A SHORT DESCRIPTION ABOUT THE NIPR, JAPANESE ANTARCTIC METEORITE THIN SECTION COLLECTION

   In 1993, after 20 years of succesful meteorite collecting expeditions on Antarctica, an extraordinary Meteorite Thin Section Educational Set was made - in 20 copies - by the National Institute of Polar Research (NIPR), Tokyo, Japan (Department of Antarctic Meteorites). The Antarctic Meteorite Collection of NIPR made it possible to prepare an almost full set of representative class-types of meteorites, and to give an excellent cross section about the rocky materials of the Solar System asteroidal bodies. This set was completed in 1993 June at NIPR, Department of Antarctic Meteorites, by Keizo Yanai, principal investigator and curator of these Antarctic Meteorites. One copy of this set was given as loan for Hungarian universities, curating by Eötvös University, Cosmic Materials Space Research Group, on the occasion of 19th Symposium on Antarctic Meteorites, held in Tokyo, 31st May - 3rd June, 1993.

1. INTRODUCTION

Meteorites, the material samples from various regions of the Solar System, were collected till the 60-es of our century from random events. These events could be falls and finds, they could contribute both by one and by some thousand meteorite pieces from one event, because events themselves were catalogued. (Till the 70-es about 2500 events.) In the 70-es the ratio of random events to systematically collected meteorites began slowly decrease. Since the last years of 60-es first Japanese, then also American expeditions started to hunt and collect meteorites from the icefields of Antarctica. Meteorite search expeditions became annual events in Japan and United States and after a quarter century of work we may say that this peaceful competition resulted in about 20000 pieces of ANTARCTIC METEORITES. Half of this quantity is stored at the National Institute of Polar Research (NIPR), Tokyo, Japan, and half at the Planetary Materials Laboratory, NASA Johnson Space Center (JSC), Houston, Texas, U.S.A.

2. TRADITIONAL CLASSIFICATIONS OF METEORITES

In the last years of our century (and millennium) since the works of Chladny, Prior, Tschermak, Rose, Howard, Urey, Craig, Mason, Van Schmus, Wood, Wiik, Wasson, Keil, Anders, Ringwood, and Sztrókay, a well known systematics of meteorites have been constructed. This system begins with the distinction of groups of IRONS, STONY-IRONS and STONES, and continues by the distinction within STONES as CHONDRITES and ACHONDRITES, depending on the presence of 0,01 mm - 10 mm spherical or near spherical textural elements in them. New period of classification began with the work of Clayton and Mayeda and other coworkers by oxygene isotopic studies.

The theoretical way of meteorite classification starts from the chemical condensational models of the Solar System. These models were worked out in the last 30 years by a number of authors, of which the most known names are Larimer, Grossman, Lewis, and Barshay. Such models were frequently referred (see i.e. Bérczi & Lukács, 1994) and they can give a sequence of minerals with decreasing crystallizational temperature, as a function of solar distance (and pressure too). This mineral sequence formed mineral belts around the early Sun. With the decreasing solar luminosity these belts moved inward, towards the Sun, so during the crystallization a mixing mechanism also worked. The result can be described in the terms of "main types". (However, in practice, these types also determined by the survival factors during atmospheric entry.) The usual "pure" and "transitional" belt types around the Sun are as follows: IRONS, STONY-IRONS, STONES, ICY-STONES, ICES. Therefore instead of the three types of meteorites in most collections theory predicts five different main types of meteorites. (Bérczi & Lukács 1994). Of course, chances are slight for ices to be preserved in usual terrestrial environments. (This is a remark for future expeditions which may find the missing (since hardly preservable) icy-stone and ice meteorites. And the only chance to find them is on Antarctica. 

Seeing the system of meteorites together in one collection we can recognize that one of the two missing types is almost present: a variety of stony-ices is present in the form of carbonaceous chondrites, because of their abundant volatile content, partly in the form of hydrated silicates. The research of last years revealed aquaeous alteration in many CM CV and CO carbonaceous chondrites which was followed by dehydration (Krot, Scott, Zolensky, 1996, 1997). This sequence of events confirms the role of icy and other water containing components in the formation of the early Solar System materials. 

3. VAN SCHMUS - WOOD TYPE TABLE OF CHONDRITES

In order to give a good background sketch to the studies of chondrites in the NIPR Antarctic Meteorite Thin Section Set we may choose the Van Schmus - Wood classification table for petrographical types of chondrites. There are 18 chondritic thin sections in the set. They can be shown as arranged into the Van Schmus - Wood type table according to their numbers. (See, Bérczi, Holba, Lukács, 1995) This Table can serve as a frame of reference for any such type of chondrite collections, too. Together with the conventional classification tables of chondrites - by their iron plus iron-sulfide versus oxidized iron diagram, well known from Urey, Craig, 1953 - and that of CaO versus FeO/FeO+MgO diagram for achondrites, the Van Schmus - Wood table give the third useful frame of reference for most of the meteorite classification. On these backgrounds now we shortly describe all the 30 thin sections of the Japanese NIPR Antarctic Meteorite Collection.

