Déséquilibres radioactifs 238U-230Th-226Ra, 235U-231Pa et phénomènes magmatiques

This paper presents the main results obtained with the 238 U- 230 Th- 226 Ra, 235 U- 231 Pa disequilibria studied in volcanic rocks. In addition to their interest for dating recent volcanic rocks or for studying magmatic sources (through the 230 Th 232 Th isotope ratios), radioactive disequilibria provide unique information on both the processes and the time scales of melting and magmatic differentiation. These studies were initially concentrated on 238 U- 230 Th disequilibria and have been now extended to shorter lived isotopes like 226 Ra or 231 Pa.