Characterization of antarctic meteorites Meteorite studies ...
Characterization of antarctic meteorites BRIAN MASON and Roy S. CLARKE, JR. Department of Mineral Sciences Smithsonian Institution Washington, D.C. 20560
We have continued to characterize antarctic meteorites collected in Victoria Land by W. A. Cassidy (principal investigator) and his colleagues during the 1980-1981 and 1981-1982 field seasons. This work has required the preparation of several hundred polished thin sections of the meteorites, their examination with petrographic and metallographic microscopes, and analysis of the minerals with an electronheam microprobe. Individual meteorites are classified by mineral compositions and textural relationships. Meteorites are classified into four groups: (1) chondritesstony meteorites containing chondrules, which are rounded aggregates of silicate minerals, usually 0.2-2 millimeters in diameter; (2) achondrites—stony meteorites without chondrules; (3) stony-irons—meteorites consisting of subequal amounts of silicate minerals and nickel-iron; and (4) irons—meteorites consisting essentially of a nickel-iron alloy, the nickel content usually in the 5- to 20-percent range. Chondrites, which make up
Meteorite studies: Terrestrial and extraterrestrial applications MICHAEL E. LIPSCHUTZ Department of Chemistry Purdue University West Lafayette, Indiana 47907
The accidental discovery of numerous meteorites on blue-ice in Queen Maud Land by Japanese glaciologists beginning in 1969 prompted the extremely successful search for meteorites in Victoria Land and elsewhere (Reuning 1981). The meteorite search has returned about 1,300 specimens from the 1976-1977 through 1982-1983 field seasons. These specimens are being characterized then released to be studied by well over 100 research groups in 14 countries. Characterization includes estimation of terrestrial alteration: relatively unweathered and unfractured samples are classed as "A-A" while heavily weathered and fractured ones are classed as "C-C". In our laboratory, we use radiochemical neutron activation analysis and atomic absorption spectrometry to determine 11-16 siderophile, chalcophile, lithophile, and volatile/mobile trace elements (measured in parts per million or parts per trillion levels) 1983 REVIEW
by far the most common meteorite group, are subdivided into classes according to increasing iron content of the pyroxene: enstatite (E) chondrites; olivine-bronzite (H) chondrites; olivinehypersthene (L and LL) chondrites; and carbonaceous (C) chondrites, a separate small group characterized by a matrix containing carbonaceous material. Textural relationships are indicated by a digit following the class letter. The 1980-1981 collection has been completely characterized (Mason and Clarke 1982). From the Allan Hills 32 meteorite specimens were collected, 67 from the Reckling Peak area, and 1 near Outpost Nunataks. These specimens have been classified as follows: irons, 2; mesosiderites, 4; eucrites, 3; ureilite, 1; and chondrites, 90. The chondrites belong to the following classes and types: 0, 1; H3, 2; H4, 7; H5, 25; H6, 18; L3, 3; L4, 2; L5, 3; L6, 22; LL5, 2; LL6, 4; and E5, 1. One hundred and forty-five meteorites from the 1981-1982 collection have been characterized, with the following results: irons, 2; mesosiderites, 2; eucrites, 8; ureilte, 1; anorthositic breccia (probably lunar), 1; and chondrites, 131. The chondrites belong to the following classes and types: C2, 2; C3, 1; H4, 26; H5, 48; H6, 20; L3, 9; L4, 2; L5, 4; L6, 9; LL3, 7; LL5, 1; LL6, 1; and E6, 1.
Reference Mason, B., and R. S. Clarke, Jr. 1982. Characterization of the 1980-81 Victoria Land meteorite collections. Memoirs of the National Institute of Polar Research (Tokyo), Special Issue 25, 17-33.
