Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.596w&link_type=abstract
Meteoritics, vol. 30, no. 5, page 596
Computer Science
4
Ages, Exposure, Carlisle Lakes, Chondrites, R, Rumuruti, Gases, Noble, Solar, Meteorites, Acfer 217, Allan Hills 85151, Pecora Escarpement 91102, Pecora Escarpement 91241, Regolith Breccia
Scientific paper
The former Carlisle-Lakes-like chondrites are now called R-chondrites, named after Rumuruti, the only fall among the 9 members of this group [1,2,3]. We have measured concentration and isotopic composition of noble gases in Rumuruti, Acfer 217, Allan Hills (ALH) 85151, Carlisle Lakes (CL), Pecora Escarpment (PCA) 91002 and 91241 to obtain information on their thermal and exposure history. It was suggested [2] that both PCA meteorites are paired. This is corroborated by their similar noble gas record. Except CL all R-chondrites contain solar noble gases and are thus regolith breccias. This is demonstrated in Fig. 1 where all points fall into a quadrangle formed by the two solar neon components SWC and SEP and the band of cosmogenic neon. The 5 measured samples of ALH85151 form a line which allows the determination of the solar 20Ne/22Ne = 13.0 +/- 0.2 as well as the cosmogenic 22Ne/21Ne = 1.24 +/- 0.03 (assuming a cosmogenic 20Ne/22Ne = 0.83 +/- 0.02). This value is indicative for a small preatmospheric mass of this meteorite. The highest concentration of solar Ne in this meteorite is 5.5 x 10^-5cm^3STP/g and similar to that of several solar gas containing ordinary chondrites. Characteristic for most R-chondrites are rather high values of 129Xe/132Xe. For example, most H-chondrites have values of 1.35 +/- 0.20 while those of R-chondrites are measured between 2.18 and 2.35 (an exception is again CL with a 129Xe/132Xe = 1.27). Production rates of cosmogenic nuclides are calculated from the mean chemical composition of R-chondrites [3] and procedures given in [4]. For 3He, 21Ne and 38Ar production rates (in 10^-8cm^3STP/gMa) are 2.42, 0.281 and 0.041, respectively. Three meteorites (Acfer 217, ALH85151, PCA91002/241) have similar exposure ages in the range of (39 +/- 3) Ma while those of Rumuruti (18 Ma) and CL (7 Ma) are shorter. Figure 1: Neon-isotopic compositions of Rumuruti chondrites. Indicated are the composition of Solar Energetic Particles (SEP) and the Solar Wind (SWC) neon as well as the range of cosmogenic Ne (COS). Except Carlisle Lakes all R-chondrites contain solar gases and are regolith breccias. References: [1] Schulze H. et al. (1994) Meteoritics, 29, 275. [2] Rubin A. E. and Kallemeyn D. W. (1994) Meteoritics, 29, 255. [3] Bischoff et al. (1988) Meteoritics, 29, 264. [4] Eugster O. (1988) GCA, 52, 1649.
Schultz Ludolf
Weber Harald W.
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