%0 Journal Article
%T Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88 Ga) Kotalahti Nickel Belt, Finland ¨C implications for crustal contamination at the Archaean/Proterozoic boundary
%A Hannu V. Makkonen
%A Hannu Huhma
%J Bulletin of the Geological Society of Finland
%D 2007
%I The Geological Society of Finland
%X Sm-Nd data were determined for eight mafic-ultramafic intrusions from the Svecofennian (1.88 Ga) Kotalahti Nickel Belt, Finland. The intrusions represent both mineralized and barren types and are located at varying distances from the Archaean/Proterozoic boundary.The samples for the 23 Sm-Nd isotope analyses were taken mostly from the ultramafic differentiates. Results show a range in initial ¦ÅNd values at 1880 Ma from -2.4 to +2.0. No relationship can be found between the degree of Ni mineralization and initial ¦ÅNd values, whilea correlation with the geological domain and country rocks is evident. The Majasaari and T rm l  intrusions, which have positive ¦ÅNd values, were emplaced within the Svecofennian domain in proximity to 1.92 Ga tonalitic gneisses, which have previously yielded initial¦ÅNd values of ca. +3. In contrast, the Luusniemi intrusion, which has an ¦ÅNd value of -2.4 is situated close to exposed Archaean crust. Excluding two analyses from the Rytky intrusion, all data from the Koirus N, Koirus S, Kotalahti, Rytky and Kylm lahti intrusions, withinerror limits, fall in the range -0.7 ¡À 0.3. The results support the concept of contamination by Archaean material in proximity to the currently exposed craton margin. The composition of the proposed parental magma for the intrusions is close to EMORB, with initial¦ÅNd values near +4.
%K intrusions
%K ultramafics
%K gabbros
%K nickel ores
%K geochemistry
%K Sm/Nd
%K magma contamination
%K tectonics
%K Proterozoic
%K Kotalahti
%K Finland
%U http://www.geologinenseura.fi/bulletin/Volume79/Makkonen_Huhma_2007.pdf