Abstract
143Nd/ 144Nd ratios have been determined on Recent basic volcanics from two areas of continental volcanism, Roccamonfina in the Roman Province of Italy and Mt. Etna in Sicily. The 143Nd/ 144Nd ratios of Mt. Etna volcanics range from0.51292 ± 3to0.51298 ± 2 and are similar to Icelandic and other oceanic volcanics. In contrast the 143Nd/ 144Nd ratios of Roccamonfina volcanics range from0.51208 ± 2to0.51240 ± 2 and are the lowest yet recorded in Recent volcanics. These data together with 87Sr/ 86Sr ratios extend the range of covariation of Nd- and Sr-isotope compositions in basaltic rocks. Relative to average chondrite REE abundances, the Mt. Etna volcanics have been derived from sources with a time-integrated light-REE depletion, whereas the source regions of the Roccamonfina volcanics have a time-integrated light-REE enrichment. The light-REE-depleted character implied by the Nd-isotope data for the sources of the Mt. Etna tholeiites is in direct contrast with the light-REE enrichment in the tholeiites themselves. This discrepancy is most simply resolved by postulating an enrichment event in the source regions of the Mt. Etna tholeiites ca. 2−5 × 10 8 years ago. This event occurred sufficiently close in time to the present that the current light-REE-enriched character of the sources is not reflected in its Nd-isotope composition.
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