Résumés
Abstract
The ca. 370 Ma Eastern Shore dykes include six single or multiple (two or three) parallel spessartite dykes that trend NNW in the Sheet Harbour area of eastern mainland Nova Scotia. Spessartite is a variety of calc-alkaline lamprophyre that characteristically occurs in dykes associated with granitoid rocks and gold mineralization in orogenic belts. Spessartite dykes typically contain crustal xenoliths and xenocrysts, a feature shown by three of the Eastern Shore dykes (Popes Harbour, Tuff Island, and Borgles Island). The Eastern Shore dykes are mineralogically and chemically typical of spessartite but show wide chemical variation and higher MgO, lower TiO2 and P2O5, and flatter chondrite-normalized rare-earth-element patterns than are typical of spessartite. The pair of dykes at Sober Island show internal variations that are evidence of magma evolution resulting from plagioclase and amphibole fractionation; the East Jeddore and Little Harbour Road and Coast dykes are similar to the least evolved Sober Island spessartite. The three xenolith/xenocryst-bearing dykes show anomalous chemical features such as more enrichment in light rare-earth elements (REE), higher Sr, Y, Zr, and Hf, and more varied compositions compared to the other dykes. The Popes Harbour dyke is characterized by low Ni. Despite these differences, mainly parallel chondrite-normalized REE patterns suggest that the Eastern Shore dykes are related and derived from hydrous large-ion-lithophile- and high-field strength-element-enriched garnet-bearing mantle-derived magma that experienced variable crustal contamination.
Keywords:
- Meguma terrane spessartite,
- calc-alkalic lamprophyre,
- whole-rock geochemical data,
- subcontinental li
Résumé
Les dykes de la côte est, qui remontent à environ 370 Ma, comprennent six dykes parallèles de spessartite, simples ou multiples (deux ou trois), orientés vers le nord-nord-ouest dans le secteur de Sheet Harbour, dans l'est de la partie continentale de la Nouvelle-Écosse. La spessartite est une variété de lamprophyre calcoalcalin habituellement présent dans des dykes associés à des roches granitoïdes et à une minéralisation aurifère dans les ceintures orogéniques. Les dykes de spessartite renferment généralement des xénolites et des xénocristaux crustaux, une caractéristique relevée dans trois des dykes de la côte est (Popes Harbour, île Tuff et île Borgles). Les dykes de la côte est sont similaires à la spessartite sur les plans minéralogique et chimique, mais ils présentent une diversité marquée des compositions chimiques, des teneurs supérieures en MgO, des teneurs inférieures en TiO2 et P2O5, et des spectres des terres rares normalisés aux valeurs chondritiques plus plats que ceux habituellement observés dans la spessartite. La paire de dykes de l’île Sober affiche une diversité interne qui témoigne d’une évolution du magma résultant du fractionnement du plagioclase et de l'amphibole; les dykes d’East Jeddore et de la côte et du chemin Little Harbour sont analogues à la spessartite de l’île Sober la moins évoluée. Les trois dykes abritant des xénolites/xénocristaux présentent des caractéristiques chimiques anomales telles qu'un enrichissement plus important en éléments des terres rares légers (ÉTR), des concentrations plus élevées en Sr, Y, Zr et Hf, ainsi que des compositions plus variées que les autres dykes. Le dyke de Popes Harbour se distingue par une faible teneur en Ni. Malgré ces différences, les spectres principalement parallèles des terres rares normalisés aux valeurs chondritques laissent supposer que les dykes de la côte est sont apparentés et dérivés d'un magma mantellique grenatifère hydraté, enrichi en éléments lithophiles à grand rayon ionique et à haute intensité, ayant subi une contamination crustale variable.
