Nd and Sr isotopic studies on cenozoic mafic lavas from West Antarctica: Another source for continental alkali basalts

The Nd and Sr isotopic ratios on a suite of continental alkali basalts from Marie Byrd Land, West Antarctica, define a change in the source over the range of K/Ar dates between 1 and 28 m.y. ago. The ⁸⁷Sr/⁸⁶Sr isotopic ratios (0.7026 to 0.7031) are unusually low for continental alkali basalts, although the corresponding ¹⁴³Nd/¹⁴⁴Nd ratios (0.51283 to 0.51299) are similar to previously reported values. On a ⁸⁷Sr/⁸⁶Sr vs. ¹⁴³Nd/¹⁴⁴Nd diagram, they define a trend on the low ⁸⁷Sr/⁸⁶Sr side of the “mantle array”, which has a slope steeper than the mantle array. An explanation for the light rare earth elements (LREE) enrichment of the alkali basalts, with high ¹⁴³Nd/¹⁴⁴Nd ratios and low ⁸⁷Sr/⁸⁶Sr ratios, is suggested by a model which modifies the source region with a mantle-derived, CO₂-enriched metasomatic fluid.