High-precision in-situ Sr isotope analyses in apatite inclusions in zircon: A new proxy for constraining secular changes in the composition of the continental crust

The composition and tectonic setting of formation of the crust during the earliest stages of Earth’s evolution remains debated, and Archaean rocks and minerals preserved in cratonic environments constitute the primary means for investigating early crust. Recent advancements in analytical techniques have propelled the investigation of strontium (Sr) isotopes in apatite, particularly when included in zircon, facilitating insights into the primary signatures of magmatic sources. This presentation introduces a novel approach employing LA-MC-ICP-MS to achieve unprecedented spatial resolution, internal precision and external reproducibility, showing a significant improvement over conventional technique. When applied to Palaeozoic and Archaean granitoids, the newly developed analytical technique allowed to demonstrate the ability of apatite inclusion in zircon to record the original Sr geochemical composition of their magmatic source and investigate the degree of differentiation of juvenile magmas.