Trace element and C–O–Sr–Nd isotope evidence for subduction-related carbonate–silicate melts in mantle xenoliths (Pannonian Basin, Hungary)

Abstract

Carbonate globules have been found in amphibole-bearing glass veins of peridotite xenoliths from Szentbékálla (Balaton Highland, Central Hungary). Strong resorption of amphibole suggests multiple fluid-melt infiltration. Textural features of carbonate globules and the surrounding silicate glass indicate a magmatic melt origin for the carbonate and exclude the possibility of significant alteration. The application of the cpx structural barometer for clinopyroxenes formed in the silicate glass indicates high-pressure vein formation. Laser-ablation ICP-MS analyses revealed trace element zoning within the carbonate. Uniform profiles observed for various elements within the carbonate indicate that the zoning is related to non-diffusive mixing during carbonate–silicate interaction rather than to element diffusion. The trace element composition of the centers of the globules (e.g. low Ce/Pb and Nd/Pb ratios) suggests a crustal origin for the carbonate melt. The C, O, and Sr isotope compositions of the calcite globules ( δ 13C about −14‰; δ 18O about 22‰; 87Sr/ 86Sr=0.70533) also argue for a crustal origin of the carbonate melt. Trace element and C–O–Sr isotopic compositions of calcite globules suggest that the carbonate melt was derived from subducted material. Injection of the carbonate melt into the peridotite triggered amphibole melting. The carbonate and silicate melts intermingled, but their interaction was confined to the margins of carbonate globules. Preservation of trace element zoning and element diffusion calculations indicate that the vein-hosting peridotite was rapidly brought to the surface after the carbonate melt injection.