2015 Volume 110 Issue 3 Pages 97-110
This paper presents new Sr–Nd–Pb–Hf isotopic compositions of tholeiitic basalts dredged along the Aden Ridge of the central Gulf of Aden (45.5°E–49°E). Two groups of basalts are identified based on their contrasting spatial distributions and geochemical signatures. Basalts dredged from east of 46.2°E (Group 1) are LREE–depleted but have relatively wide variations in 87Sr/86Sr (0.70278–0.70304) and 206Pb/204Pb (18.21–19.03) and limited 143Nd/144Nd (0.51301–0.51309) and 176Hf/177Hf ranges (0.283224–0.283276; εHf = 15.98–17.83), analogous to the geochemical signature of enriched to depleted normal mid–oceanic ridge basalts (N–MORB). In contrast, the basalts dredged between 45.6°E and 46.2°E (Group 2) are more enriched in incompatible elements [ocean island basalt (OIB)–like] but have little variation in 87Sr/86Sr (0.70323–0.70341), 206Pb/204Pb (19.33–19.49), and 143Nd/144Nd (0.51285–0.51292) and a wide variation in 176Hf/177Hf (0.283020–0.283155; εHf = 8.77–13.54). Isotopic and trace element variations can be attributed to the mixing of three types of mantle source: depleted MORB–type mantle (Component i), matrix mantle of the Afar plume (Component ii), and recycled oceanic crust (Component iii) occurring as blobs, streaks, or ribbons within the plume matrix. Mixing between Components i and ii would have produced Group 1 basalts, and Components ii and iii produced Group 2 basalts. Our data suggest that the Afar plume components were involved in magma genesis westward from 48°E in the Aden Ridge.