4. A SHORT DESCRIPTION OF THE THIN SECTIONS IN THE SET

The set contains 30 thin sections, which are as follows. The numbering is according to the set.

N° 1. Pallasite - Yamato 8451.

Large spherulic olivine grains are embedded in the opaque metal phase (nickel-iron).

N° 2. Mesosiderite - Allan Hills 77219.

The sample comprises of large orthopyroxene grains, opaque metal phase and smaller orthopyroxenes and olivines in the groundmass of the texture.

N° 3. Aubrite (Enstatite achondrite) - Allan Hills 78113.

The slightly brecciated texture mainly consists of large enstatite grains. Some regions contain olivine, too.

N° 4. Ureilite - Allan Hills 77257.

The texture consists of large, clear olivine, pyroxene and less plagioclase grains and opaque phase. All the mineral grains have opaque edges, which is very characteristic to the ureilitic texture.

N° 5. Diogenite A - Yamato 74097.

Monomineralic crystalline texture consisting of orthopyroxene.

N° 6. Diogenite B - Allan Hills 77256.

Monomineralic brecciated texture consisting of orthopyroxene.

N° 7. Howardite - Yamato 7308.

Brecciated basaltic achondrite with plagioclase, orthopyroxene and less olivine, and clinopyroxene in the texture.

N° 8. Eucrite A - Yamato 791195.

This basaltic achondritic meteorite has crystalline texture similar to that of a microgabbro with clinopyroxene (also occurs with twin-lamellae) and plagioclase (in subhedral grains).

N° 9. Eucrite B - Yamato 74450.

This basaltic achondrite has brecciated (polymict) texture and consists of plagioclase+pyroxene basaltic clasts, and mineral clasts of these two minerals, too.

N° 10. Shergottite - Allan Hills 77005.

Brown pyroxene and mainly glassy plagioclase (maskelynite) plus some plagioclase minerals and opaque component (chromite?) comprise this basaltic achondritic texture which is suggested to have been originated from Mars. At the edge of one plagioclase grain fine grained plagioclase crystals with glass between them have been formed with variolitic texture. Both diaplectic glass (maskelynite) and this region of melting and recrystallization refers to the impact event which delivered the sample to Earth.

N° 11. Lunar Meteorite A (regolith breccia) - Yamato 86032.

Large plagioclase rich clasts are embedded in a darker matrix. It contain small olivine grains, too. 

N° 12. Lunar Meteorite B (norite) - Asuka 881757 (earlier Asuka 31).

The gabbroic texture of this lunar meteorite sample consists of orthopyroxene and glassy plagioclase (maskelynite). In many respects the sample is very similar to the NASA Lunar Sample N° 78235, which has similar mineral components except that there brown glass veins can also be found in the texture. Considering maskelynite, the Lunar Meteorite B - Asuka 881757 is also similar to the N° 10. Shergottite - Allan Hills 77005 sample, and similarity might have resulted from their excavation from the surface of a planetary body with greater mass than an asteroidal mass.

N° l3. Primitive achondrite - Yamato 794046.

The texture is equigranular and consists of olivines, pale brown pyroxenes embedded into a large, long plagioclase grain. It contains a few opaque minerals (troilite) and brown, almost isotropic glass, interstitially.

N° 14. EH3 chondrite - Yamato 691.

Well developed chondrules mainly consisting of olivine and pyroxene. It contains opaque phases (metal + troilite) too.

N° 15. H3 chondrite - Yamato 791428.

Well developed chondritic texture. The chondrules are both from olivine, plagioclase and pyroxene + opaque component. There are chondrules mixed from these three main mineral phases, too.

N° 16. H4 chondrite - Allan Hills 77233.

The chondrules of this rather weel defined chondritic texture are mainly from clinopyroxenes, and in less number from olivine. 

N° 17. H5 chondrite - Yamato 74079.

Less well developed chondritic texture with chondrules consisting of olivine and pyroxene. (Among meteorites from Hungary Zsadány, Ohaba, and Nagy-Dévény are similar chondrite types.)

N° 18. H6 chondrite - Yamato 74014.

Slightly discernible chondrules. There are chondrules consisting of skeletal olivine. By this chondrule there are also olivine crystals.

N° 19. L3 chondrite - Yamato 74191.

