Distribution of First Row Transition Elements in Eclogites

Surficial materials are recycled back into the deep Earth at subduction zones. The oxidation state of subducted materials affects the oxidation state of major geochemical reservoirs in the Earth, such as the mantle and the crust. First row transition elements (FRTEs), such as V and Sc, are highly redox sensitive and thus have the potential to track important redox processes in subduction zones. In this project, concentrations of FRTEs in garnet, omphacite, and rutile were determined for a global suite of oceanic eclogites, which represent exhumed subducted materials. Data were collected by LA-ICP-MS using an ESI NWR193UC laser ablation system coupled to an Agilent 8900 ICP-MS/MS. Ablation conditions were 12–20 μm spot size at a fluence of ~3 J/cm2 and a repetition rate of 5–8 Hz. Trace element concentrations in garnet and omphacite were determined relative to NIST SRM612, and relative to R10 for rutile. NIST SRM610, GSD-1G, GSE- 1G, and R19 were analyzed as quality control materials. Elements such as V and Cr are preferentially partitioned into rutile over the silicates, whereas Sc, Co, Zn, and Ge are predominantly found in omphacite and garnet. Scandium, Co, and Ga were below detection limit in rutile, and Ni and Ge were only measurable in omphacite and garnet, respectively. Scandium is more compatible in garnet than omphacite. Zinc and Ga are more compatible in omphacite than garnet. Omphacite/garnet partition coefficients for Co are close to one