in antarctic meteorites. The results enable us to use meteorites as probes both of extraterrestrial processes and of terrestrial weathering, and thus obtain information about ice-sheet dynamics. In April 1982, a workshop was held to examine the overlap between antarctic glaciology and meteorites. Representatives of both academic communities-36 participants in all—attended. In addition to summarizing the discussions, the report (Bull and Lipschutz 1982) made many recommendations. These may be categorized into five topics: (1) initiating remote reconnaissance to identify blue-ice areas; (2) conducting further meteorite search and glaciology study in additional blue-ice areas; (3) conducting detailed studies of the Allan Hills area of Victoria Land as a prototype system; (4) collecting and studying additional meteorites; (5) improving communication and interaction between meteoriticists, glaciologists, and other scientists. Many of these recommendations are currently being carried out. Previous studies (Biswas, Ngo, and Lipschutz 1980; Biswas et al. 1981) demonstrated that, using proper precautions, antarctic meteorites of weathering/fracturing types A and B yield trace element data as reliable as those determined from non-antarctic falls (cf. Lipschutz 1982). What is unknown is the point at which terrestrial alteration renders antarctic meteorites unsuitable for trace element study: this question is currently under investigation in our laboratory. 87
Antarctic meteorites are just beginning to demonstrate their utility as probes of extraterrestrial objects and processes. Verkouteren and Lipschutz (in preparation) found from trace element studies (silver, arsenic, gold, bismuth, cadmium, cobalt, cesium, gallium, indium, rubidium, antimony, selenium, tellurium, thallium, and zinc) that F chondrites, hitherto found only as inclusions in the Cumberland Falls enstatite achondrite, also exist as inclusions in the antarctic enstatite achondrite Allan Hills 78113. This newly discovered type of primitive meteorite should shed further light on the formation of solid objects in the early solar system. A sample receiving special attention during the past year was Allan Hills 81005 in which Verkouteren, Dennison, and Lipschutz (in preparation) determined siderophilic arsenic, gold, cobalt, gallium, and antimony; volatile/mobile silver, bismuth, cadmium, indium, selenium, tellurium, thallium, and zinc; and lithophilic calcium, rubidium, and uranium. Data for Allan Hills 81005 are similar to those for lunar highlands samples returned by Apollo missions, indicating that this meteorite originated on the moon. Five elements (cobalt, gallium, and lithophiles) reflect lunar crustal processes while the remaining 11 siderophile and volatile/mobile elements (including highly mobile thallium, silver, and cadmium) indicate 1.39 ± 0.54 percent micrometeorite (type 1 carbonaceous chondrite equivalent) admixture or enrichment by thermal mobilization on the Moon (figure). In contrast to L chondrites, where severe
12x
S
2 CL)
HH
0
0
• • T
10-2-
Au As Sb Go Se Te Bi In Ag Zn TI Cd Rb Cs U
Trace element contents of Allan Hills 81005 normalized to those of type 1 carbonaceous chondrites. Vertical lines indicate ±1 sample standard deviation derived from the duplicate analyses. Gallium, cobalt, cesium, rubidium, and uranium probably reflect anorthosite; other elements indicate 1-2 percent (type 1 carbonaceous chondrite) admixture by meteoritic matter, possibly coupled with slight thermal redistribution of very mobile cadmium. These are features often seen in Apollo lunar samples, indicating Allan Hills 81005 was compositionally unaffected during lunar launch and transit to Earth. (Other elements are gold, arsenic, antimony, selenium, tellurium, boron, indium, silver, zinc, thallium, and cesium.)
88
shock effects are common, trace element data indicate that impact-launching of Allan Hills 81005 to Earth was free of substantial ( 20 gigapascals shock loading: this agrees with pressure estimates from mineralogic characteristics of the sample. In this light, a Martian origin for the more severely shocked shergottite, nakhlite, and chassigny (sNc) meteorites is plausible. Because of several suggestions that the 8 SNC meteorites derive from Mars (e.g. McSween et al. 1979), we measured the same 16 elements in the 4 shergottites [including Allan Hills 77005 and both lithologies of Elephant Moraine (76°11'S 157°10'E) 79001] as in Allan Hills 81005. For completeness, we combined our data with those for 31 additional major, minor, and refractory trace elements in the shergottites in a single publication (Smith et al. in preparation). While each shergottite lithology exhibits unique features indicative of a unique source, all sources fractionated from a single primitive magma—hence from a dynamic planet not unlike the Earth. The well established chemical, isotopic, petrologic, and mineralogic properties of the shergottites, in particular, and similar less well established properties of nakhlites and chassigny are consistent with a Martian origin. This research was supported by National Science Foundation grant DPP 81-11513. References Biswas, S., H. T. Ngo, and M. E. Lipschutz. 1980. Trace element contents of selected antarctic meteorites—I. Weathering affects and ALH A77005, A77257, A77278 and A77299. Zeitschrift für Naturforschung, 35a, 191-196. Biswas, S., T. M. Walsh, H. T. Ngo, and M. E. Lipschutz. 