Helium Isotope Variations in Gulf of Aden Basalts and the Surface Expression of Mantle Heterogeneity During Afar Plume—Triple Junction Interaction

New helium isotope data for basalt glasses from the Gulf of Tadjoura and Gulf of Aden reveal a mantle plume signal that has 3 He/ 4 He up to 17 R A . In the Gulf of Aden, plume helium is detectable ∼380 km from the Afar triple junction, up to the Shukra El Sheik Fracture Zone along the West Sheba Ridge, but not beyond. The trace of the fracture zone onto the coastal margins also marks the eastward extent of volcanic terranes attributed to Afar plume influence on the ocean‐continent transition. The lack of elevated 3 He/ 4 He beyond this point and the history of westward propagation of spreading in the Gulf of Aden toward the triple junction indicate that the Afar plume has a limited influence on modern‐day crustal accretion along most of the Sheba Ridge. Eastward of the Afar plume influence, basalts show uniform 3 He/ 4 He = 8.08 ± 0.20 R A (1 σ , n = 22) along >1,100 km of the ridge axis. This is among the most uniform sections of the global mid‐ocean ridge system for helium isotopes. The uniformity likely results from enhanced homogenization by small‐scale convection in the upper mantle beneath ultra‐slow spreading ridges. Regional He–Pb–Nd–Sr isotope variations follow a pattern similar to that for ocean island basalts, showing a decrease in 3 He/ 4 He as the proportion of recycled material increases in the mantle source region. Source contributions include the Afar mantle plume, shallow asthenosphere, Pan‐African lithosphere, and a sporadic HIMU component that originates either from the continental lithosphere or from within the Afar plume.