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143Nd/146Nd, a natural tracer: an application to oceanic basalts

1976; Elsevier BV; Volume: 31; Issue: 2 Linguagem: Inglês

10.1016/0012-821x(76)90219-3

1385-013X

Pierre Richard, Nobumichi Shimizu, Claude J. Allègre,

High-pressure geophysics and materials

The possibility of using 143Nd/146Nd as a natural tracer was examined by analyzing two Hercynian granitic rocks, one carbonatite, three alkali basalts and nine tholeiites. 143Nd/146Nd ratios are notably different for these rock types: 0.7068–0.7073 for granitic rocks, 0.7078 for the carbonatite, 0.7080 for alkali basalts and 0.7083 for tholeiites. The isotopic difference between tholeiites and alkali basalts suggests that they are derived from parts of the mantle which have been chemically different. Comparison of the measured 143Nd/146Nd ratio of tholeiites and the isotopic growth in a simple two-stage model system suggests that the source of the tholeiite magmas has had light-REE-depleted pattern, being consistent with Gast's (1968) contention that ridge tholeiites are derived from a part of the mantle which is a residue left after a previous melting event.