Evidence Of Magmatism And Rifting In The Southern Superior Craton From The Temagami Geophysical Anomaly

The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supergroup near the southern margin of Archean Superior craton, along strike from the Temagami Greenstone Belt, 50 km northeast of world-class metal endowment in the Sudbury Igneous Complex. It has been attributed to coincidental geophysical responses from Neoarchean iron formation and a Paleoproterozoic mafic-ultramafic intrusion. The TGA is investigated using integrated magnetotelluric, magnetic, gravity and seismic reflection datasets to further define the geometry of its sources; to define structures in overlying Huronian Supergroup rocks; and to examine the geometrical relationship of Archean basement structure, the Proterozoic mafic-ultramafic intrusion, and Proterozoic rift structures.Geophysical results reveal a strong conductor, interpreted to be iron formation, extending downwards from the Archean basement surface and enveloping the upper northern margin of a large magnetic, dense body at 5 km depth. The geometry of the features indicates mafic-ultramafic intrusion adjacent to greenstone rocks. Alignment of the long-axis of the intrusion with the greenstone belt suggests control on the intrusion process by the Neoarchean structures. The 60x10x10 km TGA intrusion lies within the mantle-plume, rift-related Huron-Nipissing magmatic belt and interpreted to be a member of the 2.491-2.475 Ga East Bull Lake intrusive suite. Based on this genetic relationship, the intrusion probably contributes significantly to Ni-Cu-PGE endowment of the Sudbury region. The spatial correlation of the intrusion with an overlying 20 km wide, 4.5 km deep, fault-bounded rift basin is attributed to crustal subsidence triggered by the intrusion. Seismic reflection and magnetotelluric results show younger Huronian Supergroup rocks record the transition to sedimentation on a laterally-extensive passive margin. An electrically-anisotropic, moderately-conductive layer in the Gowganda Formation is related to alteration during intrusion of the 2.200 Nipissing Diabase.