Chapter 7: Studies of short-lived radionuclides in Santorini volcanics

Disequilibria between the short-lived radioactive nuclides ²²⁶Ra, ²³⁰Th and ²³⁸U in young volcanic rocks can be used both for dating the time of crystallisation of a rock, and as isotopic tracers of the sources of magmas and the chemical evolution of volcanic systems. The principles of these methods have been reviewed extensively elsewhere (Condomines et al. 1988; Gill et al. 1992; Gill & Condomines 1992; Macdougall 1995). In this chapter, we present new ²³⁸U-²³⁰Th-²²⁶Ra disequilibria data for the Thera pyroclastics and for selected lavas. These data complement the radiogenic isotopic data presented in Chapter 6 on the compositional evolution through time of the pyroclastic ejecta. In particular, we find that the (²³⁰Th/²³²Th) isotopic ratio corrected to the time of eruption varies in a systematic way with time through the second cycle of the Thera pyroclastics and variations in this ratio are correlated with the variations of ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd and Pb isotopes.