Abstract

Diamonds from Aviat, on the Melville Peninsula, Canada, display a range in δ13C 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 (δ13C) indicate that at least three episodes of diamond growth occurred, separated by periods of resorption. Nitrogen concentration and δ13C 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 ºC; projected on a syneruptive paleogeotherm of 38 mW/m2 surface heat-flow, this indicates sampling over a narrow interval between ~150–170 km depth.

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