Aviat diamonds: a window into the deep lithospheric mantle beneath the northern Churchill Province, Melville Peninsula, Canada

Diamonds from Aviat, on the Melville Peninsula, Canada, display a range in δ ¹³C from -30‰ to -2‰, with a prominent mode at -5‰. Strongly 13C-depleted diamonds indicate derivation from eclogitic sources and are likely related to precipitation from remobilized, subducted former organic matter. The main population of diamonds around -5‰ may be of eclogitic or peridotitic derivation. Complex CL patterns and abrupt variations in carbon isotopic composition (δ ¹³C) indicate that at least three episodes of diamond growth occurred, separated by periods of resorption. Nitrogen concentration and δ ¹³C are decoupled both on the level of individual growth-zones and for the bulk diamond data, indicating that either multiple sources of fluid contributed to diamond formation at Aviat or that nitrogen was fractionated through partitioning into potassium-bearing minerals. Nitrogen-based mantle-residence temperatures for Aviat diamonds mostly fall in the range ∼1050-1150 °C; projected on a syneruptive paleogeotherm of 38 mW/m ² surface heat-flow, this indicates sampling over a narrow interval between ∼150-170 km depth.