Sequential siliciclastic and carbonate metasomatism revealed by potassium and magnesium isotopic decoupling in Wyoming lamproites

Cratonic lamproites commonly exhibit extreme Sr-Nd-Pb isotopic compositions characteristic of enriched mantle I (EMI), yet the relative roles of recycled siliciclastic and carbonate materials in generating EMI-like mantle sources remain debated. Here we show K isotopic variations in lamproites from Leucite Hills, Wyoming, and integrate them with previously published Mg-Sr-Nd-Pb isotopic data to constrain metasomatic processes in their mantle sources. Phlogopite lamproites have low δ41K but mantle-like δ26Mg values and display more extreme EMI-like Sr-Nd-Pb isotopic signatures, whereas madupitic lamproites have low δ26Mg but largely mantle-like δ41K values and less extreme EMI-like Sr-Nd-Pb isotopic signatures. These relationships are consistent with a two-stage metasomatic history in which an ancient siliciclastic sediment-related event established the light K and EMI-like Sr-Nd-Pb isotopic signatures, followed by a younger carbonate-related event that introduced the light Mg isotopic signature while overprinting the earlier source. Potassium isotopes thus provide a sensitive tracer of sediment-driven metasomatism and, combined with Mg and radiogenic isotopes, help resolve multistage mantle metasomatism. The potassium and magnesium isotope patterns suggest that the Wyoming craton mantle was influenced by at least two separate episodes of metasomatism involving different recycled materials, according to geochemical analysis of the Leucite Hills lamproites from the Wyoming craton.