The Paleoproterozoic Otish Gabbro suite and coeval dyke swarms of the Superior Province: Probing the ca. 2.17Â Ga mantle

The Otish Gabbro sills are part of a large ca. 2.17 Ga magmatic event that also generated the extensive Biscotasing and Payne River dyke swarms in the south-central and northeastern Superior Province, respectively. The contemporaneous mafic dyke swarms experienced relatively minor crustal contamination and their high Nb/Zr and Nb/Yb ratios suggest derivation from fertile mantle sources. Furthermore, the low Ti/Yb ratios of the ca. 2.17 Ga magmas are consistent with melting at relatively shallow depths (<100 km), implying removal of the depleted Archean lithosphere from a large portion of the Superior Province and replacement by a more fertile Proterozoic mantle. The variable geochemical composition of the ca. 2.17 Ga mafic magmas indicates melting of a compositionally heterogeneous mantle and appears inconsistent with a common distal mantle plume source. A more suitable petrogenetic model for the ca. 2.17 Ga dyke swarms of the Superior Province is vertical rise of mantle-derived magmas in a rifting environment.