Melting dynamics beneath the tonga-kermadec island arc inferred from (231)Pa-(235)U systematics

Measurement of (231)Pa-(235)U disequilibrium in Tonga-Kermadec island arc lavas (north of New Zealand) permits discrimination of the time scales and mechanisms of fluid addition and partial melting. For Tonga lavas, the ((231)Pa/(235)U) ratios are less than 1 and can be explained by fluid addition from the subducting plate around 60,000 years ago. In contrast, the effects of partial melting overprinted those of fluid addition in the Kermadec lavas resulting in ((231)Pa/(235)U) ratios greater than 1.