New Cryogenian, Neoproterozoic, and middle Paleozoic U–Pb zircon ages from the Caledonia terrane, southern New Brunswick, Canada: better constrained but more complex volcanic stratigraphy

Authors

  • Sandra M. Barr Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada
  • Susan C. Johnson New Brunswick Department of Energy and Resource Development, Geological Surveys Branch, Sussex, New Brunswick E4E 5L2, Canada
  • Greg R. Dunning Department of Earth Sciences, Memorial University, St. John’s, Newfoundland and Labrador A1B 3X5, Canada
  • Chris E. White Nova Scotia Department of Energy and Mines, Geological Survey Division, Halifax, Nova Scotia B3J 2T9, Canada
  • Adrian F. Park New Brunswick Department of Energy and Resource Development, Geological Surveys Branch, Fredericton, New Brunswick E3B 5H1, Canada
  • Markus Wälle Department of Earth Sciences, Memorial University, St. John’s, Newfoundland and Labrador A1B 3X5, Canada
  • Amanda Langille Department of Earth Sciences, Memorial University, St. John’s, Newfoundland and Labrador A1B 3X5, Canada

DOI:

https://doi.org/10.4138/atlgeol.2020.007

Abstract

New U–Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 ± 5 Ma and 622 ± 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from crosscutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartzfeldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 ± 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U–Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560–550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a “supereruption/supervolcano” environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560–550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 ± 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 ± 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane.

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Published

2020-07-09

How to Cite

Barr, S. M., Johnson, S. C., Dunning, G. R., White, C. E., Park, A. F., Wälle, M., & Langille, A. (2020). New Cryogenian, Neoproterozoic, and middle Paleozoic U–Pb zircon ages from the Caledonia terrane, southern New Brunswick, Canada: better constrained but more complex volcanic stratigraphy. Atlantic Geoscience, 56, 163–187. https://doi.org/10.4138/atlgeol.2020.007

Issue

Vol. 56 (2020)

Section

Articles

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