Implications of high-Mg# adakitic magmatism at Hunter Ridge for arc magmatism of the Fiji - Vanuatu region

• Record of adakitic high-Mg# magmatism along Hunter Ridge and Kadavu Island. records limited contribution from subducted sediments. Sr-Nd-Pb arc rocks record the melting subducting South Fiji MORB crust. This slab-melt component is also recorded in common (non-adakitic) rocks. Dehydration serpentinites leads to flux-melting unaltered MORB. The mostly submarine Ridge, located SW Pacific a ∼12 Myr present history related opening North Basin subduction oceanic lithosphere Basin. Although probably composed primarily an older Vitiaz-related basement, young volcanic features are Matthew Island Some dredged these have low-FeO affinities, ranging picrites andesites dacites. Elevated Sr (500 – 3400 ppm) Sr/Y (50 240) coupled fractionated (adakitic) rare-earth element patterns (La/Yb = 5 40, Gd/Yb 1.5 5.7) indicate garnet-signature derived eclogite-facies basalt. Pacific-type Nd-Hf-Pb isotopic ratios contrast with Indian-type nature underlying mantle but match closely ocean Low values Th/La (< 0.15), Ba/La 22), unradiogenic 87 Sr/ 86 (0.7026 0.7032) Pacific-MORB that sediment minor contributor source. data clearly connect all compositions (picrites, low- medium K 2 O lavas, basalts, dacites) source components predominantly within plate. Unradiogenic 0.7029) at high abundances (700 1400 hot-slab localities interpreted reflect under conditions driven by dehydration Such can be detected more Vanuatu as well. Evidence slab western indicates likely occurrence convergent margins.