Baecker B

Cartwright JA

Cordier C

FOLCO, LUIGI

Ott U.

Trieloff M

English

Archivio della Ricerca - Università di Pisa

NOBLE GASES IN COSMIC SPHERULES AND MICROMETEORITES FROM THE TRANSANTARCTIC MOUNTAINS. B. Baecker1, C. Cordier2, L. Folco2, M. Trieloff3, J. A. Cartwright1 and U. Ott1. 1Max Planck Institute for Chemistry, Joh.-J.-Becher-Weg 27, D-55128 Mainz, Germany. E-mail: b.baecker@mpic.de. ²MNA, Siena, Italy. ³University of Heidelberg, Germany.  Introduction: At MPI Mainz we have initiated a comprehen-sive survey of noble gases in micrometeorites. While He and Ne in micrometeorites are generally dominated by solar contribu-tions, the inventory of heavy primordial noble gases is not as well characterized. We hope to fill this gap with particular focus on the diagnostic isotopic composition of Xe. While our study will even-tually include material from a variety of collections (e.g. the CONCORDIA collection [1]), our first results are from “large” PNRA (Programma Nazionale delle Ricerche in Antartide, Italy) micrometeorites collected from the Victoria Land, Transantarctic Mountain micrometeorite traps [2]. Samples and Analytics: 51 micrometeorites (MM´s) - 26 cosmic spherules (CS), 11 scoriaceous (Sc), 14 unmelted (Un) - in the 600-800 µm size range were extracted from traps #45 b and c on the top of Miller Butte, and split into aliquots for combined petrographic and noble gas analyses. For the latter, aliquots were heated using a CO2 laser. The analyses were performed using our multicollector Nu Instruments noble gas mass spectrometer [3]. Preliminary Results: At present, we have obtained noble gas results for three CS and one Sc micrometeorites. Our Ne and Ar results (corrected for isobaric interferences, but not extraction blank) are listed in Table 1. Table 1. Ne and Ar results for MM´s. Sizes are given in µm. Weights are given in µg, noble gas amounts - not corrected for blank - in 10-12 cc units. Uncertainties in the last digits. Sample Size Weight 22Ne 20Ne/22Ne 21Ne/22Ne 36Ar 40Ar/36Ar CS 45c21 720 x 556 337.9 0.41 9.11 (37) 0.029 (2) 0.40 319 (17) CS 45c17 630 x 476 126.3 0.16 9.34 (1.01) 0.038 (6) 2.36 280 (9) CS 45c16 465 x 324 105.1 0.21 8.85 (85) 0.027 (4) 0.98 292 (10) Sc 45b22 268 x 191 9.2 0.49 10.46 (45) 0.062 (4) 1.04 128 (5) As found in previous studies (e.g. [4, 5]) noble gas abun-dances in CS are mostly low and essentially have a terrestrial air signature (e.g. 20Ne/22Ne ~9.8, 21Ne/22Ne ~0.029). In contrast, the Sc micrometeorite shows 20Ne/22Ne and (even clearer) 21Ne/22Ne ratios higher than air, indicative of the presence of solar and spal-logenic Ne. Using the production rates for IDPs from table 3 in [6], the spallogenic 21Ne of ~1.6 x 10-9 cc/g would be produced at 1 AU by SCR primaries in ~0.17 Ma, for production by GCR pri-maries, the inferred exposure would be ~ 4 Ma. The concentration of trapped (solar) 20Ne of ~5 x 10-7 cc/g is about an order of mag-nitude lower than the geometric mean for Un micrometeorites from Yamato Mountains and Dome Fuji, but distinctly higher than in CS (see table 4 in [4]). The low 40Ar/36Ar ratio for the Sc micrometeorite (~128) indicates the presence of trapped 36Ar, at an abundance of ~6 x 10-8 cc/g. This is most likely “planetary” type Ar, carried primarily by phase Q [7]. Acknowledgments: We acknowledge support by DFG through SPP 1385 (Project OT 171/5-1) and PNRA. References: [1] Duprat J. et al. (2007) Advances in Space Research 39:605-611. [2] Rochette P. et al. (2008) Proceedings of the National Academy of Sciences 105:18206-18211. [3] Ott U. et al. (2010) Meteoritics & Planetary Science 45:A158. [4] Osawa T. et al. (2010) Meteoritics & Planetary Science 45:1320-1339 [5] Marty B. et al. (2005) Meteoritics & Planetary Science 40:881-894. [6] Kehm K. et al. (2006) Meteoritics & Planetary Science 41:1199-1217. [7] Lewis R. S. et al. (1975) Science 190:1251-1262. 74th Annual Meteoritical Society Meeting (2011) 5083.pdf

NOBLE GASES IN COSMIC SPHERULES AND MICROMETEORITES FROM THE TRANSANTARCTIC MOUNTAINS

https://arpi.unipi.it/bitstream/11568/148575/1/Baecker_5083_2012.pdf

NOBLE GASES IN COSMIC SPHERULES AND MICROMETEORITES FROM THE TRANSANTARCTIC MOUNTAINS

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