1981. Trace element contents of selected antarctic meteorites-11. Comparison with non-antarctic specimens. Proceedings of the Sixth Symposium on Antarctic Meteorites, (19-20 February, National Institute of Polar Research, Tokyo), 221-228. Bull, C. B. B., and M. E. Lipschutz. 1982. Workshop on antarctic glaciology and meteorites. Lunar and Planetary Institute Technical Report 82-03, Houston, Tex.: Lunar and Planetary Institute. Lipschutz, M. E. 1982. Weathering effects in antarctic meteorites. In U. B. Marvin and B. Mason (Eds.), Catalog of Meteorites front Land, Antarctica 1978-1980, Smithsonian Contributions to the Earth Sciences, 24. Washington, D.C.: Smithsonian Institution. McSween, H. Y., Jr., F. M. Stolper, R. A. Muntean, C. D. O'Kelley, J. S. Eldridge, S. Biswas, H. T. Ngo, and M. F. Lipschutz. 1979. Evidence for a petrogenetic relationship between the Allan Hills 77005 achondrite and the shergottites. Earth and Planetary Science Letters 45, 275-284. Reuning, W. M. 1981. Antarctic meteorites provide new data. Antarctic Journal of the U.S., 16(2), 1-4. Smith, M. R., J . C. Laul, M.-S. Ma, T. J . Huston, R. M. Verkouteren, M. E. Lipschutz, and R. A. Schmitt. In preparation. Petrogenesisof the SNC (shergottites, nakhlites and chassignites) meteorites: Implications for their origin from a large dynamic planet, possibly Mars, Proceedings of the Fourteenth Lunar and Planetary Science Conference. 14-18 March, Johnson Space Center, Houston, Tex. Verkouteren, R. M., and M. E. Lipschutz. In preparation. Cumberland Falls chondritic inclusions--Il. Trace element contents of forsterite chondrites and meteorites of similar redox state. Geochimica et Cosmochimica Acta. Verkouteren, R. M., J . E. Dennison, and M. E. Lipschutz. In preparation. Siderophile, lithophile and mobile trace elements in the lunar meteorite Allan Hills 81005. Geophysical Research Letters.
ANTARCTIC JOURNAL
We have continued to characterize antarctic meteorites collected in Victoria Land by W. A. Cassidy (principal investigator) and his colleagues during the 1980-1981 and 1981-1982 field seasons. This work has required the preparation of several hundred polished thin sections of the meteorites, their examination with petrographic and metallographic microscopes, and analysis of the minerals with an electronheam microprobe. Individual meteorites are classified by mineral compositions and textural relationships. Meteorites are classified into four groups: (1) chondritesstony meteorites containing chondrules, which are rounded aggregates of silicate minerals, usually 0.2-2 millimeters in diameter; (2) achondrites—stony meteorites without chondrules; (3) stony-irons—meteorites consisting of subequal amounts of silicate minerals and nickel-iron; and (4) irons—meteorites consisting essentially of a nickel-iron alloy, the nickel content usually in the 5- to 20-percent range. Chondrites, which make up
Meteorite studies: Terrestrial and extraterrestrial applications MICHAEL E. LIPSCHUTZ Department of Chemistry Purdue University West Lafayette, Indiana 47907
The accidental discovery of numerous meteorites on blue-ice in Queen Maud Land by Japanese glaciologists beginning in 1969 prompted the extremely successful search for meteorites in Victoria Land and elsewhere (Reuning 1981). The meteorite search has returned about 1,300 specimens from the 1976-1977 through 1982-1983 field seasons. These specimens are being characterized then released to be studied by well over 100 research groups in 14 countries. Characterization includes estimation of terrestrial alteration: relatively unweathered and unfractured samples are classed as "A-A" while heavily weathered and fractured ones are classed as "C-C". In our laboratory, we use radiochemical neutron activation analysis and atomic absorption spectrometry to determine 11-16 siderophile, chalcophile, lithophile, and volatile/mobile trace elements (measured in parts per million or parts per trillion levels) 1983 REVIEW
by far the most common meteorite group, are subdivided into classes according to increasing iron content of the pyroxene: enstatite (E) chondrites; olivine-bronzite (H) chondrites; olivinehypersthene (L and LL) chondrites; and carbonaceous (C) chondrites, a separate small group characterized by a matrix containing carbonaceous material. Textural relationships are indicated by a digit following the class letter. The 1980-1981 collection has been completely characterized (Mason and Clarke 1982). From the Allan Hills 32 meteorite specimens were collected, 67 from the Reckling Peak area, and 1 near Outpost Nunataks. These specimens have been classified as follows: irons, 2; mesosiderites, 4; eucrites, 3; ureilite, 1; and chondrites, 90. The chondrites belong to the following classes and types: 0, 1; H3, 2; H4, 7; H5, 25; H6, 18; L3, 3; L4, 2; L5, 3; L6, 22; LL5, 2; LL6, 4; and E5, 1. One hundred and forty-five meteorites from the 1981-1982 collection have been characterized, with the following results: irons, 2; mesosiderites, 2; eucrites, 8; ureilte, 1; anorthositic breccia (probably lunar), 1; and chondrites, 131. The chondrites belong to the following classes and types: C2, 2; C3, 1; H4, 26; H5, 48; H6, 20; L3, 9; L4, 2; L5, 4; L6, 9; LL3, 7; LL5, 1; LL6, 1; and E6, 1.
