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 delta C-13 from -30 parts per thousand to -2 parts per thousand, with a prominent mode at -5 parts per thousand. Strongly C-13-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 parts per thousand may be of eclogitic or peridotitic derivation. Complex CL patterns and abrupt variations in carbon isotopic composition (delta C-13) indicate that at least three episodes of diamond growth occurred, separated by periods of resorption. Nitrogen concentration and delta C-13 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 similar to 1050-1150 degrees C; projected on a syneruptive paleogeotherm of 38 mW/m(2) surface heat-flow, this indicates sampling over a narrow interval between similar to 150-170 km depth.