The 1.75-Ga Iron King Volcanics in west-central Arizona: a remnant of an accreted oceanic plateau derived from a mantle plume with a deep depleted component

Abstract

Two lithologic assemblages are recognized in the 1.75-Ga Iron King Volcanics in west-central Arizona: an arc assemblage composed of pillow basalts, intermediate and felsic volcanics and associated volcaniclastic sediment, and an oceanic plateau assemblage composed chiefly of pillow basalts and mafic hyaloclastic breccia. During collision of the Iron King oceanic plateau with Laurentia 1.7 Ga, plateau and arc components were tectonically interleaved. Iron King arc volcanics have subduction-related geochemical signatures with affinities to continental margin arcs. The Iron King plateau basalts include two groups: enriched and nonenriched in very incompatible elements. The enriched group may reflect smaller degrees of melting in the outer, cooler part of a plume head. Incompatible element distributions indicate that the plateau basalts came from a mantle source with mixed depleted and recycled components and a small contribution of an enriched component. Nb/Y–Zr/Y relationships suggest the depleted component came from the deep mantle, rather than being entrained at shallow depths. Our results suggest that recycled, depleted and enriched components were available in the deep mantle by 1.75 Ga.