Parties annexes
Bibliography
- Archibald, D.B., Murphy, J.B., Reddy, S.M., Jourdan, F., Gillespie, J., and Glorie, S. 2018. Post-accretionary exhumation of the Meguma terrane relative to the Avalon terrane in the Canadian Appalachians. Tectonophysics, 747, pp. 343–356. https://doi.org/10.1016/j.tecto.2018.10.016
- Archibald, D.B., Barr, S.M., White, C.E., Nickerson, S.J., Stern, R.A., Luo, Y., and Pearson, G.D. 2025. Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U–Pb, Lu–Hf and O isotopic compositions, age, and petrogenetic implications. Canadian Journal of Earth Sciences, 62, pp. 381–400 https://doi.org/10.1139/cjes-2024-0023
- Barr, S.M., White, C.E., and Pin, C. 2022. Revised stratigraphy in the eastern Meguma terrane, Nova Scotia, Canada, and variations in whole-rock chemical and Sm–Nd isotopic compositions of the Goldenville and Halifax groups. Atlantic Geoscience, 58, pp. 193–213. https://doi.org/10.4138/atlgeo.2022.008
- Bickerton, L., Kontak, D.J., Murphy, J.B., Kellett, D.A., Samson, I.M., Marsh, J.H., Dunning, G., and Stern, R. 2022. The age and origin of the South Mountain Batholith (Nova Scotia, Canada) as constrained by zircon U–Pb geochronology, geochemistry, and O–Hf isotopes. Canadian Journal of Earth Sciences, 59, pp. 418–454. https://doi.org/10.1139/cjes-2021-0097
- Choi, E., Fiorentini, M.L., Hughes, H.S.R., and Giuliani, A. 2020. Platinum-group element and Au geochemistry of Late Archean to Proterozoic calc-alkaline and alkaline magmas in the Yilgarn Craton, Western Australia. Lithos, pp. 374–375, https://doi .org /10 .1016 /j .lithos .2020 .105716
- Clarke, D.B., MacDonald, M.A., and Tate, M.C. 1997. Late Devonian mafic-felsic magmatism in the Meguma Zone, Nova Scotia. In The Nature of Magmatism in the Appalachian Orogen. Edited by A.K. Sinha, J.F. Whalen, and J.P. Hogan. Geological Society of America Memoir, 191, pp. 107–127. https://doi.org/10.1130/0-8137-1191-6.107
- Collins, W.J. and Murphy, J.B. 2025. Conjugate shear model for emplacement of mid-crustal plutons during dextral transpression, southern Nova Scotia, Canada: tectonic and petrological consequences. Canadian Journal of Earth Sciences, 62, pp. 152–170. https://doi.org/10.1139/cjes-2024-0044
- Culshaw, N. and Lee, S.K. 2006. The Acadian fold belt in the Meguma Terrane, Nova Scotia: Cross sections, fold mechanisms, and tectonic implications. Tectonics, 25, Article no. TC3007, 16 pp. https://doi.org/10.1029/2004TC001752
- Culshaw, N. and Reynolds, P. 1997. 40Ar/39Ar age of shear zones in the southwest Meguma Zone between Yarmouth and Meteghan, Nova Scotia. Canadian Journal of Earth Sciences, 34, pp. 848–853. https://doi.org/10.1139/e17-069
- Eberz, G.W., Clarke, D.B., Chatterjee, A.K., and Giles, P.S. 1991. Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone, Nova Scotia: evidence from granulite facies xenoliths. Contributions to Mineralogy and Petrology, 109, pp. 69–88. https://doi.org/10.1007/BF00687201
- Gan, Y. 2023. Composition and origin of xenocrysts in the Eastern Shore spessartite dykes, Nova Scotia. Unpublished BSc honours thesis, Acadia University, Wolfville, Nova Scotia, 98 p.
- Giles, P.S. and Chatterjee., K. 1987. Lower crustal xenocrysts and xenoliths in the Tangier dyke, eastern Meguma Zone, Nova Scotia. In Mines and Minerals Branch, Report of Activities 1987, part A. Edited by J. L. Bates and D. R. MacDonald. Nova Scotia Department of Mines and Energy, Report 87-5, pp. 85–88.
