Meteorite Collections from Antarctica

Experience has shown that ablation areas that expose bare ice occur in many places on the East Antarctic ice sheet adjacent to the entire length of the Transantarctic Mountains. Many of these areas have yielded a wide variety of meteorite specimens including rocks from the Moon and from Mars listed in Appendices 18.12.3 and 18.12.4. The ongoing search for meteorites by the personnel of ANSMET is one of the most successful programs of the United States Antarctic Program operated by the National Science Foundation. Several summary reports have been published by past and current participants in this enterprise, including especially the book by Cassidy (2003) and reports by Harvey (2003), Cassidy et al. (1992), Cassidy (1991), Cassidy and Harvey (1991), Koeberl (1988a), Marvin and Mason (1980, 1982, 1984), Marvin (1981, 1984, 1989), Marvin and McPherson (1989), Cassidy and Rancitelli (1982), and Cassidy et al. (1977). 

Most of the meteorite specimens that were recovered from the Grove Mountains in East Antarctica weigh less than 10 grams (g) and only 21 specimens weigh more than 100 g. The resulting mass distribution in Fig. 18.6 is fairly typical of meteorite specimens collected on other blue-ice areas on the East Antarctic ice sheet. Evidently, most of the specimens are fragments of meteoroids that exploded in the atmosphere. 

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Figure 4 Ne exposure ages of LL chondrites. Ne ages recalculated with the formulas of Eugster (1988). Multiple analyses for meteorites were averaged. Meteorite finds from Antarctica and northern Africa with similar exposure ages and collected at the same site were treated as paired (source L. Schultz).

The evidence that stony meteorites collected in Antarctica are weathered implies that certain chemical elements are mobilized within the affected meteorite specimens. In addition, glacial meltwater and atmospheric carbon dioxide invade the affected meteorite specimens together with halogens, sulfur-bearing componnds, and organic molecules. Therefore, meteorites that fell on the East Antarctic ice sheet are altered mineralogically as well as chemically and, for that reason, their trace-element concentrations may differ from those of non-Antarctic meteorite falls. 

In subsequent years, the meteorite collectors of ANSMET have found many more lunar meteorites on the icefields adjacent to the Transantarctic Mountains while Japanese investigators recovered ten additional specimens of lunar rocks from the large icefields associated with the Yamato Mountains near the coast of East Antarctica. The lunar meteorites that have been collected in Antarctica are listed in Appendix 18.12.3 (see also Cassidy 2003 Table 7.1). The total mass of the lunar meteorites collected in Antarctica is greater than 2,580 g and continues to increase as additional specimens are recovered. 

Fig. 18.27 The Ar/ Af dates of small particles of impact-melt glass in lunar meteorites collected in Antarctica and in the Saheua Desert of Libya indicate the frequency of explosive impctcts of meteoroids or asteroids on the Moon. The results derived from these samples yield a spectrum of dates ranging from >1.8 to <4.2 billion years. The low abundances of dates older than 3.4 billion years implies that some glass particles older than about 3.4 billion years were destroyed by more recent impacts on the Moon. The Ar/ Ar dates shown here were measured by Cohen et al. (2005)...

The properties of meteorites collected in Antarctica that have been measured include their chemical and mineralogical compositions as well as their textures, isotopic ages, and cosmic-ray exposure histories. The scientific value of the accumulated data is exemplified in this chapter by selected specimens of Antarctic meteorites such as the Derrick Peak iron, by the first lunar meteorite recovered on the icefields of fhe Allan Hills (ALHA 81005), and by the martian rock ALH 84001. The interpretation of data derived from these and other meteorites collected in Antarctica contribute to the on-going exploration of the solar system. 

Eugster O. (1989) History of meteorites from the Moon collected in Antarctica. Science 245, 1197-1202. 

Meteorite specimens that land on the East Antarctic ice sheet are transported to the margins of the ice sheet and may be exposed on the bare-ice fields in the zone of ablation adjacent to the Transantarctic Mountains, and at the Yamato and Grove mountains of East Antarctica. In addition, several dozen rock samples from the Moon and from Mars have been collected in Antarctica. 

The first meteorite discovered in Antarctica was found by a member of Douglas Mawson s expedition from 1911 to 1914 to the Adelie Coast (67°00 S, 139°00 E) of East Antarctica. The meteorite was collected in Commonwealth Bay about 43 km west of Cape Dennison... 

