Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability

Pyroxenites embedded in peridotite are often invoked as a major cause of short-length\udscale isotopic heterogeneities in the upper mantle, but there has been little direct evidence.\udWe report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and\udtheir host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy,\udwith depleted mantle compositions, representing a surface exposure of veined upper mantle, a\udpotential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and\udadjacent mantle rocks results in centimeter-scale chemical modifi cations in the host peridotites,\udsystematically lowering their Sm/Nd ratios. Over time, this interaction causes the host\udperidotite at >0.1 m scale to acquire an isotopic heterogeneity larger than the range defi ned\udby the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single\udoutcrop covers most of the global Nd isotopic variability documented in abyssal peridotites.\udSuch pyroxenite-peridotite veined mantle domains may represent the enriched component\udrarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd\udvariations in MORB