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The Shuram–Wonoka event recorded in a high-grade metamorphic terrane: insight from the Scandinavian Caledonides

V. A. MELEZHIK^*,, D. ROBERTS^*, A. E. FALLICK and I. M. GOROKHOV

^* Geological Survey of Norway, N-7491 Trondheim, Norway
Scottish Universities Environmental Research Centre, G75 0QF East Kilbride, Glasgow, Scotland, UK
Institute of Precambrian Geology and Geochronology, nab. Makarova, 2, 199034 St Petersburg, Russia

Author for correspondence: victor.melezhik{at}ngu.no

An approximately 250 m thick polydeformed and polymetamorphosed, isotopically unusual, variegated marble (locally termed the ‘Leivset marble’) shows a great lateral extent in the Scandinavian Caledonides. Its extremely ¹³C-depleted primary nature (–7.9 ± 1.2 on average, n = 93) makes the Leivset marble unique. This, together with a high Sr content (up to 8740 ppm) that buffered ⁸⁷Sr/⁸⁶Sr ratios between 0.70802 and 0.70872, suggests correlation with the worldwide Shuram–Wonoka isotopic event occurring within the 600–550 Ma time interval during the Ediacaran (Vendian) period. Despite a high-grade deformation and metamorphism, the Leivset marble has retained its original carbon and strontium isotope ratios. A combination of the variegated colour with unusually low ¹³C_carb can potentially be used for stratigraphic correlations in high-grade, non-fossiliferous, marble-dominated terranes across the Caledonian orogenic belt in Baltica and Laurentia. Isotope chemostratigraphy has identified a prominent cryptic stratigraphic discontinuity and suggests that the Ediacaran Leivset marble was tectonically juxtaposed above low-grade, Llandovery-age, fossiliferous marbles during the Scandian orogeny.

Key Words: Caledonides • Ediacaran • marble • carbon • strontium • isotopes

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