Figure 3: Evolved Parana and Etendeka continental flood volcanism shows much greater isotopic variation than the oceanic Tristan-Gough hotspot track lavas.
From: How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot
On plots of MgO vs. (a) 87Sr/86Sr and (b) 143Nd/144Nd, the oceanic lavas have relatively constant composition and unradiogenic 87Sr/86Sr but radiogenic 143Nd/144Nd regardless of MgO content (degree of differentiation). The continental volcanism, however, shows a greater range in 87Sr/86Sr and 143Nd/144Nd extending to systematically more radiogenic 87Sr/86Sr and less radiogenic 143Nd/144Nd with increasing degree of differentiation (decreasing MgO). The increasing and substantially greater range in 87Sr/86Sr and 143Nd/144Nd for the continental, compared with oceanic, volcanic rocks primarily reflects increasing amounts of assimilation during fractional crystallization of continental lithosphere by some magmas. Radiogenic ingrowth in some of the most evolved silica-saturated samples with very high Rb/Sr ratios also contributes to the extremely radiogenic 87Sr/86Sr. Average correction for radiogenic ingrowth for Parana and Etendeka is based on 498 (87Sr/86Sr) and 280 (143Nd/144Nd) analyses for which parent/daughter ratios are available. See Supplementary Dataset 5 and additional data from GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).