- Greenough, J.D., Ruffman, A., and Owen, J.V. 1988. Magma injection directions inferred from a fabric study of the Popes Harbour dike, eastern shore, Nova Scotia, Canada. Geology, 16, pp. 547–550. https://doi.org/10.1130/0091-7613(1988)016<0547:MIDIFA>2.3.CO;2
- Greenough, J.D., Owen, J.V., and Ruffman, A. 1993. Noble metal concentrations in shoshonitic lamprophyres: analysis of the Weekend dykes, Eastern Shore, Nova Scotia, Canada. Journal of Petrology, 34, pp. 1247–1269. https://doi.org/10.1093/petrology/34.6.1247
- Greenough, J.D., Krogh, T.E., Kamo, S.L., Owen, J.V., and Ruffman, A. 1999. Precise U–Pb dating of Meguma basement xenoliths: new evidence for Avalonian underthrusting. Canadian Journal of Earth Sciences, 36, pp. 15–22. https://doi.org/10.1139/e98-079
- Hanson, G.N. 1980. Rare earth elements in petrogenetic studies of igneous systems. Annual Review of Earth and Planetary Sciences, 8, pp. 371–406. https://doi.org/10.1146/annurev.ea.08.050180.002103
- Hawthorne, F.C., Oberti, R., Harlow, G.E., Maresch, W.V., Martin, R.F., Schumacher, J.C., and Welch, M.D. 2012. Nomenclature of the amphibole supergroup. American Mineralogist, 97, pp. 2031–2048. https://doi.org/10.2138/am.2012.4276
- Hibbard, J.P., van Staal, C.R., Rankin, D.W., and Williams, H. 2006. Lithotectonic map of the Appalachian Orogen, Canada–United States of America. Geological Survey of Canada, Map 2096A, scale 1:1 500 000. https://doi.org/10.4095/221912
- Hicks, R.J., Jamieson, R.A., and Reynolds, P.H. 1999. Detrital and metamorphic 40Ar/39Ar ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia. Canadian Journal of Earth Sciences, 36, pp. 23–32. https://doi.org/10.1139/e98-081
- Hutchinson, C.S. 1974. Laboratory handbook of petrographic techniques. Wiley Interscience, New York, 527 p.
- Irvine, T.N. and Baragar, W.R.A. 1971. A guide to the chemical classification of the common volcanic rocks. Canadian Journal of Earth Science, 8, pp. 523–548. https://doi.org/10.1139/e71-055
- Jackson, H.R., Chian, D., Funck, T., Barr, S.M., Shimeld, J., White, C.E., Salisbury, M. 2024. Geological interpretation of wide-angle seismic reflection/refraction profiles along the Scotian margin and across Nova Scotia, Canada. Tectonophysics, 879, Article no. 230315, 19 pp. https://doi.org/10.1016/j.tecto.2024.230315
- Kempster, R. 1988. A comparative petrological study of three Nova Scotian intrusions: the Jeddore dyke, the Sober Island dyke, and the Marshdale intrusive. Unpublished BSc thesis, Dalhousie University, Halifax, Nova Scotia, 94 p.
- Kempster, R., Clarke, D., Reynolds, P., and Chatterjee, A. 1989. Late Devonian lamprophyric dykes in the Meguma zone of Nova Scotia. Canadian Journal of Earth Sciences, 26, pp. 611–613. https://doi.org/10.1139/e89-052
- Keppie, J.D. and Dallmeyer, R.D. 1995. Late Paleozoic collision, delamination, short-lived magmatism, and rapid denudation in the Meguma Terrane (Nova Scotia, Canada): constraints from 40Ar/39Ar isotopic data. Canadian Journal of Earth Sciences, 32, pp. 644–659. https://doi.org/10.1139/e95-054
- Kontak, D.J., Smith, P.K., and Reynolds, P.H. 1993. Geology and 40Ar/39Ar geochronology of the Beaver Dam gold deposit, Meguma Terrane, Nova Scotia, Canada: evidence for a 370 Ma age of mineralization. Economic Geology, 88, pp. 139–170. https://doi.org/10.2113/gsecongeo.88.1.139
- Kontak, D.J., Horne, R.J., Sandeman, H., Archibald, D., and Lee, J.K.W. 1998. 40Ar/39Ar dating of ribbon-textured veins and wall-rock material from Meguma lode gold deposits, Nova Scotia: implications for timing and duration of vein formation in slate-belt hosted vein gold deposits. Canadian Journal of Earth Sciences, 35, pp. 746–761. https://doi.org/10.1139/e98-028
- Kontak, D.J., Ham, L.J., and Dunning, G.R. 2004. U–Pb dating of the Musquodoboit Batholith, southern Nova Scotia: evidence for a protracted magmatic-hydrothermal event in a Devonian intrusion. Atlantic Geology 40, 207–216. https://doi.org/10.4138/1040
- Krmíček, L. and Rao, N.V. 2021. Lamprophyres, lamproites and related rocks as tracers to supercontinent cycles and metallogenesis. In Lamprophyres, lamproites and related rocks: tracers to supercontinent cycles and metallogenesis: Introdution. Edited by L Krmíček and N.V. Rao. Geological Society, London, Special Publications, 513, pp. 1–16. https://doi.org/10.1144/SP513-2021-159
- Krmíček L., Cempírek J., Havlín A., Přichystal A., Houzar S., Krmíčková M., and Gadas P. 2011. Mineralogy and petrogenesis of a Ba–Ti–Zr-rich peralkaline dyke from Šebkovice (Czech Republic): recognition of the most lamproitic Variscan intrusion. Lithos, 121, 74–86. https://doi.org/10.1016/j.lithos.2010.10.005
- Locock, A. J. 2014. An Excel spreadsheet to classify chemical analyses of amphiboles following the IMA 2012 recommendations. Computers and Geosciences, 62, pp. 1–11. https://doi.org/10.1016/j.cageo.2013.09.011
- MacDonald, M.A. and Clarke, D.B. 2017. Occurrence, origin, and significance of melagranites in the South Mountain Batholith, Nova Scotia. Canadian Journal of Earth Sciences, 54, pp. 1–21. https://doi.org/10.1139/cjes-2016-0106
- Mahoney, K.L. 1996. The contact metamorphic aureole of the South Mountain Batholith, Nova Scotia. Unpublished MSc thesis. Wolfville, Nova Scotia, 153 p.
