gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.1.175 Coupling of Radiogenic Isotopes and ²³⁸U-²³⁰Th-²²⁶Ra Radioactive Disequilibria in Historical Volcanics from the Azores Claude-Ivanaj C. Max-Plank-Institüt für Chemie, Abteilung Geochemie, Postfach 3060, D-55020 Mainz, Germany Allègre C. J. Laboratoire de Géochimie et Cosmochimie, Institut de Physique du Globe de Paris, 4, P1. Jussieu, 75052 Paris cedex 05, France 1998 62A 1 333 334 Copyright © 1998, The Mineralogical Society 1998