On the Application of ²³⁸U, ²³⁵U, and ²³²Th Decay Series Disequilibria to Understanding the Processes and Timescales of Oceanic Basalt Petrogenesis

Understanding how processes of magma genesis and magma differentiation control and modify the chemical composition of erupted lavas from the geochemical measurements of the latter is an under-constrained inverse problem as there is only one known parameter – the measured composition of the erupted lava – but two unknown parameters – the chemical composition and lithology of the source before melting and how melting, crystallization, and melt-rock interactions act to alter the lava en route to the surface. In this invited contribution, we review nearly seven decades of scientific research that demonstrate the potential of U and Th decay series measurements for unraveling the complexities of oceanic magmatism. We review the underlying nuclear theory, geochemical principles, and application of the 238U, 235U, and 232Th decay series for (i) defining the timescales of magma genesis during decompression mantle melting, (ii) establishing the timescales of magma recharge and magma degassing, and (iii) determining the eruption ages of oceanic Quaternary volcanism.