Sr-Nd-Pb-Hf isotopic constraints on the diversity of magma sources beneath the Aden Ridge (central Gulf of Aden) and plume-ridge interaction

Abstract

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 87 Sr/ 86 Sr (0.70278-0.70304) and 206 Pb/ 204 Pb (18.21-19.03) and limited 143 Nd/ 144 Nd (0.51301-0.51309) and 176 Hf/ 177 Hf 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 87 Sr/ 86 Sr (0.70323-0.70341), 206 Pb/ 204 Pb (19.33-19.49), and 143 Nd/ 144 Nd (0.51285-0.51292) and a wide variation in 176 Hf/ 177 Hf (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.