The early Nd and Hf isotope data correlated well with 87Sr/86Sr and appeared to terminate at εNd = 0 and εHf = 0, forming the mantle array in Figure 3.1. This seemed consistent with the idea that the mantle sources of oceanic basalts were mixtures of two components: a depleted reservoir (MORB source) and a primitive, or possibly enriched, reservoir. However, even some of the earliest published Sr and Pb isotope data suggested the situation was more complicated. Along the northern Mid-Atlantic Ridge, 87Sr/86Sr and 206Pb/204Pb were correlated...

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