The structure and cryptic layering of the Pados-Tundra ultramafic complex, Serpentinite belt, Kola Peninsula, Russia

The Paleoproterozoic Pados-Tundra ultramafic complex, ~6 x 1.5-2.1 km in size and ~2.1 Ga in age, located in the Kola Peninsula of Russia, is the main representative of the Serpentinite belt in the northern Fennoscandian Shield. It is composed of fragmented or foliated bodies of dunite-harzburgite-orthopyroxenite; these have an elevated potential for Cr and the platinum-group elements (PGE). In general, the complex consists of the Dunite Zone (olivine cumulates) and Orthopyroxenite Zone (orthopyroxene + olivine cumulates, interlayered); its upper zones of more evolved rocks of mafic compositions appear to have been removed by erosion. The complex shows well-recognized patterns of cryptic layering, documented along cross-sections in grains of olivine and Ca-poor pyroxene. Narrow ranges of high-Mg compositions are observed in olivine [Fo85.5-90.6] and orthopyroxene [Wo