Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network |
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| Authors: | Kathryn A Dyl Gretchen K Benedix Phil A Bland Jon M Friedrich Pavel Spurný Martin C Towner Mary Claire O'Keefe Kieren Howard Richard Greenwood Robert J Macke Daniel T Britt Angela Halfpenny James O Thostenson Rebecca A Rudolph Mark L Rivers Alex W R Bevan |
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| Institution: | 1. Department of Applied Geology, Curtin University, Perth, WA, Australia;2. CSIRO Earth Sciences and Resource Engineering, Perth, WA, Australia;3. Department of Earth and Planetary Sciences, Western Australian Museum, WA, Australia;4. Department of Chemistry, Fordham University, Bronx, NY, USA;5. Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA;6. Astronomical Institute of the Academy of Sciences, Czech Republic;7. Kingsborough Community College of the City University of New York, Brooklyn, NY, USA;8. Planetary and Space Sciences, The Open University, Milton Keynes, UK;9. Department of Physics, Boston College, Chestnut Hill, MA, USA;10. Vatican Observatory, Vatican City‐State, Italy;11. Department of Physics, University of Central Florida, Orlando, Florida, USA;12. Microscopy and Imaging Facility, American Museum of Natural History, New York, NY, USA;13. Consortium for Advanced Radiation Sources, University of Chicago, Argonne, IL, USA;14. Department of Imaging and Applied Physics, Curtin University, Perth, WA, Australia |
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| Abstract: | Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS‐XRD, element mapping via energy dispersive spectroscopy EDS], and X‐ray tomography for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67?0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α‐quartz and a rim of both low‐ and high‐Ca pyroxene. The mineralogy allows the calculation of the temperatures and ?(O2) characterizing thermal metamorphism on the parent body using both the two‐pyroxene and the olivine‐chromite geo‐oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ?(O2) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism. |
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