Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data

2002/01/01 by D Fraser Keppie, D. Fraser Keppie, J Duncan Keppie +3 · 15 citations
Computer Science · Earth and Planetary Sciences · #Anticline #Crenulation #Fold (higher-order function) #Geochemistry #Geochemistry and Geologic Mapping #Geological and Geochemical Analysis #Geology #Metamorphic rock #Metamorphism #Seismology #Shear zone #Tectonics #Terrane #earthquake and tectonic studies

paper · doi:10.1139/e01-058

published in Canadian Journal of Earth Sciences 39(1), 53-63 (NRC Research Press)

openalex publication_date 2002/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/25

Abstract

Many auriferous veins dated at ~370 Ma in the Meguma terrane of Nova Scotia are concentrated in tight domes, and conical fold hinges that are transected by 378 Ma low-pressure and high-temperature metamorphic isograds and 380–370 Ma granitoid plutons. Published experiments suggest that such folds are diachronous initiating at inhomogeneities and propagating both in amplitude and along their length. Thus fold terminations are typically conical in geometry and record only the youngest increment of folding. The northeastern termination of the Oldham anticline is characterized by (1) a conical fold, (2) saddle reef auriferous veins, (3) divergent and convergent cleavage fans, (4) a downdip lineation on the slaty cleavage defined by biotitic mineral aggregates inferred to have developed during fold growth. The age of the biotitic mineral aggregates is bracketed between peak metamorphism at > 600°C, defined by a nearly concordant 378 Ma U–Pb monazite age from a xenolith in lamprophyre dyke, and ~366 Ma 40 Ar/ 39 Ar muscovite–biotite ages, recording cooling through ~400–300°C. This suggests that the conical termination of the Oldham anticline grew between 378 and 366 Ma, an observation that reconciles the empirical structural control of the saddle reef auriferous veins with the ~370 Ma age dating of vein minerals. Application of this conclusion to saddle reef auriferous veins in domes suggests that mineralization was related to the youngest increment of fold amplification.

Citations

• Detrital and metamorphic 40Ar/39Ar ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia
• Deep seismic reflection data from the Bay of Fundy and Gulf of Maine: tectonic implications for the northern Appalachians
• 440 Ma igneous activity in the Meguma Terrane, Nova Scotia, Canada; part of the Appalachian overstep sequence?
• Late Paleozoic collision, delamination, short-lived magmatism, and rapid denudation in the Meguma Terrane (Nova Scotia, Canada): constraints from 40Ar/39Ar isotopic data
• Late Devonian lamprophyric dykes in the Meguma Zone of Nova Scotia

Cited by

• A paleogeographical review of the peri-Gondwanan realm of the Appalachian orogen1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

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• New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada
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• The Goldenville–Halifax transition, Mahone Bay, Nova Scotia: relative sea-level rise in the Meguma source terrane
• 440 Ma igneous activity in the Meguma Terrane, Nova Scotia, Canada; part of the Appalachian overstep sequence?