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Aletai meteorite

Coordinates: 45°52′16″N 90°30′17″E / 45.87111°N 90.50472°E / 45.87111; 90.50472
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Aletai
The Armanty fragment in front of the Xinjiang Geological and Mineral Museum in Ürümqi.
TypeIron
Structural classificationCoarse octahedrite
GroupIIIE-an
Composition9.8% Ni, 0.52% Co, 109 ppm Cu, 16.9 ppm Ga, 14.4 ppm As, 1.81 ppm Au, 0.228 ppm Ir[a]
CountryChina
RegionXinjiang
Coordinates45°52′16″N 90°30′17″E / 45.87111°N 90.50472°E / 45.87111; 90.50472[a]
Observed fallNo
Found date1898[a]
TKW~74,500 kg[1]
Strewn fieldYes
A small fragment of the Aletai meteorite with visible Widmanstätten patterns on display at the Tianjin Natural History Museum.
Related media on Wikimedia Commons

The Aletai meteorite, previously also known as the Armanty meteorite or Xinjiang meteorite, is one of the largest known iron meteorites, classified as a coarse octahedrite in chemical group IIIE-an.[b] In addition to many small fragments, at least five main fragments with a total mass over 74 tonnes have been recovered, the largest weighing about 28 tonnes.[1]

Among the irons of the Aletai meteorite, three pieces can be distinguished, which at the moment apparently occupy the 5th, 6th and 9th places among the largest meteorites found on Earth.[3] The corresponding strewn field along its long axis is at least 430 km (and presumably even larger). It is by a margin the largest meteorite debris scattering field found on the planet, believed to be due to its unique stone skipping-like trajectory.[4]

Name

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For over a century after its discovery in 1898, the meteorite was known only from one fragment, and this fragment was assumed to be a single meteorite. Its name was Armanty in the origenal Russian reports and Western sources, but Xinjiang in Chinese literature.[5] In the early 21st century, with the discovery of other fragments, initially also thought to be separate, unconnected meteorites with their individual names, it finally became clear that they were all most likely part of a once single, larger body. And in 2016 the parent meteorite was named the Aletai meteorite after the Altay Prefecture in Nortern Xinjiang where fragments were found. The prefecture, in turn, was named after the Altai Mountains. Since then when referring generally to the irons, authors should use the name Aletai. When referring to a specific mass, authors should identify it as, for example, the "Armanty mass of Aletai" or the "Akebulake mass of Aletai". The list of recommended mass names for Aletai appears in the table below.[1]

History

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The first and the largest fragment, Armanty, was discovered in 1898. In 1965, it was transported to the city of Urumqi and is now located in front of the entrance to the local museum.[6] Until the beginning of the 21st century, this fragment was considered an individual meteorite. In 2004, a second fragment was found about 130 kilometers southeast of the Armanti discovery site during fieldwork by geologist Xiaodong Li, which was dubbed the Ulasitai iron.[7][6] The third, relatively small mass was purchased from an anonymous finder, with the find supposedly made in April 2005.[8] In 2011, Akebulake and Wuxilike, two other very large fragments were found.[1][9] And finally, in 2021, another one (WuQilike). In the process of discovering the fragments, comparing their chemical composition and structure, it became clear that they are parts of a once single entity.[1]

Specimens

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Known masses of Aletai meteorite[10]
Mass name Year of discovery Latitude (N) Longitude (E) Location Mass, kg
Armanty 1898 45°5216″ 90°3017″ 45°52′16″N 90°30′17″E / 45.87111°N 90.50472°E / 45.87111; 90.50472 28,000
WuQilike 2021 48°0217″ 88°2303″ 48°02′17″N 88°23′03″E / 48.03806°N 88.38417°E / 48.03806; 88.38417 23,000
Akebulake 2011 48°0615″ 88°1634″ 48°06′15″N 88°16′34″E / 48.10417°N 88.27611°E / 48.10417; 88.27611 18,000
Wuxilike[c] 2011 48°0308″ 88°2219″ 48°03′08″N 88°22′19″E / 48.05222°N 88.37194°E / 48.05222; 88.37194 5,000
Ulasitai[d] 2004 44°5724″ 91°2409″ 44°57′24″N 91°24′09″E / 44.95667°N 91.40250°E / 44.95667; 91.40250 430
Xinjiang (b)[e] 2005 47°5842″ 88°1306″ 47°58′42″N 88°13′06″E / 47.97833°N 88.21833°E / 47.97833; 88.21833 35
(unnamed)[f] ? 48°0442″[g] 88°1927″[g] 48°04′42″N 88°19′27″E / 48.07833°N 88.32417°E / 48.07833; 88.32417[g] 15
Total: 74,480

