Geochemistry of the mafic and felsic norite in the Whistle Embayment: Implications for the crystallization history of the Sudbury Igneous Complex, Sudbury, Ontario

The ore deposits of the 1.85 Ga Sudbury Structure collectively make up one of the largest Ni-Cu-PGE producing districts in the world.; The evolution of the Sudbury Igneous Complex (SIC) was modeled using the MELTS program and several geologically reasonable initial compositions, including quartz-rich norite, average offset quartz diorite, and average SIC. The average SIC composition, which is very similar to the average offset quartz diorite compositions, appears to be the best estimate of the initial magma composition, providing the best fit to the volumes and cumulus mineralogy of each of the units within the SIC. The MELTS models suggest that the mafic norite, norite, and quartz gabbro are cumulates, whereas the granophyre appears to represent a residual liquid that crystallized downward from the roof. The composition of the norite in the lower portion of the SIC appears to match the composition of the cumulate rocks produced in an equilibrium crystallization model, whereas the compositions of the quartz gabbro and granophyre appear to match the compositions of the cumulate rocks and residual liquids produced in a fractional crystallization model. This suggests that the style of crystallization may have changed from dominantly equilibrium crystallization to dominantly fractional crystallization during the crystallization history of the SIC. (Abstract shortened by UMI.)...