The Origin of Ultramafic Complexes with Melilitolites and Carbonatites: A Petrological Comparison of the Gardiner (E Greenland) and Kovdor (Russia) Intrusions.

This article focuses on the contrasting petrogenesis of ultramafic rocks associated with alkaline complexes, specifically comparing the Gardiner Complex (East Greenland) and the Kovdor Complex (Russia). It presents evidence that ultramafic rocks in such complexes can form either as magmatic cumulates from mantle-derived silicate melts, as seen at Gardiner, or by metasomatic interaction between mantle-derived carbonatite magmas and crustal host rocks, as observed at Kovdor. These differing origins influence the mineral chemistry, textures, and high field strength element (HFSE) enrichment patterns, with Gardiner showing early HFSE enrichment in silicate phases like perovskite, while Kovdor exhibits HFSE enrichment primarily in carbonatites and phoscorites. The study highlights the importance of distinguishing magmatic versus metasomatic ultramafic rocks for understanding mantle source characteristics and for guiding exploration of economically critical HFSE deposits in alkaline complexes.