The low Re abundance in arc-type volcanic rocks characterized by high 187Os/188Os ratios is an unsolved puzzle of the 187Re-187Os isotope system, leaving a significant gap in our understanding of the evolution of the upper mantle–continental crust system. Here we report new observations of high Re concentrations in fresh, submarine-erupted—i.e., relatively undegassed—island arc–like volcanic glasses dredged from the eastern Manus Basin, offshore Papua New Guinea. These observations, together with previously published reports of high Re concentrations in arc-type melt inclusions, indicate that undegassed arc-type volcanic rocks and the mantle wedge are enriched in Re. Consequently, the Re concentration in the continental crust is likely to be as high as ∼2 ppb, much higher than previously estimated. The low Re concentrations in subaerial arc-type volcanic rocks are probably due to Re loss during magma degassing.

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