INVESTIGATION OF CHONDRULES AND METAL IN ALLENDE (CV3) AND JELICA (LL6) USING X-RAY COMPUTED TOMOGRAPHY

Chondrites are primitive meteorites that contain numerous rounded silicate particles called chondrules. How and when chondrules formed inside chondrites is still uncertain despite numerous studies. In this study, we utilized X-ray Computed Tomography (XRCT) to investigate the shape and size of chondrules and metal phases to constrain formation conditions. Scanning was done at the University of Minnesota’s XRCT lab during a Research Experiences for Undergraduates internship. XRCT has been innovative in the field of geology by providing a nondestructive method for analyzing samples. For meteorite studies this is particularly useful since many of the samples are not available for destructive testing. We chose two meteorites from the collection at the University of Minnesota, Allende and Jelica. Allende is a CV3 carbonaceous chondrite, and Jelica is an LL6 ordinary chondrite. After scanning the samples, we used Avizo Fire to separate the chondrules and metal from the surrounding matrix, allowing us to measure volumes and aspect ratios of the separated particles. In general, chondrules have more spherical shapes than metal grains, and Jelica has fewer but larger chondrules than Allende. Metal grains from Allende are larger and more irregularly-shaped than Jelica’s metal grains, which most likely results from the metal rims encircling chondrules in Allende. Metal grains vary more in shape than in size, and chondrules tend to have a larger range of size variation than shape variation. If the particles within a meteorite had common masses, this would indicate preferential sorting by mass during chondrule formation. The difference in mass between metal grains and chondrules within a single chondrite indicates that there was no sorting by mass within solar nebulae.