Fig. 18.1 The third meteorite to be collected in Antarctica was a pallasite that was recovered by A.B. Ford on December 7, 1961, in the Thiel Mountains (Ford and Tabor 1971). Pallasites are composed primarily of crystals of olivine with minor low-calcium pyroxene, chromite, and phosphates in a matrix of metaUic iron-nickel alloy. The pallasite in this picture, known as Ahumada, illustrates the composition and texture of the Thiel Mountains pallasite although it was not recovered in Antarctica (Reproduced by permission of A.N. Krot from Krot et al. (2005, Fig. 25b, p. 114) and Elsevier, Inc. through Copyright Qearance Center, Inc. 222 Rosewood Drive, Danvers, MA 01932)...

All of the meteorite specimens collected in Antarctica are listed in the Antarctic Meteorite Newsletters issued twice each year by the Meteorite Working Group at the Johnson Space Center in Houston, Texas. In addition, selected specimens are classified based on petrographic descriptions of thinsections. This information is also published in The Meteoritical Bulletins that are combined with the annual supplements of the journal Meteoritics and Planetary Science. The Meteoritical Bulletins list and describe meteorites recovered from all regions of the Earth including Antarctica. 

Fig. 18.3 Iron meteorites have a chtiracteristic texture which appears on polished and etched surfaces. This texture, called the Widmanstatten pattern, formed during slow cooling and crystallization of liquid iron-nickel in the core of a meteorite parent body. The tear-shaped inclusion is composed of iron sulfide which is immiscible in iron-nickel liquid. The meteorite in this image is Carbo, a IID iron meteorite, which was not collected in Antarctica (Reproduced by permission of H. Haack from Htiack and McCoy (2005, Fig. 8, p. 337) and Elsevier, Inc. through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01932)...

Fig. 18.6 The mass distribution of meteorite fragments recovered by the Chinese Antarctic Research Expedition in 2003 tmd 2006 in the Grove Mounteiins, East Antarctica, is weighted in favor of small specimens weighing less than 10 g which make up 82.3% by number of 951 specimens that were collected. Specimens weighing more than 100 g make up only 2.2% of the collection. The most massive specimen weighed 2,812 g. The high abundance of small meteorite specimens collected in the Grove Mountains is typical of meteorite collections elsewhere in East Antarctica (Data from Weisberg et al. 2009)...

The production of radionuclides in meteoroids that are orbiting the Sun takes place by nuclear spallation and neutron-capture reactions with the atoms of the major elements (Bogard et al. 1995 Leya et al. 2000). The concentration of a particular radionuclide in a stony meteoroid exposed to cosmic rays in Fig. 18.14 initially increases with time until it reaches a state of equilibrium or saturation when its rate of decay is equal to its rate of production. When such a meteoroid enters the atmosphere of the Earth and explodes, the resulting meteorite specimens are assumed to be saturated with respect to the cosmogenic radionuclides they contain. After a meteorite has landed on the surface of the Earth, the production of radionuclides stops because the Earth is protected from cosmic rays by its magnetic field and by the atmosphere. Therefore, the rate of decay of cosmogenic radionuclides decreases with time as each nuclide continues to decay with its characteristic halflife. The terrestrial age of a meteorite specimen collected in Antarctica or anywhere else on the Earth is calculated from the rates of decay of the radionuclides (e.g., C1 or A1) that remain at the time of analysis (Jull 2001). 

Fig. 18.25 Lunar basalt (open circles) collected by the Apollo astronauts and lunar meteorites (solid circles) collected in Antarctica occupy a well-defined area in coordinates of their Fe/ Mn, K/La, and (Fe/Sc) x 0.01 ratios. The achondrites of the HED (Howardite, Eucrite, Diogenite) groups (crosses) lie in a separate field. The SNC (solid triangles) meteorites (Shergottites, Nakhlites, Chassignites) originated from Mars. The sample numbered 1 is ALHA 81005 and 2 is Calkalong which was recovered in the Australian desert. The Fe/Sc ratio was reduced by a factor or 0.01 in order to prevent the data points from crowding into the Fe/Sc corner of the triangle (Data for ALHA 81005 from Korotev et al. 1983 and for the other samples from Hill et al. 1991)...

