Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network

Journal Article · Wed Feb 17 00:00:00 EST 2016 · Meteoritics and Planetary Science

DOI:https://doi.org/10.1111/maps.12605· OSTI ID:1401190

Dyl, Kathryn A. ^[1]; Benedix, Gretchen K. ^[2]; Bland, Phil A. ^[2]; Friedrich, Jon M. ^[3]; Spurný, Pavel ^[4]; Towner, Martin C. ^[5]; O'Keefe, Mary Claire ^[6]; Howard, Kieren ^[7]; Greenwood, Richard ^[8]; Macke, Robert J. ^[9]; Britt, Daniel T. ^[10]; Halfpenny, Angela ^[11]; Thostenson, James O. ^[12]; Rudolph, Rebecca A. ^[12]; Rivers, Mark L. ^[13]; Bevan, Alex W. R. ^[14]

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1. Department of Applied Geology Curtin University GPO Box U1987 Perth WA 6845 Australia, CSIRO Earth Sciences and Resource Engineering 26 Dick Perry Avenue Kensington Perth WA 6151 Australia
2. Department of Applied Geology Curtin University GPO Box U1987 Perth WA 6845 Australia, Department of Earth and Planetary Sciences Western Australian Museum Locked Bag 49 Welshpool DC WA 6986 Australia
3. Department of Chemistry Fordham University Bronx NY 10458 USA, Department of Earth and Planetary Sciences American Museum of Natural History New York NY 10024 USA
4. Astronomical Institute of the Academy of Sciences Fričova 298 CZ‐251 65 Ondřejov Observatory Czech Republic
5. Department of Applied Geology Curtin University GPO Box U1987 Perth WA 6845 Australia
6. Department of Chemistry Fordham University Bronx NY 10458 USA
7. Department of Earth and Planetary Sciences American Museum of Natural History New York NY 10024 USA, Kingsborough Community College of the City University of New York 2001 Oriental Boulevard Brooklyn NY 11235 USA
8. Planetary and Space Sciences The Open University Walton Hall Milton Keynes MK7 6AA UK
9. Department of Physics Boston College Chestnut Hill MA 02467 USA, Vatican Observatory V‐00120 Vatican City‐State Italy
10. Department of Physics University of Central Florida Orlando Florida USA
11. CSIRO Earth Sciences and Resource Engineering 26 Dick Perry Avenue Kensington Perth WA 6151 Australia
12. Microscopy and Imaging Facility American Museum of Natural History New York NY 10024 USA
13. Consortium for Advanced Radiation Sources University of Chicago Argonne IL 60439 USA
14. Department of Earth and Planetary Sciences Western Australian Museum Locked Bag 49 Welshpool DC WA 6986 Australia, Department of Imaging and Applied Physics Curtin University Kent Street Bentley Perth WA 6102 Australia

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 ƒ(O ₂ ) 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 ƒ(O ₂ ) 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 OC s and likely exogenous; however, the green object itself may result from metamorphism.

• Sponsoring Organization: USDOE
• Grant/Contract Number: DE‐FG02‐94ER14466; DE‐AC02‐06CH11357
• OSTI ID: 1401190
• Journal Information: Meteoritics and Planetary Science, Journal Name: Meteoritics and Planetary Science Vol. 51 Journal Issue: 3; ISSN 1086-9379
• Publisher: Wiley-Blackwell
• Country of Publication: United States
• Language: English