Melting Dynamics Beneath the Tonga-Kermadec Island Arc Inferred from 231Pa-235U Systematics
Bernard Bourdon,
1*
Simon Turner,
2
Claude Allègre
1
Measurement of 231Pa-235U 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
(231Pa/235U) 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
(231Pa/235U) ratios greater than 1.
1 Laboratoire de Géochimie et
Cosmochimie, Institut de Physique du Globe de Paris-CNRS, UMR7579, 4 Place Jussieu, 75252 Paris Cedex 05, France.
2 Department of Earth Sciences, The Open University,
Milton Keynes MK7 6AA, UK.
*
To whom correspondence should be addressed. E-mail:
bourdon{at}ipgp.jussieu.fr
