la plus ancienne. Des lamprophyres shoshonitiques se sont mis en place vers le milieu du cycle II et ont été subséquemment recoupés par les unités du cycle III. Le PMP a un âge minimum de 352 Ma (40Ar/39Ar) mais prédate le métamorphisme régional daté à 395 Ma. Les deux foliations distinctes observéers dans le pluton ne se retxouvent que dans les unités 1 et 4. La foliation dans l’unité 1 est perpendiculaire à la foliation régionale des roches encaissantes et est probablement d’origine ignée. La foliation locale dans l’unité 4, dont l'origine reste obscure, est perpendiculaire à celle de l’unité 1 et est parallèle à la foliation régionale des roches encaissantes. Les contacts du PMP avec les roches métasédimentaires éncaissantes sont principalement nets, bien qu'il y ait de la migmatisation locale. [Traduit par le journal]Downloads
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