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Displaying 21 - 30 from the 33 total records
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Schreibersite Growth and Its Influence on the Metallography of Coarse-Structured Iron Meteorites
Roy S. Clarke, Jr. and Joseph I. Goldstein
80 pages, 28 figures, 20 tables
1978 (Date of Issue: 14 April 1978)
Number 21, Smithsonian Contributions to the Earth Sciences
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Abstract

The role that schreibersite growth played in the structural development process in coarse-structured iron meteorites has been examined. The availability of many large meteorite surfaces and an extensive collection of metallographic sections made it possible to undertake a comprehensive survey of schreibersite petrography. This study was the basis for the selection of samples for detailed electron microprobe analysis. Samples containing representative structures from eight chemical Groups I and IIAB meteorites were selected.

Electron microprobe traverses were made across structures representative of the observed range of schreibersite associations. Particular emphasis was placed on schreibersite-kamacite interface compositions. An analysis of these data has led to a comprehensive description of the structural development process.

Massive schreibersite, one of the four major types of schreibersite encountered, may be accounted for by equilibrium considerations. Subsolidus nucleation and growth with slow cooling from temperatures at least as high as 850° C, and probably much higher, explain the phase relationships that one sees in meteorite specimens. The retention of taenite in the octahedrites establishes that bulk equilibrium did not extend as low as 550° C. Schreibersite undoubtedly continued in equilibrium with its enclosing kamacite to lower temperatures.

A second type of schreibersite to form is homogeneously nucleated rhabdite. It nucleated in kamacite in the 600° C temperature range, either as a consequence of low initial P level or after local P supersaturation developed following massive schreibersite growth.

A third type of schreibersite is grain boundary and taenite border schreibersite. It formed at kamacite-taenite interfaces, absorbing residual taenite. Nucleation took place successively along grain boundaries over a range of temperatures starting as high as 500° C or perhaps slightly higher. Grain boundary diffusion probably became an increasingly important factor in the growth of these schreibersites with decreasing temperature.

The fourth type of schreibersite is microrhabdite. These schreibersites nucleated homogeneously in supersatuated kamacite at temperatures in the 400° C range or below.

P diffusion controlled the growth rate of schreibersite. The Ni flux to a growing interface had to produce a growth rate equal to that established by the P flux. This was accomplished by tie line shifts that permitted a broad range of Ni growth rates, and these shifts account for the observed range of Ni concentrations in schreibersite. Equilibrium conditions pertained at growth interfaces to temperatures far below those available experimentally. Kinetic factors, however, restricted mass transfer to increasingly small volumes of material with decreasing temperature.


Mineral Sciences Investigations 1976-1977
Robert F. Fudali, editor
73 pages, 22 figures, 20 tables
1979 (Date of Issue: 11 September 1979)
Number 22, Smithsonian Contributions to the Earth Sciences
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Abstract

This volume is comprised of six short contributions reporting the results of some of the research carried out by the Department of Mineral Sciences, Smithsonian Institution, during the period 1976-1977. Included are: a comparison of impact breccias and glasses from Lonar Crater (India) with very similar specimens from the moon; petrographic descriptions and chemical analyses of virtually all the known pyroxene-plagioclase achondrite meteorites and a discussion of the relationships within this class; a comparative chemical study of sixty Australian tektites from widely separated localities; a description of a new, rapid technique of sample preparation for whole-rock analyses using the electron microprobe; an interlaboratory comparison of the precision and accuracy of electron microprobe analyses; and a tabulation of the chemical compositions of some electron microprobe reference samples.


Catalog of Antarctic Meteorites, 1977-1978
Ursula B. Marvin and Brian Mason, editors
50 pages, 39 figures, 2 tables
1980 (Date of Issue: 25 July 1980)
Number 23, Smithsonian Contributions to the Earth Sciences
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Abstract

During two expeditions to Antarctica (1976-77 and 1977-78), more than 300 pieces of meteorites were collected from a small area adjacent to the Allan Hills (77°S, 159°E) in Victoria Land. The 1977-78 meteorites were collected with special care to avoid contamination, and were transported in frozen condition to the Johnson Space Center, Houston, where they were processed under similar conditions to those used for the lunar samples. Eighty-five specimens of the 1977-78 collection, including most of those weighing over 100 grams, have been characterized, and are described in this monograph. Appendices provide a listing of these in numerical sequence and with significant data, and a table of chemical analyses. A summary of the published data on the ten meteorites of the 1976-77 collection is also included.


