Comparing multiple oxybarometers preserved in igneous zircon

Magma redox conditions exert a significant control on Fe-bearing mineral constituents, including oxide phase stability. Given the increasing use of detrital zircon as not only provenance indicator but also for reconstructing magmatic arcs, we investigated whether the cerium anomaly (Ce/Ce*) in zircon is a good predictor of oxide phases present as primary inclusions in zircon, as well as oxides present in the rock matrix. Zircon Ce/Ce*-based redox estimates often show a wide range in individual granitoids and some ambiguities arise when applying it to detrital suites (e.g., correcting TiO₂ activity for calculation of Ti temperatures). We separated zircon and opaque oxides from a suite of North American granitoids across the compositional range and identified primary mineral inclusions using energy-dispersive X-ray analysis. We also determined Ce/Ce* and Ti temperatures using the CAMECA ims1270 ion microprobe. Oxide inclusions in zircon are rare in felsic granitoids but often constitute >5% of the zircon inclusion assemblage in intermediate granitoids. The same oxide phases present in the matrix exist as inclusions in zircon, although the relative phase proportions differ in many cases. However, Ce/Ce* varies systematically with the proportion of ilmenite among the Fe-Ti oxide inclusions, suggesting a faithful recording of magma redox during the period of zircon crystallization. Joint use of Ce/Ce* oxybarometry and the oxide inclusion composition in zircon appears to provide the most robust estimate for the magma redox states of weathered or metamorphosed granitoids and for the protoliths of detrital suites, although it is not clear how well they predict the final proportion of oxides in the granitoid matrix.