Evolution of the Archaean Karelian Province in the Fennoscandian Shield in the light of U-Pb zircon ages and Sm-Nd and Lu-Hf isotope systematics

• Published in: Journal of the Geological Society
• Main Authors: Lauri, Laura S., Andersen, Tom, Hölttä, Pentti, Huhma, Hannu, Graham, Stuart
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Koillismaa; Fennoscandia; Fennoscandian; karelian
• Online Access: https://researchers.mq.edu.au/en/publications/d723defe-b019-45be-b746-fd870452133b; https://doi.org/10.1144/0016-76492009-159; http://www.scopus.com/inward/record.url?scp=84860389236&partnerID=8YFLogxK

In situ Lu-Hf (laser ablation microprobe-inductively coupled plasma mass spectrometry (LAMICPMS)) and U-Pb (LAM-ICPMS, secondary ionization mass spectrometry (SIMS)) analyses of zircon, and whole-rock Sm-Nd isotope analyses were performed on rocks formed during magmatic events in three Archaean complexes in the Karelian Province of Fennoscandia (Pudasjärvi, Koillismaa and Iisalmi). These complexes have U-Pb ages ranging from 3.5 to 2.6 Ga. In Pudasjärvi, sparse xenocrystic cores give ages of 3.6-3.7 Ga and initial 176 Hf/ 177 Hf suggesting influence of a crustal component T ≥ 4.0 Ga (assuming a CHUR-like mantle source). Ages and Nd and Hf isotope patterns indicate magmatic events at 3.6-3.7 Ga (Siurua, Pudasjärvi with ≥4.0 Ga precursor), 3.2 Ga (Iisalmi, Koillismaa), 2.8 Ga (Pudasjärvi) and 2.7 Ga (Pudasjärvi, Iisalmi). In the Meso- and Palaeoarchaean events, there is no evidence of sources equivalent to present-day depleted mantle; such sources were, however, involved in the 2.8-2.7 Ga events. Hf and Nd are strongly correlated. Contrasts between the Archaean complexes indicate that they evolved separately until c. 2.7 Ga. The age and Hf pattern of ≤2.8 Ga rocks in the Karelian Province is compatible with a scenario in which the Karelia, Superior, Yilgarn and Slave cratons were part of a late Archaean supercontinent, but does not constitute proof of the existence of such a supercontinent.