Catalog of Meteorites from Victoria Land, Antarctica, 1978-1980
Ursula B. Marvin and Brian Mason, editors
97 pages, 41 figures, 13 tables
1982 (Date of Issue: 29 July 1982)
Number 24, Smithsonian Contributions to the Earth Sciences
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Abstract

This is the second catalog of meteorite specimens collected on expeditions to Victoria Land led by William A. Cassidy of the University of Pittsburgh. The first (Catalog of Antarctic Meteorites, 1977-1978, U. B. Marvin and B. Mason, editors, 1980) presented the results of the 1976-1977 and 1977-1978 field seasons and described the collection and curation procedures that were adopted under a three-agency agreement between the National Science Foundation, the National Aeronautics and Space Administration, and the Smithsonian Institution for the purpose of protecting the meteorites from terrestrial contamination and allocating them for research. This catalog reports the results of the subsequent two seasons: 309 specimens were collected in 1978-1979, and 73 in 1979-1980. Classifications are given for all specimens weighing more than about 100 grams and also for some smaller pieces from each of the four field seasons. The catalog describes the field camps, the geodetic measurements of ice motion and ablation at the Allan Hills site, and the search for new concentrations. Current information about the character of the collections and new types of meteorites represented in them is outlined in brief articles describing Antarctic achondrites, carbonaceous chondrites and irons, and meteorite weathering and terrestrial residence times on the polar icecap. There is a bibliography of major articles on Antarctic meteorites. An Appendix lists all of the Victoria Land specimens classified as of December 1980, by numerical order for each locality and by meteorite class.


Inclusions in the Allende Meteorite
Brian Mason and S. R. Taylor
30 pages, 25 figures, 5 tables
1982 (Date of Issue: 5 October 1982)
Number 25, Smithsonian Contributions to the Earth Sciences
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Abstract

Six discrete groups of inclusions have been distinguished in the Allende meteorite. Groups I, V, and VI are mostly melilite-rich chondrules, although some have been extensively altered to fine-grained aggregates; Groups II and III are mostly fine-grained aggregates made up largely of spinel and fassaite; Group IV are olivine-rich aggregates and chondrules. Each group has a distinctive trace-element pattern, most clearly shown by the rare-earth (RE) distribution pattern. Group I has an unfractionated pattern (except for a small positive Eu anomaly) at about 10-15 times chondrites; Group II has a highly fractionated pattern with depletion of the heavier lanthanides (Gd-Er) and negative Eu and positive Tm and Yb anomalies; Group III has an unfractionated pattern at about 20 times chondrites, except for negative Eu and Yb anomalies; Group IV has a relatively unfractionated pattern at 2-4 times chondrites; Group V has an unfractionated pattern at 10-20 times chondrites; Group VI has an unfractionated pattern at 10-20 times chondrites, except for positive Eu and Yb anomalies (i.e., complementary to Group III). The complex patterns of trace element distribution in these Allende inclusions indicate a complex history of formation of this meteorite from the solar nebula.


Field and Laboratory Investigations of Meteorites from Victoria Land, Antarctica
Ursula B. Marvin and Brian Mason, editors
134 pages, 79 figures, 11 tables
1984 (Date of Issue: 8 June 1984)
Number 26, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities in Victoria Land during the 1980-1981 and 1981-1982 field seasons, and the geodetic measurements of ice motion and ablation at the Allan Hills site. Descriptions and classifications are given for all specimens collected during the 1980-1981 season and for most of those collected during the 1981-1982 season. Review articles are included on the petrology and classification of 145 small meteorites collected in the 1977-1978 season, on Antarctic Type 3 chondrites, and on cosmic-ray-produced nuclides in the Victoria Land meteorites. The first lunar meteorite is described. Chemical analyses of 25 Victoria Land meteorites are published, with a discussion of Antarctic weathering effects. The Appendix lists all of the Victoria Land meteorites classified as of June 1983, by numerical order for each locality and by meteorite class.


The Allende Meteorite Reference Sample
Eugene Jarosewich, Roy S. Clarke, Jr. and Julie N. Barrows, editors
49 pages, 32 tables
1987 (Date of Issue: 24 February 1987)
Number 27, Smithsonian Contributions to the Earth Sciences
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Abstract

A reference material for comparative analytical studies and standardization was prepared from fresh, clean specimen material from the Allende, Mexico, Type CV3 carbonaceous chondrite fall of 8 February 1969. Fragments weighing 4 kg were powdered, homogenized, and split into 1 g and 5 g subsamples. Analytical results for a total of 74 elements were provided by 24 analysts or groups of analysts. A variety of techniques were used, and many elements were determined by more than one technique. Reports from contributors of data outline their procedures and give their results in detail. Sample homogeneity has been evaluated in terms of this body of data, and " recommended values" are suggested for 43 elements.


