Petrographic and Geochemical Characterization of MIL090206, MIL090405, NWA6077, NWA5363 and NWA11187 Ungrouped Meteorites: New Insights Towards a Potential Classification
2024
Raciti, Mattia Giuseppe
MIL090206, MIL090405, NWA6077, NWA5363 and NWA11187 are achondrite meteorites currently belonging to the ungrouped meteorites. In particular MIL090206, MIL090405, NWA6077, NWA5363 are classified as brachinite-like ungrouped meteorites. NWA11187, resembling an ureilite in the oxygen isotopic values, was then classified as an ungrouped achondrite based on the exsolution lamellae of pigeonite and the forsteritic olivine composition. The aim of this thesis work is to characterize the petrography and the geochemistry of these five samples of meteorites by means of Scanning Electron Microscope (SEM), Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS) and Electron Probe Micro- Analyzer (EPMA) to better constrain their geochemical composition and as a consequence their potential association to a specific achondrite group. All these meteorites have similar mineralogical phases and petrographic textures. They are composed of olivine, orthopyroxene, clinopyroxene, plagioclase and accessory Cl-rich apatite, chromite, troilite and Fe-Ni phases. The samples also display a poikilitic texture. One noticeable difference between NWA11187 and the other four meteorites is the presence of exsolution lamellae of pigeonite in addition to its high magnesium content. NWA11187 displays also important differences in the trace elements chemical data in olivine, orthopyroxene and clinopyroxene. For olivine, NWA11187, has a mean Ca44 value of 1906.36 ppm (other meteorites 544.50-722.21 ppm), for orthopyroxene, has a mean Al27 value of 4612.69 ppm (other meteorites 1228.12-2985.50 ppm), for clinopyroxene, has a mean Mn55 of 2845.29 ppm (other meteorites 1667.42-2024.28 ppm).
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