The geochemistry and petrogenesis of the early Proterozoic Matachewan Large Igneous Province

Doctoral thesis English OPEN
Ciborowski, Thomas
  • Subject: QE

The Matachewan Large Igneous Province (LIP) is interpreted to have formed during mantle plume-induced continental break-up during the early Proterozoic. When the Matachewan LIP is reconstructed to its original configuration, the dyke swarms,layered intrusions and flood basalt provinces emplaced over the lifetime of the province comprise one of the largest magmatic provinces recognised in the geological record. New geochemical data allow, for the first time, the Matachewan LIP to be treated as a single, coherent entity.\ud The major and trace element data presented here show that Matachewan LIP suites share a common tholeiitic composition and trace element geochemistry characterised by enrichment in the most incompatible elements and depletion in the less\ud incompatible elements. This signature, ubiquitous in early Proterozoic continental magmatic rocks, may indicate that the Matachewan LIP formed through contamination or mixing of its primary magmas with crustal material or that the early Proterozoic mantle had a fundamentally different composition to the modern mantle.\ud Aside from the radiating geometry of the dyke swarms, a plume origin for the Matachewan LIP is implied by the geochemistry of some of the suites, used here to constrain the potential temperature of the magmatism. Comparison of these potential temperatures with the temperature of the early Proterozoic upper mantle, shows that the province is the product of anomalously hot magmatism as predicted by mantle plume theory. Geochemical data from coeval intrusions suggest that the plume head was compositionally heterogeneous and sampled material from both depleted and enriched mantle. Sr-Nd-Pb isotopic data show that this source heterogeneity dictates the Ni-Cu-PGE potential of the related intrusions.\ud The enormity of the Matachewan LIP cannot be overstated and its potential impact on the early Proterozoic global environment was likely immense – it may even have been the trigger to the irreversible oxygenation of our planet.
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