Constraints on diamond formation and craton evolution from S isotopes and trace element contents in diamond sulfides

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Diamonds are rare accessory mantle minerals sampling deep mantle lithologies including cratonic eclogites. These are indicative of major processes affecting lithosphere evolution, i.e. whether they were emplaced via subduction of oceanic crust or crystallized from mafic melts within the mantle. Diamond dating studies have revealed many eclogitic diamond suites to be ancient (Proterozoic or Archaean). This, combined with the chemically inert nature of diamond, which prevents its mineral content from being modified by post-formation mantle metasomatic events, makes the study of inclusions in diamonds particularly exciting. Since sulfide minerals are a frequent inclusion type in diamonds that contain high abundances of chalcophile and siderophile elements in addition to sulfur, they lend themselves to in situ analytical techniques. Eclogitic sulfide inclusions, isolated from diamonds sampling the deep lithosphere in the central Slave Craton, have previously been dated to ca 1.9 Ga, a time corresponding to subduction at the Slave craton margin, but also close to a major dike formation episode leading to the crystallization of mafic components in the mantle. I propose to determine multiple S isotopes on sulfide inclusions by ion microprobe to constrain a crustal vs deep formation origin (S isotopes can be fractionated in the shallow lithosphere including the oceanic slab but not in the deep mantle). Additional investigation of the trace-element abundances, which are fractionated during fluid release and partial melting, by laser ablation ICPMS, promises insights on the origin of the sulfides, conditions of diamond formation and evolution of the associated lithospheric mantle.