Winonaite

Winonaites
— Group —
Type Primitive achondrite
Subgroups
  • None
Parent body Winonaite-IAB-IIICD[1]
Total known specimens 25

Winonaites are a group of primitive achondrite meteorites. Like all primitive achondrites, winonaites share similarities with chondrites and achondrites.[1][2] They show signs of metamorphism, partial melting, brecciation and relic chondrules. Their chemical and mineralogical composition lies between H and E chondrites.[1]

Naming and history

The winonaite group is named after the type specimen, the Winona meteorite. The name itself derived from Winona, Arizona where the type specimen was said to be found during an archaeological excavation of the Sinagua village Elden Pueblo in September 1928. The Sinagua lived in the village between 1150 and 1275. The meteorite was said to be retrieved from the cist of one of the rooms.[3][4] However, a later study indicates the meteorite was found at another Sinagua site and not in Elden Pueblo.[5] Currently 25 meteorites are included in the winonaite group.[6]

Description

Winonaites are achondrites that have a chemical and mineral composition similar to chondrites. Their composition lies between H and E chondrites.[1] Their isotopic ratios are similar to the silicate inclusions in IAB meteorites. In thin section, the mineral grains show microstructures of extensive thermal metamorphism and signs of partial melting.[7] Some winonaite specimen appear to have relics of chondrules (e.g. Pontlyfni and Mount Morris).[8]

Parent body

Winonaites and the two iron meteorite groups IAB and IIICD are thought to be derived from the same parent body. The iron meteorites formed part of the core of the planetesimal and the winonaites were closer to the surface. The reasoning is that the silicate inclusions in IAB meteorites are similar to winonaites, especially in their oxygen isotope ratios. It is less clear whether IIICD meteorites are also part this parent body.[1][7] The winonaites show that the parent body was affected by impacts that formed breccias of different lithologies. Later these breccias were heated and Ar-Ar radiometric ages have constrained the metamorphism on the parent body to between 4.40 and 4.54 billion years. The parent body also reached temperatures where partial melting took place. Cosmic ray exposure ages show that the meteorites took about 20 to 80 million years to reach earth.[8]

Notable winonaite meteorites

See also

References

  1. 1 2 3 4 5 M. K. Weisberg; T. J. McCoy; A. N. Krot (2006). "Systematics and Evaluation of Meteorite Classification". In D.S. Lauretta; H.Y. McSween, Jr. Meteorites and the early solar system II (PDF). foreword by Richard P. Binzel. Tucson: University of Arizona Press. pp. 19–52. ISBN 978-0816525621. Retrieved 14 October 2013.
  2. ↑ "PAC Group - Primitive Achondrites". Meteorite.fr. Retrieved 10 December 2012.
  3. ↑ "Winona". meteorites.com.au. Retrieved 5 December 2012.
  4. ↑ M. M. Grady Catalogue of Meteorites (5th ed.) Cambridge UP, 2000, p. 528
  5. ↑ A. L. Christenson "J. W. Simmons' account of the discovery of the Winona meteorite."Meteorite 10(3):14-16, 2004
  6. ↑ "Meteoritical Bulletin Database". Meteoritical Society.
  7. 1 2 3 4 Floss, Christine; CROZAZ, Ghislaine; JOLLIFF, Brad; BENEDIX, Gretchen; COLTON, Shannon (1 April 2008). "Evolution of the winonaite parent body: Clues from silicate mineral trace element distributions". Meteoritics & Planetary Science. 43 (4): 657–674. doi:10.1111/j.1945-5100.2008.tb00676.x.
  8. 1 2 Benedix, G.K.; McCoy, T.J.; Keil, K.; Bogard, D.D.; Garrison, D.H. (30 June 1998). "A petrologic and isotopic study of winonaites: evidence for early partial melting, brecciation, and metamorphism". Geochimica et Cosmochimica Acta. 62 (14): 2535–2553. doi:10.1016/S0016-7037(98)00166-5. Retrieved 14 October 2013.
  9. ↑ Floss, Christine; Bradley L. Jolliff; Gretchen K. Benedix; Frank J. Stadermann; Jay Reid (2007). "Hammadah al Hamra 193: The first amphibole-bearing winonaite". American Mineralogist. 92 (4): 460–467. doi:10.2138/am.2007.2253. Retrieved 6 December 2012.
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