Improving magmatic CO₂ reconstruction using X-ray Computed Tomography to accurately quantify melt inclusion volumes and geometries

Melt inclusions provide a critical archive of primary magmatic compositions, particularly for reconstructing volatile systematics that are otherwise obscured by syn-eruptive degassing. Accurate quantification of volatile species such as CO₂ requires robust determination of both melt and vapour bubble volumes within polyphase inclusions. Conventional 2D optical measurements impose simplified geometries and assumptions, introducing significant and often unquantifiable errors. Here we demonstrate that X ray Computed Tomography (XCT), a non destructive, high resolution 3D imaging technique, provides substantially more accurate and reproducible melt inclusion and bubble volume measurements across a large dataset of olivine hosted inclusions. Comparison with traditional methods reveals that 2D approaches can overestimate bubble volumes by 14–40%, with errors expected to rise substantially in inclusions with complex morphology. XCT not only improves volumetric accuracy but also enables explicit uncertainty evaluation through repeat scanning and variable image processing. These advancements significantly enhance CO₂ reconstructions and thereby refine estimates of magmatic volatile budgets, storage depths, and magmatic compositions.