Oxidation state of the lithospheric mantle beneath Diavik diamond mine, central Slave craton, NWT, Canada

摘要: Oxygen fugacity (fO2) conditions were determined for 29 peridotite xenoliths from the A154-North and A154-South kimberlites of Diavik diamond mine using newly developed flank method modified specifically measuring Fe3+ in mantle-derived pyropic garnets. The results indicate that garnet-bearing lithospheric mantle beneath central Slave craton is vertically layered with respect to oxidation state. shallow (<140 km), “ultra-depleted” layer most oxidized section subcratonic thus far measured, up one log unit more oxidizing relative FMQ buffer [Δlog fO2 (FMQ) + 1]. lower, fertile has extend down Δlog − 3.8, consistent xenolith suites other localities worldwide. Based on trace element concentrations garnets, two distinct metasomatic events affected lithosphere at Diavik. An fluid imparted sinusoidal chondrite-normalized REE patterns garnets throughout entire depth range sampled. In contrast, a reducing melt event only lower portion mantle. state sample suggests formation occurred by reduction carbonate fluids arising lithosphere.