THE GEOCHEMISTRY AND PETROGENESIS OF THE MATACHEWAN LARGE IGNEOUS PROVINCE

Our synthesis of available geochemical data allows the Matachewan LIP to be treated as a single, coherent entity. We show that Matachewan LIP suites share a common tholeiitic composition and trace element geochemistry which is characterised by enrichment in the most incompatible elements and depletions in the more compatible, high field strength elements. This signature, common in early Proterozoic continental magmatic rocks, may indicate that the Matachewan LIP formed through contamination of its primary magmas with crustal material or, that the early Proterozoic mantle had a fundamentally different composition to the modern mantle.

Aside from the radiating geometry of the dyke swarms, a plume origin for the Matachewan LIP is consistent with the geochemistry of some of the suites, and these suites are used to constrain the mantle potential temperature of the magmatism. Comparisons of these mantle potential temperatures, which range between c. 1500-1550 ºC, with calculated temperatures of the early Proterozoic upper mantle show that the province is likely formed by melting of a hot mantle plume. Rb-Sr, Sm-Nd and Hf-Lu isotopic data from coeval intrusions suggest that the plume head was compositionally heterogeneous, and that this heterogeneity in source composition may have been a deciding factor in determining the economic potential of the intrusions.