Discussion
Higher ratios of 87Sr/86Sr and lower values of epsilon Nd (εNd) are observed in continental flood basalts because of :
Answer: D
The signature comes from Assimilation of continental crust.
Continental crust has high Rb/Sr and low Sm/Nd ratios, so over time it develops high 87Sr/86Sr and strongly negative εNd. When mantle-derived basalt melts and assimilates such crust on its way up, the magma inherits both features, which is why many continental flood basalts, including parts of the Deccan, show them.
A deeper mantle source or entrained mantle material would give mantle-like values (lower Sr ratio, positive εNd), and the degree of partial melting changes trace element concentrations but not isotope ratios.
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