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Journal of the Geological Society; 2002; v. 159; issue.5; p. 485-488;
DOI: 10.1144/0016-764901-162
© 2002 Geological Society of London

Short Communication

Proterozoic zircon ages from lower crustal granulite xenoliths, Kola Peninsula, Russia: evidence for crustal growth and reworking

H. DOWNES1, P. PELTONEN2, I. MÄNTTÄRI2 & E.V. SHARKOV3

1 1School of Earth Sciences, Birkbeck College, University of London, Malet Street, London, WC1E 7HX, UK (e-mail: h.downes@ucl.ac. uk)
2 2Geological Survey of Finland, PO Box 96, Espoo, FIN-02151 Finland
3 3Institute of Ore Deposits Geology, Petrology, Mineralogy and Geochemistry (IGEM) RAS, Staromonetny per. 35, Moscow, Russia

Lower crustal garnet granulite xenoliths from beneath the Kola–Karelian domain of the Fennoscandian Shield (Russia) were brought to the surface in Devonian lamprophyre diatremes. To establish the relationships between processes in the lower crust and geological events recorded in the upper crust, zircons from two of these xenoliths were dated by ion microprobe. One xenolith contains mainly primary magmatic zircon grains that yielded an average age of 2.47 Ga. The Kola–Karelia domain formed part of a large basaltic igneous province in the earliest Proterozoic (c. 2.45 Ga); thus, such xenoliths probably represent deep-seated equivalents of this magmatism. A second garnet granulite xenolith contained only internally featureless zircons. Most of these yielded concordant ages between 1.77–1.61 Ga. This age distribution indicates that at c. 1.7 Ga the protolith was migmatized during an event that may be related to emplacement of granites and pegmatites in the region. However, two zircon grains in the second xenolith gave much younger ages of 1.47 and 1.45 Ga. This spread in the ages is related to an unknown younger event around 1.4 Ga (or perhaps later) when the c. 1.7 Ga ’migmatite‘ zircons were reset to variable degrees. These zircon ages are evidence for the complex evolution of the lower crust, recording multiple events, some of which are not currently expressed on the surface.


Keywords: Fennoscandian Shield, xenoliths, lower crust, zircon.




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 Geological Society, London, MemoirsHome page
J. S. Daly, V. V. Balagansky, M. J. Timmerman, and M. J. Whitehouse
The Lapland-Kola orogen: Palaeoproterozoic collision and accretion of the northern Fennoscandian lithosphere
Geological Society, London, Memoirs, 2006; 32: 579 - 598.
[Abstract] [PDF]