Small length scale heterogeneity beneath the East Pacific Rise

Samples from ~1.80°N show a relatively large range in trace element abundances (Ba/Zr = 0.110.80, Ce/Yb = 2.64-7.77) and isotope ratios (87Sr/86Sr = 0.70226-0.70282, 143Nd/144Nd = 0.5130700.513275, 176Hf/177Hf = 0.283105-0.283281, 206Pb/204Pb = 17.54-18.62) encompassing ~70% of the variability displayed by EPR ridge basalts even though they are collected from 2 higher than most EPR basalts but with 87Sr/86Sr and 143Nd/144Nd similar to EPR basalts. The other end of the spectrum has trace elements characteristics similar to EPR basalts but is more depleted in isotopic compositions. They are similar to the Garrett transform lavas. The degree of isotopic variation observed along this 25km ridge segments is similar in amplitude as observed in EPR seamounts. The large variation in a small area indicates the presence of significant small-scale heterogeneities in the sub-ridge mantle. The ridge basalts average melt from a smaller area of a mantle than the proposed length scale of melting (100km) and points at efficient melt extraction and inefficient mixing of melts.