An overview of recent bedrock mapping and follow-up petrological studies of the South Mountain Batholith, southwestern Nova Scotia, Canada

Authors

  • Michael A. MacDonald Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada
  • Richard J. Home Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada
  • Michael C. Corey Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada
  • Linda J. Ham Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada

DOI:

https://doi.org/10.4138/1848

Abstract

Recent detailed geological mapping has provided insight into the evolution of the South Mountain Batholith of southwestern Nova Scotia. Mapping has resulted in the delineation of 49 map units consisting of: biotitegranodiorite, biotite monzogranite, muscovite-biotitc monzogranite, coarse- and fine-grained leucomonzogranite and leucogranite; 49 map units have been assigned to thirteen plutons which have been grouped into two stages, including early stage 1 (mostly granodiorite and monzogranite) and late stage 2 (mostly monzogranite, leucomonzogranite, leucogranite). Follow-up petrographic and geochemical studies indicate a continuous sequence from least evolved biotite granodiorite to most evolved leucogranite. In spite of a definitive sequence of emplacement for the plutons and their units, an evaluation of published geochronological data indicates that all plutons were intruded and crystallized during a very short time interval (<5 Ma) at ca. 370 Ma. Various structural characteristics, including the shape and distribution of plutons, the coincidence of several stage 2 plutons with major fault zones, and the orientation of primary and secondary structural features (e.g., megacryst alignment, joints, veins), indicate that the batholith was subjected to regional stresses associated with the waning stages of the Acadian Orogeny during intrusion. The various rock types within the plutons have broadly similar compositions; however, detailed petrographic and geochemical studies have revealed unique compositional characteristics. These differences are explained by variations in protolith composition. Similarly, the style of mineralization in the sundry plutons is interpreted as reflecting the protolith composition and the physio-chemical conditions that prevailed during their crystallization. Accordingly, the economic potential of the thirteen plutons must be evaluated individually. RÉSUMÉ Une nouvelle cartographie géologique détaillée a fourni des données sur l’évolution du batholite du mont South du sud-ouest de la Nouvelle-Écosse. La cartographie a permis de suivre 49 unités qui consistent en: granodiorite à biotite, monzogranite à biotite, monzogranite à biotite et muscovite, leucomonzogranite et leucogranite à grain grossier et fin; les 49 unités ont été assignées à treize plutons qui sont regroupés en deux stades: le stade 1, préeoce (principalement granodiorite et monzogranite), et le stade 2, tardif (principalement monzogranite, leucomonzogranite et leucogranite). Les études pétrographiques et géochimiqucs d'appoint indiquent une suité continue allant des granodio rites a biotite, peu évoluées, aux leucogranitcs, les plus évolués. En dépôt d'une séquence d'intrusion bien définie pour les plutons et leurs unités, une évaluation des données géochronologiques pubiées indique que tous les plutons se sont mis en place et ont cristallisé pendant un interval le très court (<5 Ma), il y a environ 370 Ma. Diverses caractéristiques structurales, dont la forme et la distribution des plutons, la coincidence de plusieurs plutons de stade 2 avec des zones de failles majeures et 1 'orientation des structures primaires et secondares (e.g., alignement des mégacristaux, joints, veines) indiquent que le batholite était soumis, lors de sa mise en place, aux contraintes régionales associées aux stades finaux de l'orogénèse acadienne. Les diverses lithologies à l'intérieur des plutons ont des compositions proches. Cependant, des études pétrogra-phiques et géochimiques détaillées ont révèles des compositions particulières. Ces différences sont expliquées par des variations dans la composition des protolites. De la même maniere, les patrons de minéralisations associées aux divers plutons sont interpréts comme reflétanl la composition du protolite et les conditions physico-chimiques lors de la cristallisation. En conséquence, le potentiel économique des 13 plutons doit Q;tre évalué individuellement. [Traduit par le journal]

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Published

1992-03-01

How to Cite

MacDonald, M. A., Home, R. J., Corey, M. C., & Ham, L. J. (1992). An overview of recent bedrock mapping and follow-up petrological studies of the South Mountain Batholith, southwestern Nova Scotia, Canada. Atlantic Geoscience, 28(1). https://doi.org/10.4138/1848

Issue

Vol. 28 No. 1 (1992)

Section

Articles

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