We compiled a global database of abyssal peridotite compositions.
Melting indicators in MORB and abyssal peridotites are correlated.
High Na90, low Fe90 in MORB, low Cr# in peridotites from very slow-spreading ridges.
Spreading rate may control how mantle lithologies are sampled during melting.
Alternatively, spreading rate controls mantle temperature at low spreading rates.