The early tectono-magmatic evolution of the Southern Province: implications from the Agnew Intrusion, central Ontario, Canada

The Palaeoproterozoic Southern Province comprises a thick, continental rift related volcanic-sedimentary sequence along the southern margin of the Archaean Superior Province. The Agnew Intrusion (50 km2), which is a member of the East Bull Lake suite of layered intrusions, occurs adjacent to the Superior Province - Southern Province boundary in central Ontario, Canada, and provides an opportunity to examine the early tectono-magmatic evolution of a Palaeoproterozoic rifting event. The Agnew Intrusion is a well-exposed, 2100 m thick, layered gabbronoritic to leucogabbronoritic pluton. It was the product of at least four recognizable, but chemically similar, high-Al2O3 and low-TiO2 magma pulses. Structural data, coupled with excellent stratigraphic correlations between the Agnew Intrusion and other East Bull Lake suite layered intrusions, suggest that these plutons are erosional remnants of one or more sill-like bodies that may originally have formed an extensive, subhorizontal mafic sheet. We argue on the ...