An enriched mantle source for Italy's melilitite-carbonatite association as inferred by its Nd-Sr isotope signature

New Sr-Nd isotope data were obtained from Late Pleistocene carbonatite-kama fugite associations from the Umbria-Latium Ultra-Alkaline District of Italy (ULUD) with the aim of constraining their origin and possible mantle sourc e(s). This is relevant to the origin and evolution of ultrapotassic (K/Na > >2) and associated locks generally, notably the occurrences from Ugandan ka mafugites, Western Australian lamproites and South African orangeites. The selected ULUD samples yielded Sr-87/Sr-86 and Nd-143/Nd-144 ranging from 0. 7100 to 0.7112 and from 0.5119 to 0.5121 respectively, similar to cratonic potassic volcanic rocks with higher Rb/Sr and lower Sm/Nd ratios than Bulk Earth. Silicate and carbonate fractions separated from melilitite are in is otopic equilibrium, supporting the view that they are cogenetic. The ULUD c arbonatites yielded the highest radiogenic Sr so far reported for carbonati tes. In contrast, sedimentary limestones from ULUD basement formations are lower in radiogenic Sr, i.e. Sr-87/Sr-86 = 0.70745-0.70735. The variation t rend of ULUD isotopic compositions is similar to that reported for Ugandan kamafugites and Western Australian lamproites and overlaps the values for S outh African orangeites in the epsilon(Sr)-epsilon(Nd) diagram. A poor corr elation between Sr\Nd and Sr-87/Sr-86 ratios in ULUD rocks is inconsistent with a mantle source generated by subduction-driven processes, while the ne gligible Sr and LREE in sedimentary limestones from the ULUD region fail to account for a hypothetical limestone assimilation process. The Nd model ag es of 1.5-1.9 Ga have been inferred for a possible metasomatic event, allow ing further radiogenic evolution of the source, a process which may have oc curred in isolation until eruption time. While the origin of this component remains speculative, the Sr-NJ isotope trend is consistent with a simple m ixing process involving an OIB-type mantle and a component with low epsilon (Nd) and high epsilon(Sr).