IAB meteorites

The IAB meteorite form a group of the basis of their chemical composition iron meteorites . Their various silicate inclusions bring them close to primitive achondrites . There is also a relationship to carbonaceous chondrites and winonaites .

designation

The IAB meteorites, also IAB complex , belong to group I of iron meteorites. They originally formed the two groups IA and IB, but were ultimately amalgamated to IAB because of their chemical similarities (there are transition links).

description

The Goose Lake meteorite , an IAB meteorite of the sLL subgroup

The IAB meteorites are mineralogically composed mainly of meteoric iron (minerals kamacite and taenite ) as well as silicate inclusions. According to the structural classification of iron meteorites, the majority of them belong to the medium to coarse octahedrites with clear Widmanstätten structures (groups Om and Og with Kamacite ridges 0.5 to 3.3 millimeters wide). But hexaedrites and even ataxites also occur within the IAB complex. The silicate inclusions can contain calcium-rich and calcium-poor pyroxenes , olivine and plagioclase . Troilite , graphite , various phosphates , meteoric iron and traces of daubréelite and chromite also act as inclusions .

IAB meteorites are very similar in their composition to the Winonaites and IIICD meteorites already mentioned , but whether they come from the same asteroid is unclear.

Classification

The Nantan meteorite from Guangxi in China

The IAB complex sits next to the IAB main group (IAB-MG) for various sub-groups and small groups ( Engl. Grouplets ) together:

sLL subgroup
sLM subgroup (formerly known as IIIC group)
sLH subgroup (formerly IIID group)
sHL subgroup
sHH subgroup (includes the gay gulch trio)
Udei station group
Pitts group
Algarrabo duo
Oral rabilla duo
Britstown duo
NWA-468 Duo
Twin city duo
unique pieces related to the IAB meteorites

geochemistry

The characteristic limit values exceeded by the IAB complex are:

Nickel > 5.5%
Gold > 1.3 ppm
Arsenic > 10 ppm
Cobalt > 3.9 ppm
Antimony > 0.18 ppm

origin

There are still different opinions about the origin of the IAB meteorites. In general, a non-magmatic mode of origin is assigned to them . Rather, the melts from which they emerged had been generated by impact events, so that melt-crystallizate fractionation effects could only play an insignificant role. Other generation models use an igneous fractionation process , where the heat of fusion is said to have been supplied by radioactive decay of ²⁶ Al. Kelly and Larimer (1977) take the view that the IAB complex is due to the successive enamel secretion of a chondritic parent body.

Significant finds

Etched section of the Canyon Diablo meteorite

Significant finds among the IAB meteorites are:

Individual evidence

^ MK Weisberg, TJ McCoy, AN Krot: Systematics and Evaluation of Meteorite Classification . In: DS Lauretta, HY McSween, Jr. (Eds.): Meteorites and the early solar system II . University of Arizona Press, Tucson 2006, ISBN 978-0-8165-2562-1 , pp. 19-52 .
^ JT Wasson: Meteorites: Classification and Properties . Springer-Verlag, New York 1975.
↑ JT Wasson, GW Kallemeyn: The IAB iron meteorite-complex: A group, five subgroups, Numerous grouplets, closely related, Mainly FORMED by crystal segregation in Rapidly cooling melts . In: Geochimica et Cosmochimica Acta . tape 66 , no. 13 , 2002, p. 2445-2473 , doi : 10.1016 / S0016-7037 (02) 00848-7 .
↑ B. Choi, X. Ouyang, JT Wasson: Classification and origin of IAB and IIICD iron meteorites . In: Geochimica Cosmochimica Acta . tape 59 , 1995, pp. 593-612 .
^ GK Benedix et al .: A petrologic study of the IAB iron meteorites: Constraints on the formation of the IAB Winonaite parent body . In: meteorite. Planet. Sci . tape 35 , 2000, pp. 1127 .
^ KR Kelly, JW Larimer: Chemical fractionation in meteorites - VIII: Iron meteorites and the cosmochemical history of the metal phase . In: Geochimica Cosmochimica Acta . tape 41 , 1977, pp. 93-111 .

[1] MK Weisberg, TJ McCoy, AN Krot: Systematics and Evaluation of Meteorite Classification . In: DS Lauretta, HY McSween, Jr. (Eds.): Meteorites and the early solar system II . University of Arizona Press, Tucson 2006, ISBN 978-0-8165-2562-1 , pp. 19-52 .

[2] JT Wasson: Meteorites: Classification and Properties . Springer-Verlag, New York 1975.

[3] JT Wasson, GW Kallemeyn: The IAB iron meteorite-complex: A group, five subgroups, Numerous grouplets, closely related, Mainly FORMED by crystal segregation in Rapidly cooling melts . In: Geochimica et Cosmochimica Acta . tape 66 , no. 13 , 2002, p. 2445-2473 , doi : 10.1016 / S0016-7037 (02) 00848-7 .

[4] B. Choi, X. Ouyang, JT Wasson: Classification and origin of IAB and IIICD iron meteorites . In: Geochimica Cosmochimica Acta . tape 59 , 1995, pp. 593-612 .

[5] GK Benedix et al .: A petrologic study of the IAB iron meteorites: Constraints on the formation of the IAB Winonaite parent body . In: meteorite. Planet. Sci . tape 35 , 2000, pp. 1127 .

[6] KR Kelly, JW Larimer: Chemical fractionation in meteorites - VIII: Iron meteorites and the cosmochemical history of the metal phase . In: Geochimica Cosmochimica Acta . tape 41 , 1977, pp. 93-111 .