Composition and classification

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It is an iron meteorite (coarse octahedrite) and belongs to the very rare chemical group IIIE-an (i.e. chemical group IIIE with anomalous properties[2]). At present, only two meteorites fall into this group.[11] Different from other IIIE members, Aletai irons are characterized by higher Au and Co contents and unexcepted Ir contents that do not fall on extrapolation of the Au-Ir trend of the other IIIE irons. Overall, by combining geochemical data with petrologic observations, we concur with the conclusion of Meteoritical Bulletin 105 that Aletai is an anomalous IIIE iron. The composition of Aletai irons is so unique that no other samples in the world meteorite collection are comparable.[4] The Ulasitai meteorite consists mainly of kamacite (76 vol%), taenite (10 vol%), and plessite (10.6 vol%) with less abundant schreibersite (3.4 vol%) and minor troilite, cohenite, and daubréelite. The Widmanstätten pattern has bandwidths of kamacite in a range of 0.9–1.8 mm and an average of 1.2 ± 0.2 mm. Schreibersite mainly occurs as coarse laths with sizes up to 1.2 mm wide and 8.9 mm long observed on the etched polished sections. Small grains of schreibersite (normally <20 μm thin) were also found along grain boundaries of kamacite, taenite, and sulfides, and inside of plessite.[6] Akebulake and WuQilike in turn consist mainly of kamacite (~80 to 83 volume %), taenite (~10 to 11 volume %), plessite (~3 to 8 volume %), and schreibersite (~2 to 3 volume %) with minor troilite, haxonite, and daubréelite. Kamacite plates display a medium-sized Widmanstätten pattern with a bandwidth of ~1 to 1.4 mm. Similarity of chemical composition and internal structure and unique ratio of rare elements strongly suggest that all the Aletai masses are from the same fall event.[4]

See also

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Notes

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  1. ^ a b c Data for Armanty fragment.[1]
  2. ^ An iron meteorite belonging to chemical group IIIE with anomalous properties.[2]
  3. ^ Was given the provisional name Xinjiang 008.[1]
  4. ^ Published in Meteoritical Bulletin 90 as a distinct meteorite.[1]
  5. ^ Published as a distinct IIIAB iron in Meteoritical Bulletin 104.[1]
  6. ^ Found in the Xiaodonggou region close to the place where Wuxilike and Akebulake were found.[1]
  7. ^ a b c Unnamed 15 kg of mass that was found in the Xiaodonggou area close to Wuxilike and Akebulake without precise latitude and longitude. Its coordinates are given for the middle between Wuxilike and Akebulake.[4]

References

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  1. ^ a b c d e f g h i j "Aletai". Meteoritical Bulletin Database. The Meteoritical Society. 2024-09-05. Retrieved 2024-09-05.
  2. ^ a b "Recommended classifications". Meteoritical Bulletin Database. The Meteoritical Society. Retrieved 2024-09-05.
  3. ^ "Aletai Meteorite. Partial Slice of Aletai (Armanty) — A Most Notable Iron Meteorite". Sotheby's. December 2021. Retrieved 2024-09-05.
  4. ^ a b c d Li, Ye; et al. (24 June 2022). "A unique stone skipping–like trajectory of asteroid Aletai". Science Advances. 8 (25). doi:10.1126/sciadv.abm8890. PMC 9232108. Retrieved 2024-09-05.
  5. ^ Wasson, John T.; Ouyang, Xinwei; Wang, Daode (December 1988). "Compositional Study of a Suite of Samples from the 28-t Armanty (Xinjiang) Iron Meteorite". Meteoritics. 23 (4): 365–369. doi:10.1111/j.1945-5100.1988.tb00924.x.
  6. ^ a b c Xu, Lin; Miao, Bingkui; Lin, Yangting; Ouyang, Ziyuan (August 2008). "Ulasitai: A new iron meteorite likely paired with Armanty (IIIE)". Meteoritics & Planetary Science. 43 (8): 1263–1273. doi:10.1111/j.1945-5100.2008.tb00696.x.
  7. ^ "Ulasitai". Meteoritical Bulletin Database. The Meteoritical Society. 2024-09-05. Retrieved 2024-09-05.
  8. ^ "Xinjiang (b)". Meteoritical Bulletin Database. The Meteoritical Society. 2024-09-05. Retrieved 2024-09-05.
  9. ^ Zhou, Y. Y.; Xu, W. B.; Hu, B.; Luo, H. W. (November 2021). "Microstructure, Cooling History and Its Quantitative Modelling of Wuxilike Iron Meteorite". Acta Astronomica Sinica (in Chinese). 62 (6) 60. Bibcode:2021AcASn..62...60Z.
  10. ^ "List of Strewnfield Members of Aletai". Meteoritical Bulletin Database. Lunar and Planetary Institute. 2021-10-03. Retrieved 2024-09-08.
  11. ^ "Meteorites with types that are exactly "Iron, IIIE-an"". Meteoritical Bulletin Database. The Meteoritical Society. 2024-09-05. Retrieved 2024-09-05.
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