A silicate inclusion in Puente del Zacate, a IIIA iron meteorite

Science

Volumn 273, Issue 5280, 1996, Pages 1365-1367

  Olsen, Edward J ^a   Davis, Andrew M ^b   Clayton, Robert N ^a,c   Mayeda, Toshiko K ^b   Moore, Carleton B ^d   Steele, Lan M ^a  

^a UNIVERSITY OF CHICAGO   (United States)

^b UNIVERSITY OF CHICAGO   (United States)

^c UNIVERSITY OF CHICAGO   (United States)

^d ARIZONA STATE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CHROMIUM DERIVATIVE; GRAPHITE; IRON DERIVATIVE; MINERAL;

ARTICLE; CHEMICAL ANALYSIS; CHEMICAL COMPOSITION; METEOROLOGY; MICROANALYSIS; PRIORITY JOURNAL; ROCK;

IRON METEORITE; ISOTOPIC COMPOSITION; OXYGEN; PETROLOGY; PUENTE DEL ZACATE METEORITE; SILICATE INCLUSION;

EID: 0029659881     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.273.5280.1365     Document Type: Article

References (23)

1. Arizona State University specimen 94b. The IIIA classification of a metal sample collected from this specimen was confirmed by J. T. Wasson of the University of California, Los Angeles. Composition (in parts per million): Ga, 19; As, 4.8; and Ir, 1.2.
2. Collectively called IIIAB.
3. E. Olsen and K. Fredriksson, Geochim. Casmochim. Acta 30, 459 (1966); E. Olsen and I. Steele, Meteoritics 28, 415 (1993); Lunar Planet. Sd. XXV, 1025 (1994),
4. E. Olsen and K. Fredriksson, Geochim. Casmochim. Acta 30, 459 (1966); E. Olsen and I. Steele, Meteoritics 28, 415 (1993); Lunar Planet. Sd. XXV, 1025 (1994),
5. E. Olsen and K. Fredriksson, Geochim. Casmochim. Acta 30, 459 (1966); E. Olsen and I. Steele, Meteoritics 28, 415 (1993); Lunar Planet. Sd. XXV, 1025 (1994),
6. To preserve this scarce material, we performed the entire study on a 4 mm by 4 mm chip from an exposed saw-cut surface, prepared as a polished (thick) section, and from a small chip removed for oxygen isotope analysis. No thin section was made because that would have caused loss of material and reduced the section's area.
7. Granoblastic texture consists of approximately equidimensional crystals with well-sutured boundaries.
8. Analyses were performed on a Cameca SX-50 electron probe microanalyzer (15 kV, 25 nA); we analyzed natural and synthetic standards with online PAP corrections.
9. We analyzed 309 scanned areas each measuring 100 μm on a side. This size area violates the electron beam geometry used to calculate the standard analytical corrections. To estimate the error, we analyzed several such areas covering monominerallic silicate phases; the relative errors were within ± 10% for each element for the same minerals analyzed by a 2-μm-spot beam. The 309 analyses covered about one-fourth of the section's area. Many analyses gave low totals because of cavities or graphite (the instrument does not detect carbon). The averaged results gave 27 weight % pore space, in good agreement with the point count; we shall assume that this percentage represents original graphite. The whole-rock analysis in Table 1 used the averaged values of the 309 analyses, an average that could vary relatively by ± 10% for each element analyzed.
10. Ion microprobe data were collected with an Associated Electrical Industries (AEI) IM-20 ion microprobe using magnetic peak switching at low mass resolution (M/ΔM = 500) Molecular interferences were suppressed by energy filtering. Calcium-normalized ion yields and interferences were determined from a variety of silicate minerals and glasses. E. Zinner and G. Crozaz , Int. J. Mass Spectrom. Ion Processes 69, 17 (1986).
11. Chondrites are primitive meteorites that contain small spherules, called chondrules, and appear to have been produced very early in the formation of the solar system. The C1 chondrites are the most primitive, and chemical data are commonly normalized to their composition.
12. Pallasites and mesosiderites are stony iron meteorites consisting of silicate masses contained in a matrix of Fe-Ni metal. Pallasites are considered to have comprised the boundary between the core and the mantle of asteroid bodies.
13. Basaltic achondrites (collectively called HED) are stony meteorites that have undergone complex igneous histories; eucrites bear a resemblance to terrestrial basalt lavas.
14. R, Clayton, Annu. Rev. Earth Planet Sci. 21, 115 (1993).
15. T. Bunch er al., Contrib. Mineral. Petrol. 25, 297 (1970).
16. Siderophile elements are those that alloy in Fe-Ni metal.
17. B.-G. Choi et al, Geochim. Cosmochim. Acta 59, 593 (1995).
18. A. Kracher, Proc. Lunar Planet. Sci. Conf. 15, C689 (1985).
19. A. Meibom et al., Meteoritics 30, 544 (1995).
20. V. F. Buchwald, Handbook of Iron Meteorites (Univ. of California Press, Berkeley, 1975).
21. Cohenite is an Fe-Ni carbide mineral.
22. The REE content of olivine is so low that its contribution to the whole rock composition is negligible.
23. We thank J. T. Wasson for analyzing this PDZ metal to confirm its IIIA classification, E. R. D. Scott for a helpful discussion, R. Schmitt for a noble attempt to analyze a vanishingly small flake of PDZ, and two anonymous referees who added stimulating ideas and improved this report immeasurably. This work was supported by NASA grants NAGW-3569 (E.J.O.), NAGW-3384 (A.M.D.), and NAGW 3416 (I.M.S.) and NSF grants EAR 92-18857 (R.N.C.), EAR-9303530 (I.M.S.), and EAR-9316062 (I.M.S.).