Deeply dredged submarine HIMU glasses from the Tuvalu Islands, Polynesia: implications for volatile budgets of recycled oceanic crust

Ocean island basalts (OIB) with extremely radiogenic Pb-isotopic signatures are melts of a mantle component called HIMU (high μ, high U/Pb). Until now, deeply dredged submarine HIMU glasses have not been available, which has inhibited complete geochemical (in particular, volatile element) characterization of the HIMU mantle. We report major, trace and volatile element abundances in a suite of deeply dredged glasses from the Tuvalu Islands. Three Tuvalu glasses with the most extreme HIMU signatures have F/Nd ratios (35.6±3.6) that are higher than the ratio (∼21) for global OIB and MORB, consistent with elevated F/Nd ratios in end-member HIMU Mangaia melt inclusions. The Tuvalu glasses with the most extreme HIMU composition have Cl/K (0.11-0.12), Br/Cl (0.0024), and I/Cl (5-6 × 10) ratios that preclude significant assimilation of seawater-derived Cl. The new HIMU glasses that are least degassed for HO have low HO/Ce ratios (75-84), similar to ratios identified in end-member OIB glasses with EM1 and EM2 signatures, but significantly lower than HO/Ce ratios (119-245) previously measured in melt inclusions from Mangaia. CO-HO equilibrium solubility models suggest that these HIMU glasses (recovered in two different dredges at 2500-3600 m water depth) have eruption pressures of 295-400 bars. We argue that degassing is unlikely to significantly reduce the primary melt HO. Thus, the lower HO/Ce in the HIMU Tuvalu glasses is a mantle signature. We explore oceanic crust recycling as the origin of the low HO/Ce (∼50-80) in the EM1, EM2, and HIMU mantle domains. Key Points: We report geochemical data on the first deeply dredged submarine glasses with a HIMU signature The HIMU glasses have low H2O/Ce The low H2O/Ce is interpreted to relate to mantle recycling of pyroxenit