Crystallographically controlled alignment of melt inclusion entrapment in magmatic olivine: Insights from Lab-Diffraction Contrast Tomography

Laboratory Diffraction Contrast Tomography (LabDCT) is a recent analytical development that allows for non-destructive microstructural characterisation of crystalline materials using a laboratory-scale X-ray microscope. In this study, we apply LabDCT to investigate magmatic olivine crystals hosting melt inclusion populations with preferential alignment. Melt inclusions provide valuable insights into magmatic and volcanic processes, and are often the subject of extensive geochemical investigation. Destructive sample preparation can prematurely erase contextural information such as inclusion geometries, population characteristics, and the relationship between the inclusion and its host crystal. The approach used in this study shows a clear crystallographic control on melt inclusion orientations where a visual alignment is identified. Melt inclusions consistently align parallel with the a-axis ([100]) of their olivine hosts. This alignment suggests that inclusion entrapment occurred during rapid, skeletal olivine growth, likely the result of thermal disequilibrium and undercooling within the magmatic system. This insight was gained without destructive sample preparation, highlighting the value of these X-ray imaging techniques for microstructural investigation and sample characterisation. This study demonstrates the range of opportunities available by applying non-destructive, three-dimensional X-ray imaging techniques to investigate geomaterials. The method described and applied in this study can be used to compare the orientation of any internal feature to its mineral host, such as melt inclusions and their host olivine crystals.