Preirradiation history of Djermaia (H) chondritic breccia |
| |
| Authors: | JC Lorin P Pellas |
| |
| Institution: | Laboratoire de “Minéralogie des roches profondes et des météorites” du Muséum National d''Histoire Naturelle associé au C.N.R.S.(LA no. 286), 61, rue Buffon, 75005 Paris, France |
| |
| Abstract: | Djermaia is a unique case among gas-rich chondrites. Twelve light xenoliths studied so far in the two available stones show unequivocal evidences of large preirradiation effects, which stand out most clearly when both cosmic-ray track and spallogenic rare-gas data are considered and compared to data from chondrites with a simple radiation history. Each of the two stones studied displays a specific xenolith population with distinct morphological and preirradiation characteristics. The first population consists of rounded and more- or less-shocked xenoliths which show evidences of short solar-flare irradiation (<1 my) and a longer residence under heavier shielding (～50 g/cm2). The second population shows neither clear indication of surface erosion nor evidence of solar-flare effects, and its preirradiation occured in deep-seated locations (～150 g/cm2).The size distribution of xenoliths is also different for the two populations, indicative of more active reworking processes in the top ～20 cm of the Djermaia regolith than at a depth of ～50 cm. The amount of 21Nesp accumulated during the preirradiation stage is substantial (25–60% of total 21Nesp), corresponding to a formal preexposure time of ～15 my for both stones, assuming static irradiation conditions. These results give an insight into the dynamics of the upper levels of the H-asteroid regolith, which appears to be in good agreement with the model of Housen, Wilkening, Chapman, and Greenberg (Icarus, 1979, 39, 317–351). |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