Reference Mason, B., and R. S. Clarke, Jr. 1982. Characterization of the 1980-81 Victoria Land meteorite collections. Memoirs of the National Institute of Polar Research (Tokyo), Special Issue 25, 17-33.
in antarctic meteorites. The results enable us to use meteorites as probes both of extraterrestrial processes and of terrestrial weathering, and thus obtain information about ice-sheet dynamics. In April 1982, a workshop was held to examine the overlap between antarctic glaciology and meteorites. Representatives of both academic communities-36 participants in all—attended. In addition to summarizing the discussions, the report (Bull and Lipschutz 1982) made many recommendations. These may be categorized into five topics: (1) initiating remote reconnaissance to identify blue-ice areas; (2) conducting further meteorite search and glaciology study in additional blue-ice areas; (3) conducting detailed studies of the Allan Hills area of Victoria Land as a prototype system; (4) collecting and studying additional meteorites; (5) improving communication and interaction between meteoriticists, glaciologists, and other scientists. Many of these recommendations are currently being carried out. Previous studies (Biswas, Ngo, and Lipschutz 1980; Biswas et al. 1981) demonstrated that, using proper precautions, antarctic meteorites of weathering/fracturing types A and B yield trace element data as reliable as those determined from non-antarctic falls (cf. Lipschutz 1982). What is unknown is the point at which terrestrial alteration renders antarctic meteorites unsuitable for trace element study: this question is currently under investigation in our laboratory. 87
Antarctic meteorites are just beginning to demonstrate their utility as probes of extraterrestrial objects and processes. Verkouteren and Lipschutz (in preparation) found from trace element studies (silver, arsenic, gold, bismuth, cadmium, cobalt, cesium, gallium, indium, rubidium, antimony, selenium, tellurium, thallium, and zinc) that F chondrites, hitherto found only as inclusions in the Cumberland Falls enstatite achondrite, also exist as inclusions in the antarctic enstatite achondrite Allan Hills 78113. This newly discovered type of primitive meteorite should shed further light on the formation of solid objects in the early solar system. A sample receiving special attention during the past year was Allan Hills 81005 in which Verkouteren, Dennison, and Lipschutz (in preparation) determined siderophilic arsenic, gold, cobalt, gallium, and antimony; volatile/mobile silver, bismuth, cadmium, indium, selenium, tellurium, thallium, and zinc; and lithophilic calcium, rubidium, and uranium. Data for Allan Hills 81005 are similar to those for lunar highlands samples returned by Apollo missions, indicating that this meteorite originated on the moon. Five elements (cobalt, gallium, and lithophiles) reflect lunar crustal processes while the remaining 11 siderophile and volatile/mobile elements (including highly mobile thallium, silver, and cadmium) indicate 1.39 ± 0.54 percent micrometeorite (type 1 carbonaceous chondrite equivalent) admixture or enrichment by thermal mobilization on the Moon (figure). In contrast to L chondrites, where severe
12x
S
2 CL)
HH
0
0
• • T
10-2-
Au As Sb Go Se Te Bi In Ag Zn TI Cd Rb Cs U
Trace element contents of Allan Hills 81005 normalized to those of type 1 carbonaceous chondrites. Vertical lines indicate ±1 sample standard deviation derived from the duplicate analyses. Gallium, cobalt, cesium, rubidium, and uranium probably reflect anorthosite; other elements indicate 1-2 percent (type 1 carbonaceous chondrite) admixture by meteoritic matter, possibly coupled with slight thermal redistribution of very mobile cadmium. These are features often seen in Apollo lunar samples, indicating Allan Hills 81005 was compositionally unaffected during lunar launch and transit to Earth. (Other elements are gold, arsenic, antimony, selenium, tellurium, boron, indium, silver, zinc, thallium, and cesium.)