- Müller, D. and Groves, D.I. 2016. Indirect associations between lamprophyres and gold-copper deposits. In Potassic igneous rocks and associated gold-copper mineralization. Edited by D. Müller, and D.I. Groves. Springer International, pp. 203–226. https://doi.org/10.1007/978-3-319-23051-1_8
- Nickerson, S.J. 2022. Petrology and tectonic setting of mafic-intermediate plutons and dykes in the eastern Meguma terrane, Nova Scotia, Canada. Unpublished MSc Thesis. Acadia University, Wolfville, Nova Scotia, 221 p.
- Owen, J.V. and Greenough, J.D. 1991. An empirical sapphirine–spinel Fe–Mg exchange thermometer and its application to high-grade xenoliths in the Popes Harbour dyke, Nova Scotia. Lithos, 26, pp. 317–332. https://doi.org/10.1016/0024-4937(91)90036-K
- Owen, J.V., Greenough, J.D., Hy, C., and Ruffman, A. 1988. Xenoliths in a mafic dyke at Popes Harbour, Nova Scotia: implications for the basement to the Meguma Group. Canadian Journal of Earth Sciences, 25, pp. 1464–1471. https://doi.org/10.1139/e88-139
- Pearce, J.A. 1983. Role of the sub-continental lithosphere in magma genesis at active continental margins. In Continental basalts and mantle xenoliths. Edited by C.J. Hawkesworth and M.J. Norry. Shiva, Orpington. pp. 230–249.
- Peccerillo, A. and Taylor, S.R. 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contributions to Mineralogy and Petrology, 58, pp. 63–81. https://doi.org/10.1007/BF00384745
- Raeside, R.P. and Jamieson, R.A. 1992. Low-pressure metamorphism of the Meguma terrane, Nova Scotia. Field excursion C-5, GAC-MAC field trip guide, 25 p.
- Raeside, R.P., Hill, J.D., and Eddy, B.G. 1988. Metamorphism of Meguma Group metasedimentary rocks, Whitehead Harbour area, Guysborough County, Nova Scotia. Maritime Sediments and Atlantic Geology, 24, pp. 1–9. https://doi.org/10.4138/1635
- Rock, N.M.S. 1983. Nature and origin of calc-alkaline lamprophyres: minettes, vogesites, kersantites and spessartites. Transaction Royal Society of Edinburgh, Earth Science, 74, pp. 193–227. https://doi.org/10.1017/S0263593300013663
- Rock, N.M.S. 1991. Lamprophyres. Springer Science and Business Media, New York. Originally published by Blackie and Son Ltd, Glasgow, 294 p.
- Ruffman, A. and Greenough, J. 1988. The Weekend Dykes: a newly recognized dyke swarm cutting the Meguma metasediments on the eastern shore of Nova Scotia. Abstract in Maritime Sediments and Atlantic Geology, 24, pp. 209.
