230Th-238U disequilibrium in East Scotia backarc basalts: Implications for slab contributions

New U-series isotope data for lavas from the East Scotia backarc spreading center span a large range in (230Th/232Th) and (238U/232Th). Most of the backarc lavas have (238U/230Th) 1 and are enriched in fluid-mobile elements, implying a recent addition of a U-rich slab-derived component. The data from one segment suggest an influence from an aqueous fluid from altered MORB, whereas samples from the other slab-influenced segment show addition of a sediment melt. The slab-influenced samples form a distinct trend in the equiline diagram between aqueous fluid and sediment melt that is suggested to be a mixing line rather than an isochron.

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