White P (1989) Downhole logging. In Barrett PJ (ed) Antarctic Cenozoic history from the CIROS-1 Drill Hole, McMurdo Sound. DSIR Bull 245 7-14. Wellington, New Zealand Wight S (1995) Description, chemical composition, and origin of six microscopic spherules collected from the Meteorite Moraine in Antarctica An SEM study. BSc thesis. Department of Geological Sciences, The Ohio State University, Columbus, OH... 

Essentially the same amino acids, and nearly equal quantities of D and L enantiomers, were detected in the Murray meteorite, another type II carbonaceous chondrite [6]. Recent expeditions to Antarctica have returned with a large number of meteorites, many of which are carbonaceous chondrites. These may have been protected from terrestrial contamination by the pristine Antarctic ice. Careful analysis of two of these, the Yamato (74662) and the Allan Hills (77306), both type II carbonaceous chondrites, by ion exchange chromatography, gas chromatography, and GC/MS, have detected a wide variety of both protein and non-protein amino acids in approximately equal D and L abundances [9,10]. Fifteen amino acids were detected in the Yamato meteorite and twenty in the Allan Hills, the most abundant being glycine and alanine. The amino acid content of the Yamato meteorite is comparable with that of the Murchison and Murray, but the Allan Hills contains 1/5 to 1/10 that quantity. Unlike earlier meteorites from other locations, the quantities of amino acids in the exterior and interior portions of the Yamato and Allan Hills meteorites are almost identical [9,10]. Thus, these samples may have been preserved without contamination since their fall in the blue ice of Antarctica, which js 250,000 years old in the region of collection. 

For many years, cosmochemistry depended on the chance discovery of meteorites - either witnessed falls and serendipitous finds, or the dogged determination of a few private collectors who systematically searched for them. That changed in 1969, when Japanese explorers in Antarctica led by Masaru Yoshida stumbled onto meteorites exposed on bare ice. American geologist William Cassidy immediately recognized an opportunity, and with support from the National Science Foundation he mounted a joint expedition with the Japanese to the Allan Hills region of Antarctica in 1977 to recover meteorites. This was the first of many expeditions, sponsored by the National Science Foundation and headed first by Cassidy and later by Ralph Harvey, that have returned to Antarctica every year to collect meteorites (Fig. 1.11). The Japanese have operated a parallel field program in... 

About the same time that meteorites were found in Antarctica, an important collection of meteorites was being put together in Roosevelt County, New Mexico. Over a period from 1966 to 1972, several meteorite hunters collected 140 meteorite specimens representing about 100 separate fall events. This collection demonstrated another way for nature to concentrate meteorites. The meteorites in Roosevelt County were found in blowout areas where up to a meter of soil had been blown away by wind, leaving meteorites in plain view on the hardpan surface. Based on this experience, systematic and successful searches of desert areas in Western Australia have been carried out. Subsequently, the deserts of North Africa have turned out to be especially prolific sources of meteorites. The shifting desert sands expose meteorites that have accumulated over thousands of years. The meteorites are collected by nomads and sold to western collectors. Although most desert meteorites are weathered to some degree, new and rare meteorite classes have been discovered. 

The Apollo astronauts returned 382 kg of lunar sample to Earth, and this collection was supplemented by 326 g of soil samples collected by the Soviet Luna landers. The first lunar meteorite was found in 1982 in Antarctica. Since that time, over 120 lunar meteorites representing about 60 different fall events have been collected. The total mass of these meteorites is -48 kg. About one-third of these meteorites were recovered in Antarctica by American and Japanese teams, and most of the rest were recovered in the deserts of North Africa and Oman. The lunar meteorites have significantly expanded the areas of the Moon from which we have samples. 

The presence of a fusion crust, the color and shape of the surface, the presence of metallic grains, and the unusual densities, in most cases, permit meteorite specimens to be distinguished from terrestrial boulders. These criteria apply to meteorite specimens that occur not only in the cold desert of Antarctica, but also to those that are collected in the hot deserts of the world, and in all other places where meteorites can be found. Even though tens of thousands of meteorite specimens have been collected on the East Antarctic ice sheet, Antarctica is not receiving a higher flux of meteorites compared to other areas of the Earth. The apparent abundance of meteorites is caused primarily by their better preservation in the ice and by the dynamics of the East Antarctic ice sheet. 

M, Kurat G (2001) An estimation of the contemporary micrometeorite flux obttiined from surface snow samples collected in central Antarctica. Abstract Meteorit Planet Sci 36 A52... 

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