- Ruffman, A. and Greenough, J.D. 1990. The Weekend dykes, a newly recognized mafic dyke swarm on the eastern shore of Nova Scotia, Canada. Canadian Journal of Earth Sciences, 27, pp. 644–648. https://doi.org/10.1139/e90-061
- Saunders, A., Norry, M., and Tarney, J. 1991. Fluid influence on the trace element compositions of subduction zone magmas. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 335, pp. 377–392. https://doi.org/10.1098/rsta.1991.0053
- Shellnutt, J.G., and Dostal, J. 2022. Magmatic and inherited zircon ages from a diorite xenolith of the Popes Harbour dyke, Nova Scotia: implications for late Ediacaran arc magmatism in the Avalon terrane of the northern Appalachians. Minerals 2022, 12, Artcile no. 575, 19 pp. https://doi.org/10.3390/min12050575
- Shellnutt, J.G., Owen, J.V., Yeh, M.W., Dostal, J., and Nguyen, D.T. 2019. Long-lived association between Avalonia and the Meguma terrane deduced from zircon geochronology of metasedimentary granulites. Scientific reports, 9, pp. 1–11. https://doi.org/10.1038/s41598-019-40673-9
- Sun, S.S. and McDonough, W.F. 1989. Chemical Isotope systematics of the oceanic basalts: implications for mantle composition and processes. In Magmatism in the ocean basins. Edited by A.D. Saunders and M.J. Norry. Geological Society, London, Special Publications, 42, pp. 313–345. https://doi.org/10.1144/GSL.SP.1989.042.01.19
- Tate, M.C. 1995. The relationship between Late Devonian mafic intrusions and peraluminous granitoid generation in the Meguma Lithotectonic Zone, Nova Scotia, Canada. Unpublished PhD Thesis, Dalhousie University, Halifax, Nova Scotia, 528 p.
- Tate, MC. and Clarke, D.B. 1993. Origin of the Late Devonian Weekend lamprophyric dykes, Meguma Zone, Nova Scotia. Canadian Journal of Earth Sciences, 30, pp. 2295–2304. https://doi.org/10.1139/e93-199
- Tate, M.C., and Clarke, D.B. 1995. Petrogenesis and regional tectonic significance of Late Devonian mafic intrusions in the Meguma Zone, Nova Scotia. Canadian Journal of Earth Sciences, 32, pp. 1883–1898. https://doi.org/10.1139/e95-145
- Tate, M.C., Clarke, D.B., and Heaman, L.M., 1997. Progressive interaction between Late Devonian mafic-intermediate and felsic magmas in the Meguma Zone of Nova Scotia, Canada. Contributions to Mineralogy and Petrology, 126, pp. 401–415. https://doi.org/10.1007/s004100050259
- Taylor, S.R. and McLennan, S.M. 1985. The continental crust: its composition and evolution. Blackwell, Oxford, 312 p.
- van Rooyen, D., Archibald, D.B., White, C.E., Everest, R., Ross, C.G., and Smit, M.A. 2025. New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada: Canadian Journal of Earth Sciences, 62, pp. 484–512. https://doi.org/10.1139/cjes-2024-0024
- Wang, X., Wang, Z., Zhang, W. Ma, L., Chen, W., Cai, Y-C., Foley, S., Wang., C.Y., Li, J., Deng, J., Feng, Y., Zong, K., Hu, Z., and Liu, Y. 2024. Sulfur isotopes of lamprophyres and implications for the control of metasomatized lithospheric mantle on the giant Jiaodong gold deposits, eastern China. Geological Society of America Bulletin, 136, pp. 3405–3418. https://doi.org/10.1130/B37274.1.
- White, C.E. 2010. Stratigraphy of the Lower Paleozoic Goldenville and Halifax groups in the western part of southern Nova Scotia. Atlantic Geology, 46, pp. 136–154. https://doi:10.4138/atlgeol.2010.008.
- White, C.E., Palacios, T., Jensen, S, and Barr, S.M. 2012. Cambrian–Ordovician acritarchs in the Meguma terrane, Nova Scotia, Canada: resolution of Early Paleozoic stratigraphy and implications for paleogeography. Geological Society of America Bulletin, 124, pp. 1773–1792. https://doi.org/10.1130/B30638.1
- Wyman, D. 2025. Lamprophyres, gold and orogenies: a mineral systems perspective. In Alkaline rocks: economic and geodynamic significance through geological time. Edited by R. Pandey, A. Pandey, L. Krmíček, C. Cucciniello, and D. Müller. Geological Society, London, Special Publications, 551, 16 pp. https://doi:10.1144/SP551-2024-53.