Field and Laboratory Investigations of Meteorites from Victoria Land and the Thiel Mountains Region, Antarctica, 1982-1983 and 1983-1984
Ursula B. Marvin and Glenn J. MacPherson, editors
146 pages, 86 figures, 14 tables
1989 (Date of Issue: 16 February 1989)
Number 28, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities of the United States Antarctic Search for Meteorites (ANSMET) expeditions of the 1982-1983 and 1983-1984 field seasons. Descriptions and classifications are given of most specimens collected during the 1982-1983 season and some of those collected in the 1983-1984 season. Articles are included reviewing topics such as Antarctic achondrites, carbonaceous chondrites, meteorite weathering under polar conditions, trace element contents of Antarctic meteorites in comparison with those found elsewhere, and the meteorite pairing problem. One chapter describes the crystalline fabric of the ice surrounding a meteorite discovered emerging at the surface. The Appendix lists all ANSMET specimens classified as of June 1984, in numerical order for each locality and by meteorite class. The Appendix also includes a tentative list of paired specimens.


Climate and Moisture Variability in a Tropical Forest: Long-term Records from Barro Colorado Island, Panamá
Donald M. Windsor
145 pages, 35 figures, 51 tables
1990 (Date of Issue: 18 December 1990)
Number 29, Smithsonian Contributions to the Earth Sciences
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Abstract

Long-term environmental monitoring results are presented documenting the seasonality experienced by the lowland tropical forest on Barro Colorado Island, Panamá. A dry season has developed during each of the past 62 years, typically starting in late December or early January and ending with the first heavy rains in late April or early May. Solar radiation totals climb during dry seasons to monthly levels 50% higher than normal in the wet season. Average daily maximum temperatures increase by two degrees C while average daily minimum temperatures increase by roughly one degree C. Development of the dry season is accompanied by a doubling in average daily windspeed and a drop of ten percent in average midday relative humidity.

Annual rainfall on Barro Colorado Island averages 2612 mm (1925-1989), 90% of which falls in the months of May through November. Rainfall on Barro Colorado Island and seven other sites in the middle of the isthmus has decreased significantly over time. The only long-term rainfall records without decreasing trend come from coastal sites, suggesting that convective, but not orographic, rainfall, has diminished during the last sixty years. Further, annual rainfall appears to be influenced by factors associated with El Niño events. Higher than normal rainfall tends to occur the year before and lower than normal rainfall tends to occur the year of such events. Dry-season forest and clearing temperatures on Barro Colorado Island were elevated during each of the three El Niño events occurring in the past 16 years.

Storms that drop most of their moisture in a minute or two are common during the wet season on Barro Colorado Island. The soils of Lutz catchment are steep and clay rich. Most moisture in storage resides in the upper 10 cm. Available soil moisture is largely depleted by mid- to late dry season.

Actual evapotranspiration, calculated as the difference between rainfall and runoff and changes in storage for each of 14 years averaged 64 percent of annual rainfall. Eighty-five percent (1534 mm) of annual rainfall was returned directly to the atmosphere as vapor in the dryest of the past 16 years (1976) while only 47% (1953 mm) was returned in the wettest year (1983). Comparison of average evapotranspiration and rainfall characteristics from 18 temperate and tropical hydrological studies suggests a loose positive relationship exists between these two quantities in forested ecosystems.


Field and Laboratory Investigations of Antarctic Meteorites Collected by United States Expeditions, 1985-1987
Ursula B. Marvin and Glenn J. MacPherson, editors
116 pages, 38 figures, 9 tables
1992 (Date of Issue: 18 December 1992)
Number 30, Smithsonian Contributions to the Earth Sciences
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Abstract

This monograph describes the meteorite collecting activities of the United States Antarctic Search for Meteorites (ANSMET) expeditions during the 1984-1985, 1985-1986, and 1986-1987 field seasons. Descriptions and classifications are given of most specimens collected during those expeditions with the exceptions of the types 4, 5, and 6 ordinary chondrites, whose properties are tabulated. Two articles are included that summarize data on the terrestrial ages and thermoluminescence properties of Antarctic meteorites. The Appendix lists all ANSMET specimens classified as of June 1987, in numerical order for each locality and by meteorite class.


Displaying 21 - 30 from the 33 total records