Geology and U-Pb geochronology of the Annidale Group, southern New Brunswick: Lower Ordovician volcanic and sedimentary rocks formed near the southeastern margin of lapetus Ocean

Auteurs-es

  • M. J. McLeod Department of Natural Resources and Energy, Geological Surveys Branch, P.O. Box 1519, (Picadilly Road), Sussex, New Brunswick EOE IPO, Canada
  • A. A. Ruitenberg Department of Natural Resources and Energy, Geological Surveys Branch, P.O. Box 1519, (Picadilly Road), Sussex, New Brunswick EOE IPO, Canada
  • T. E. Krogh Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada

DOI :

https://doi.org/10.4138/1860

Résumé

Geological mapping and U-Pb (zircon) dating have led to the discovery of distinctive Lower Ordovician volcano-sedimentary rocks in the Annidale area of southern New Brunswick. These rocks are included in a newly defined group, herein termed the Annidale Group, which is divided into three fault bounded(?) units of partially overlapping age. These units are named the East Scotch Settlement Formation, the Lawson Brook Formation and the Canaan Forks sequence, from south to north. The East Scotch Settlement Formation contains a steeply dipping succession of mixed mafic and felsic volcanic rocks and a variety of clastic and volcanogenic sedimentary rocks. The Lawson Brook Formation constitutes a shallowly to moderately north-dipping succession dominated by felsic volcanic rocks. The Canaan Forks sequence, most of which constitutes a shallowly to moderately north-dipping succession, is dominated by clastic sedimentary rocks. Structurally, much of the Annidale Group is characterized by intense shearing produced by numerous vertical northeast- and northwest-trending faults and by southward- and northward-directed thrust faults. In the vicinity of these structural features, the East Scotch Settlement Formation is further characterized by pervasive carbonatization that is commonly accompanied by base-metal- and gold-bearing silicification and high chromium-mica alteration zones. Zircons from a felsic dome in the East Scotch Settlement Formation and from felsic schists in the Lawson Brook Formation yield U-Pb dates of 493 ± 2 Ma and 497 ±10 Ma, respectively. Based on these dates and constituent lithologies, the Annidale Group is tentatively correlated with parts of the Cookson Group to the southwest. RÉSUMÉ La cartographie géologique et les datations U-Pb sur les zircons ont mené à la découverte de roches volcaniques et sédimentaires distinctives, de l’Ordovicien intérieur, dans la région d 'Annidale du sud du Nouveau-Brunswick. Ces roches sont comprises dans un Groupe nouvellement défini, nommé ici le Group d'Annidale, qui est divisé en trois unités possiblement bordées par des failles et dont les âges se recouvrent partiellement. Ces unités sont nommées, du nord au sud: la Formation de East Scotch Settlement, la Formation du Ruisseau Lawson et la séquence de Can nan Forks. La Formation de East Scotch Settlement contient une succession à pendage abrupt de volcanites mafiques et felsiques et un assemblage varié de roches sédimentaires clastiques et volcanogènes. La Formation du Ruisseau Lawson consiste en une succession à pendage faible ou modéré vers le nord dominée par les volcanites felsiques. La séquence de Cannan Forks, dont la majeure partie est une succession à pendage faible ou modéré vers le nord, est dominée par les roches sédimentaires clastiques. Structuralement, une bonne partie du Groupe d'Annidale est caractérisée par un cisaillcment intense produit par de nombreuses failles verticales nord et nord-est et par des failles de chevauchement vers le sud et le nord. A proximité de ces failles, la Formation de East Scotch Settlement est caractérisée par une carbonatation intense qui est commundment accompagnée par une silicification porteuse de métaux de base et d'or et de zones d'altération à mica chromifere. Les zircons d'un dome felsique dans la Formation de East Scotch Settlement et de schistes felsiques dans la Formation du Ruisseau Lawson ont donné des âges U-Pb de 493 ± 2 Ma et 497 ± 10 Ma, respectivement. Sur la base de ces datations et de similarity lithologiques, le Groupe d'Annidale est tentativement corré1é avec des parties du Groupes de Cookson, situé au sud-ouest. [Traduit par le journal]

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Publié-e

1992-07-01

Comment citer

McLeod, M. J., Ruitenberg, A. A., & Krogh, T. E. (1992). Geology and U-Pb geochronology of the Annidale Group, southern New Brunswick: Lower Ordovician volcanic and sedimentary rocks formed near the southeastern margin of lapetus Ocean. Atlantic Geoscience, 28(2). https://doi.org/10.4138/1860

Numéro

Vol. 28 No. 2 (1992)

Rubrique

Articles

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