88
shock effects are common, trace element data indicate that impact-launching of Allan Hills 81005 to Earth was free of substantial ( 20 gigapascals shock loading: this agrees with pressure estimates from mineralogic characteristics of the sample. In this light, a Martian origin for the more severely shocked shergottite, nakhlite, and chassigny (sNc) meteorites is plausible. Because of several suggestions that the 8 SNC meteorites derive from Mars (e.g. McSween et al. 1979), we measured the same 16 elements in the 4 shergottites [including Allan Hills 77005 and both lithologies of Elephant Moraine (76°11'S 157°10'E) 79001] as in Allan Hills 81005. For completeness, we combined our data with those for 31 additional major, minor, and refractory trace elements in the shergottites in a single publication (Smith et al. in preparation). While each shergottite lithology exhibits unique features indicative of a unique source, all sources fractionated from a single primitive magma—hence from a dynamic planet not unlike the Earth. The well established chemical, isotopic, petrologic, and mineralogic properties of the shergottites, in particular, and similar less well established properties of nakhlites and chassigny are consistent with a Martian origin. This research was supported by National Science Foundation grant DPP 81-11513. References Biswas, S., H. T. Ngo, and M. E. Lipschutz. 1980. Trace element contents of selected antarctic meteorites—I. Weathering affects and ALH A77005, A77257, A77278 and A77299. Zeitschrift für Naturforschung, 35a, 191-196. Biswas, S., T. M. Walsh, H. T. Ngo, and M. E. Lipschutz. 1981. Trace element contents of selected antarctic meteorites-11. Comparison with non-antarctic specimens. Proceedings of the Sixth Symposium on Antarctic Meteorites, (19-20 February, National Institute of Polar Research, Tokyo), 221-228. Bull, C. B. B., and M. E. Lipschutz. 1982. Workshop on antarctic glaciology and meteorites. Lunar and Planetary Institute Technical Report 82-03, Houston, Tex.: Lunar and Planetary Institute. Lipschutz, M. E. 1982. Weathering effects in antarctic meteorites. In U. B. Marvin and B. Mason (Eds.), Catalog of Meteorites front Land, Antarctica 1978-1980, Smithsonian Contributions to the Earth Sciences, 24. Washington, D.C.: Smithsonian Institution. McSween, H. Y., Jr., F. M. Stolper, R. A. Muntean, C. D. O'Kelley, J. S. Eldridge, S. Biswas, H. T. Ngo, and M. F. Lipschutz. 1979. Evidence for a petrogenetic relationship between the Allan Hills 77005 achondrite and the shergottites. Earth and Planetary Science Letters 45, 275-284. Reuning, W. M. 1981. Antarctic meteorites provide new data. Antarctic Journal of the U.S., 16(2), 1-4. Smith, M. R., J . C. Laul, M.-S. Ma, T. J . Huston, R. M. Verkouteren, M. E. Lipschutz, and R. A. Schmitt. In preparation. Petrogenesisof the SNC (shergottites, nakhlites and chassignites) meteorites: Implications for their origin from a large dynamic planet, possibly Mars, Proceedings of the Fourteenth Lunar and Planetary Science Conference. 14-18 March, Johnson Space Center, Houston, Tex. Verkouteren, R. M., and M. E. Lipschutz. In preparation. Cumberland Falls chondritic inclusions--Il. Trace element contents of forsterite chondrites and meteorites of similar redox state. Geochimica et Cosmochimica Acta. Verkouteren, R. M., J . E. Dennison, and M. E. Lipschutz. In preparation. Siderophile, lithophile and mobile trace elements in the lunar meteorite Allan Hills 81005. Geophysical Research Letters.
ANTARCTIC JOURNAL
