Sm‐Nd isotope data from the Halti‐Ridnitsohkka mafic‐ultramafic complex in the northern Scandinavian Caledonides

Abstract

Samples from the Halti‐Ridnitsohkka mafic‐ultramafic complex in the northern part of the Scandinavian Caledonides have been studied by the Sm‐Nd isotope dating method. Three samples from the Haiti cumulate sequence (olivine gabbro) gave an age of 564±35 Ma and an initial eNd of 5.7±0.3(theinitial143Nd/144Ndratiois0.51220±6). The magma source is a depleted mantle. Five samples from the Ridnitsohkka gabbro dolente dyke swarm yield data that are too scattered to give any acceptable isochron and age for this unit. There is a significant difference in the amount of Nd in the samples between these two units.The Ridnitsohkka dyke complex is separated from the Haiti cumulates by a shear zone of unclear significance. Previous work on badelleyite and zircon from the Ridnitsohkka dyke complex has yielded Ordovician ages (425–445 Ma). It has not been possible to evaluate the apparent conflict in these results. However, the conclusion here is to place the Halti‐Ridnitsohkka mafic‐ultramafic complex in the Kalak Nappe Complex of the Middle Allochthon and not as an eastern component of the Reisa Nappe Complex of the Upper Allochthon. Matsson, I., 1994; Sm‐Nd isotope data from the Halti‐Ridnitsohkkamafic‐ultramafic complex in the northern Scandinavian Caledonides. GFF, Vol. 116 (Pt. 1, March), pp. 13–16. Stockholm. ISSN 1103–5897.