CORUNDUM GENESIS IN ALUMINOUS LEUCOSOME AT THE BLUE JAY SAPPHIRE OCCURRENCE (BRITISH COLUMBIA, CANADA) AS A RECORD OF METAMORPHISM AND PARTIAL MELTING IN THE MONASHEE COMPLEX

The aluminous leucosome-hosted sapphire (corundum) occurrence near Revelstoke, British Columbia, Canada, occurs in the Monashee Complex of the Omineca Belt of the Canadian Cordillera. Corundum occurs in banded or pod-like shapes within a leucosome containing muscovite + biotite + albite + orthoclase + garnet ± zircon ± sillimanite ± ilmenite ± monazite ± rutile ± spinel ± titanite. Whole rock geochemistry and petrological observations show that the leucosomes attained crystal-melt equilibrium between melts with high SiO₂, K₂O, and CaO compositions and peritectic plagioclase, corundum, and garnet, with additional silica melt later removed from the system. Petrography and thermodynamic modeling of the corundum-bearing pods show that corundum formed from muscovite dehydration melting at the peak of metamorphism at 800-850 °C and 8-10 kbar. Zircon geochronology in the U/Pb system shows that partial melting occurred during the final stages of prograde metamorphism and that melting was continuous from ~60–50 Ma.