Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88 Ga) Kotalahti Nickel Belt, Finland - Implications for crustal contamination at the Archaean/Proterozoic boundary

Abstract

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 ε Nd values at 1880 Ma from -2.4 to +2.0. No relaNo relationship can be found between the degree of Ni mineralization and initial ε Nd values, while a correlation with the geological domain and country rocks is evident. The Majasaari and Törmälä intrusions, which have positive ε Nd values, were emplaced within the Svecofennian domain in proximity to 1.92 Ga tonalitic gneisses, which have previously yielded initial ε Nd values of ca. +3. In contrast, the Luusniemi intrusion, which has an ε Nd value of -2.4 is situated close to exposed Archaean crust. Excluding two analyses from the Rytky intruArchaean crust. Excluding two analyses from the Rytky intru-. Excluding two analyses from the Rytky intrusion, all data from the Koirus N, Koirus S, Kotalahti, Rytky and Kylmälahti intrusions, within error limits, fall in the range -0.7 ± 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 ε Nd values near +4.

Layered Mafic–Ultramafic Intrusions of Fennoscandia: Europe's Treasure Chest of Magmatic Metal Deposits

“…This observation suggests that addition of external, sedimentary-derived sulfur to the magmas triggered early saturation of sulfide melt in the magma. The model is consistent with isotopic and trace element data for several of the Fennoscandian intrusions (Hanski et al 1997;Andersen et al 2006;Makkonen and Huhma 2007;Brownscombe et al 2015).…”

Mafic plutonic rocks in a continental‐arc setting: geochemistry of 1.87–1.78 Ga rocks from south‐central Sweden and models of their palaeotectonic setting

“…Alapieti et al 1990;Amelin and Semeonov 1996;Mutanen 1997;Hanski et al 2005;Makkonen and Huhma 2007), (ii) 1.85-1.65 Ga Transscandinavian Igneous Belt (TIB) intrusions (Andersson 1997b;Claeson 2001;Andersson et al 2006aAndersson et al , 2007, (iii) rapakivi granite-related mafic rocks (e.g. Savolahti 1956;Rämö 1991;Lindh et al 2001a) and (iv) Sveconorwegian mafic complexes (e.g.…”