Tracking fluid/melt flow in lower crustal mafic gneiss using zircon isotopic zoning, kapuskasing uplift

Coordinated cathodoluminescence (CL) imaging and ion microprobe (SHRIMP and CAMECA 1280) analysis (U-Pb dating, oxygen isotope and trace element) of metamorphic zircon from a granulite-facies mafic orthogneiss in the Kapuskasing Uplift of the Archean Superior Province reveal episodes of fluid-rock interaction. Metamorphic zircon grains were isolated from six sample sites along a 10 m traverse away from contact with a high ?18O paragneiss unit. CL images reveal that most zircons have bright cores surrounded by darker rims. The 207Pb/206Pb ages of metamorphic zircons generally range from 2660 to 2550 Ma. Age differences between cores and rims are not always resolvable within the analytical precision of SHRIMP measurements (± 8 to 247 Ma, 2sd) due to very low U concentrations in many zircon cores. Ages do not vary systematically with distance across the traverse.