The Hanna Farm pluton, Cobequid Highlands: petrology and significance for motion on the Kirkhill fault

Authors

  • Georgia Pe-Piper Department of Geology, St Mary's University, Halifax, Nova Scotia B3H 3C3
  • Denise S. Turner Department of Geology, St Mary's University, Halifax, Nova Scotia B3H 3C3

DOI:

https://doi.org/10.4138/1649

Abstract

The Hanna Farm pluton is a complex granite - gabbro pluton which appears to be truncated by the Kirkhill fault zone, probably by predominantly dip-slip motion. A leucogranite has been intruded into the Kirkhill fault zone at the southern end of the Hanna Farm pluton. The main Hanna Farm pluton contains secondary biotite and odier evidence of hydrothermal alteration, and is petrographically and geochemically similar to a series of Early Carboniferous (ca. 345 Ma) granites in the western Cobequid Highlands. Secondary biotite within country rock has been radiomelrically dated at 303 ±11 Ma. The leucogranite within the Kirkhill fault zone lacks evidence of hydro thermal alteration. It shows local ductile deformation, but is not noticeably offset by the Kirkhill fault zone. The Kirkhill fault zone is one of the major east-west trending fault zones in the western Cobequid Highlands. It cuts and mylonitises late Hadrynian sedimentary and plutonic rocks, and probable Early Carboniferous plutons. The Hanna Farm pluton appears to post-date the last major phase of strike-slip motion on the Kirkhill fault RÉSUMÉ Le Pluton de Hanna Farm est un bati complexe de granite et gabbro que semble recouper la zone de failles de Kirkhill, probablement sous L’effet d'un movement à forte composante selon le rejet-pente. Un leucogranite s'est mis en place au sein de la zone de failles de Kirkhill aux confins méridionaux du Pluton de Hanna Farm. Le pluton principal de Hanna Farm contient une biotite secondaire ainsi que d'autres preuves d'une altération hydrothermale. Il ressemble, par sa pétrographie et son géochimisme, à une série de granites éocarboniicres (environ 345 Ma) de l'ouest des Monts Cobequid. Une datation radiométnque de la biotite secondaire que renferme l’encaissant la situea303 ± 11Ma. On ne rencontre aucune trace d'altération hydrothermale dans le leucogranite sis au sein de la zone de failles de Kirkhill. Celui-ci préente une déformation ductile locale mais n'est pas décalé de façon notable par la zone de failles de Kirkhill. Cette dernière est l’une des principales zones de failles à tendance Est-Ouest dans l’ouest des Monts Cobequid. Elle recoupe et mylonitise des roches plutoniques et sédimentaires tardihadryniennes ainsi que des plutons probablement éocarboniferes. Le Pluton de Hanna Farm semble postdater le dernier épisode majeur de décrochement sur la faille de Kirkhill. [Traduit par le journal]

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Published

1988-08-01

How to Cite

Pe-Piper, G., & Turner, D. S. (1988). The Hanna Farm pluton, Cobequid Highlands: petrology and significance for motion on the Kirkhill fault. Atlantic Geoscience, 24(2). https://doi.org/10.4138/1649

Issue

Vol. 24 No. 2 (1988)

Section

Articles

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