Geochemical evidence for a widespread mantle re-enrichment 3.2 billion years ago: implications for global-scale plate tectonics

摘要

Nd/ Nd ratio (represented as εNd) vs. age plot for Archaean and Proterozoic basaltic rocks and komatiites (data from Spencer . . Brown circles represent individual samples. Red dots represent the median of samples with the same age, and the associated error bars spans across the middle 50% of the data, called the median data range here. The red field represents the envelope for the median range. The large variation in the mean εNd values after ~3.2–3.0 Ga suggests an isotopic shift in the mantle source of the basaltic rocks and the komatiites. The depleted mantle curves are shown for comparison .