Well developed chondritic texture. It contains mainly chondrules from olivine and pyroxene, and a devitrified brown glass also occurs. (Among meteorites from Hungary: Mezö-Madaras is a similar type chondrite, although with brecciated texture.)

N° 20. L4 chondrite - Yamato 74355.

Chondritic texture with well developed chondrules of olivine and pyroxene.

N° 21. L5 chondrite - Yamato 790957.

Less well defined chondrules, mainly from pyroxenes. (Among meteorites from Hungary: Borkút, Knyahinya and Nagy-Borove are of similar type.)

N° 22. L6 chondrite - Allan Hills 769.

Chondritic texture with poorly defined chondrules. In a large pyroxene grain olivine inclusions can be found, and the pyroxene grain itself is also surrounded by olivine grains. (Among meteorites from Hungary Mócs and Kakova are of this type.)

N° 23. LL3 chondrite - Yamato 790448.

Densely populated with chondrules and chondrule fragments mainly from clinopyroxenes (some are twinned). There is a cellular olivine which contains fine fibre of glass. Lamellar clinopyroxene also occurs with fine devitrifying glass fibres. Between chondrules sulfide type opaque patches occur.

N° 24. LL4 chondrite - Yamato 74442.

A rather well defined chondritic texture with a little bit brecciated character where olivine and pyroxene grains also occur, together with the chondrules.

N° 25. LL5 chondrite - Allan Hills 78109.

Poorly defined chondrules. There are chondrules consisting of barred olivines grown together with lamellae with different directions. Olivine chondrules+opaque minerals+olivine crystals also occur together. (Among meteorites from Hungary Nyírábrány is a similar type.)

N° 26. LL6 chondrite - Yamato 75258.

Poorly defined chondrules, mainly consisting of olivine. There is a chondrule in which olivines radiate from an opaque core. Olivine grains also occur in the fine grained groundmass.

N° 27. CI carbonaceous chondrite - Yamato 82162.

Irregular chondrule-like grains can be found in the dark carbonaceous groundmass. One grain contains fine fibrous material - possibly devitrifying glass.

N° 28. CM2 carbonaceous chondrite - Yamato 74662.

In the dark carbonaceous matrix mainly olivine (clear, transparent) and pyroxene (less clear) chondrules occur.

N° 29. CO3 carbonaceous chondrite - Yamato 791717.

Well developed chondrules embedded into a fine grained groundmass which seems fresh. Spheroidal olivine chondrules occur. In a chondrule olivine, metal phase and haematite occur together. There is a chondrule with skeletal olivine between glass, so forming a spinifex textural character, and this all is surrounded with olivine grains.

N° 30. CV3 carbonaceous chondrite - Yamato 86751.

Well defined chondrules in the fine grained matrix. There is a chondrule with many small olivine and twinned clinopyroxene surrounded with a glassy material. (Among meteorites from Hungary: Kaba is a similar type.)(see Bérczi Sz., Don Gy. et al. 1998)

REFERENCES

Barshay, S.S., Lewis, J.S. 1975: In: The Dusty Universe, eds. Field, G.B., Cameron, A.G.W., Neale Watson Acad. Publ., New York

Bérczi Sz., Don Gy., Gál-Sólymos K., Kubovics I., Lukács B., Martinás K., Nagy B., Puskás Z., Solt P. 1998: Foliated Kaba CV3 chondrite. Antarctic Meteorites XXIII. Abstr. Vol. 

Bérczi Sz. & Lukács B. 1994: KFKI-1994-11, Budapest

Cassidy W., Harvey R., Schutt J., Delisle G., Yanai K.: The meteorite collection sites of Antarctica. Meteoritics, 27. 490-525. 1992.

Krot, A.N., Scott, E.R.D., Zolensky, M. 1996: LPSC XXVII. 711-712.

Krot, A.N., Scott, E.R.D., Zolensky, M. 1997: Meteoritics and Planetary Science, 32. 31-49.

Mittlefehldt D. W. & Lindström M. M. 1994: Antarctic Meteorites XIX. NIPR Symp. Abstr.Vol. 

Tomeoka K., Kojima T. 1995: Antarctic Meteorites XX. NIPR Symp. abstr.vol. 252-254.

Yanai K. & Kojima H.: Photographic Catalog of the Antarctic Meteorites. NIPR. Tokyo, 1987.

Yanai K. & Kojima H.: Varieties of Lunar Meteorites Recovered from Antarctica. Proc. NIPR Symp. Antarct. Meteorites, 4. 70-90. 1991.

Yanai K., Kojima H., Haramura H. 1995: Catalog of Antarctic Meteorites. NIPR, Tokyo

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