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Graves Nunataks (GRA) 06128 and 06129 (ungrouped achondrite)

Antarctica

description from
Antarctic Meteorite Newsletter, Vol. 60, No. 2, August, 2007

Sample No.: GRA 06128; GRA 06129
Location: Graves Nunataks
Field No.: 17918; 17713
Dimensions (cm): 8.5 x 4.0 x 7.5; 8.0 x 5.0 x 2.5
Weight (g): 447.6; 196.450
Meteorite Type: Achondrite Ungrouped

Macroscopic Description: Kathleen McBride

50% of the exteriors has shiny to glassy patches of black fusion crust. The exposed interior is rusty yellow in color and has fractures in a sort of plate-like orientation. The interior has small areas of gray crystalline material. It is a rusty to yellow-ocher color and very weathered.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach, Glenn MacPherson and Lauren LaCroix

The sections exhibit a granoblastic texture dominated by sodic plagioclase (>70 vol. % in the section studied) with lesser olivine and two pyroxenes, although mafic-rich pockets reaching several mm in size are present. Grain size is very heterogeneous; in one large feldspathic region the crystals are up to 5 mm, but elsewhere are rarely as large as 1 mm, perhaps suggesting formation as a breccia. Minor opaques include ilmenite (1.6% MgO), troilite, Fe,Ni-sulfide (pentlandite; 26% Ni), spinel (13% TiO2, 35% Cr2O3, 3% Al2O3), and Ni-Fe metal (67% Ni) that occurs only as minute inclusions inside of olivine. Silicates are equilibrated with olivine of Fa59, orthopyroxene of Fs44Wo2 (Fe/Mn ≈ 43), clinopyroxene of Fs19Wo43 (Fe/Mn ≈ 30-45) and oligoclase (An14Or2). The combination of its variable grain size, locally granoblastic texture, iron-rich mafics and sodium-rich plagioclase is unlike any known achondrite, including those of planetary origin.

Oxygen isotopic analysis: Z. Sharp, University of New Mexico

Oxygen isotopic analyses of three small (2-5 mg) pieces of GRA 06129 yielded the following results which fall in the Earth, Moon and enstatite meteorite field:

δ17O = 3.04, δ18O = 6.01, Δ18O = -0.09
δ17O = 2.89, δ18O = 5.63, Δ18O = -0.03
δ17O = 3.05, δ18O = 6.01, Δ18O = -0.07

[where Δ18O = δ17O - 0.52 x δ18O]

 

 

GRA 06128 in the field.
Mass of stone: 447.6 g

Photo stolen from Antarctic Meteorite Location and Mapping Project.

 

GRA 06129 in the field.
Mass of stone: 196.5 g

Photo stolen from Antarctic Meteorite Location and Mapping Project.
 


Below: Click on image for enlargement. All photos to same scale.
All photos by Randy Korotev.

Four views of a 334-mg chip of GRA 06128.
   
Four views of a 406-mg chip of GRA 06128.
   
Two views of a 334-mg chip of GRA 06129.
   
Two views of a 372-mg chip of GRA 06129.
   
Two views of a broken 318-mg chip of GRA 06129.



Technical Literature

Arai T., Tomiyama T., Saiki K., and Takeda H. (2008) Unique achondrites GRA 06128/06129: Andesitic partial melt from a volatile-rich parent body (abstract). In Lunar and Planetary Science XXXIX, abstract no. 2465, 39th Lunar and Planetary Science Conference, Houston.

Ash R. D., Day J. M. D., McDonough W. F., Bellucci J., Rumble D. III, Liu Y., and Taylor L. A. (2008) Petrogenesis of the differentiated achondrite GRA 06129: Trace elements and chronology (abstract). In Lunar and Planetary Science XXXIX, abstract no. 2271, 39th Lunar and Planetary Science Conference, Houston.

Liu Y., Taylor L. A., Richard R. D., and Day J. M. D. (2008) Mineralogy and petrography of a Sstrange achondrite GRA 06129 (abstract). In Lunar and Planetary Science XXXIX, abstract no. 1830, 39th Lunar and Planetary Science Conference, Houston.

Mikouchi T. and Miyamoto M. (2008) Mineralogy and pyroxene cooling rate of unique achondritic meteorite GRA 06129 (abstract). In Lunar and Planetary Science XXXIX, abstract no. 2297, 39th Lunar and Planetary Science Conference, Houston.

Rumble D. III, Irving A. J., Bunch T. E., Wittke H. J., and Kuehner S. M. (2008) Oxygen isotopic and petrological diversity among brachinites NWA 4872, NWA 4874, NWA 4882 and NWA 4969: How many ancient parent bodies? (abstract). In Lunar and Planetary Science XXXIX, abstract no. 1974, 39th Lunar and Planetary Science Conference, Houston.

Shearer C. K., Papike J. J., Burger P. V., Karner J. M., Borg L. E., Gaffney A. M., Neal C. R., Shafer J., Fernandes V. A., Sharp Z., Weiss B. P., and Geissman J. (2008) GRA 06129: A meteorite from a new asteroidal geochemical reservoir or Venus? (abstract). In Lunar and Planetary Science XXXIX, abstract no. 1825, 39th Lunar and Planetary Science Conference, Houston.

Treiman A. H., Morris R. V., Kring D. A., Mittlefehldt D. W., and Jones J. H. (2008) Petrography and origin of the unique achondrite GRA 06128 and 06129: Preliminary results (abstract). In Lunar and Planetary Science XXXIX, abstract no. 2215, 39th Lunar and Planetary Science Conference, Houston.

Zeigler R. A., Jolliff B. L., Korotev R. L., Rumble D. III, Carpenter P., and Wang A. (2008) Petrology, geochemistry, and likely provenance of unique achondrite Graves Nunataks 06128 (abstract). In Lunar and Planetary Science XXXIX, abstract no. 2456, 39th Lunar and Planetary Science Conference, Houston.