Inner solar system irradiation history of minerals in an ultracarbonaceous Antarctic micrometeorite (UCAMM)

Cecile Engrand (1) , E. Charon (2, 3) , H. Leroux (4) , C. Le Guillou (4) , J. Duprat (5) , E. Dartois (6) , S Bernard (7) , Baptiste Guérin (1) , L. Delauche (1) , M. Godard (1)

1 CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière
2 LEDNA - Laboratoire Edifices Nanométriques
3 NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
4 UMET - Unité Matériaux et Transformations - UMR 8207
5 CSNSM AS - Centre de Sciences Nucléaires et de Sciences de la Matière
6 ISMO - Institut des Sciences Moléculaires d'Orsay
7 IMPMC_COSMO - Cosmochimie [IMPMC]

Introduction: Ultracarbonaceous Antarctic Micrometeorites (UCAMMs) are interplanetary dust particles containing large amounts of N-rich polyaromatic organic matter exhibiting large D enrichments, with heterogeneous distributions of both D/H and 15N/14N isotopic ratios [1-8]. UCAMMs most probably originate from the outer regions of the protoplanetary disk, i.e. the cometary reservoir [2, 4, 5]. At least three kinds of organic matter have been identified in UCAMMs, with different nitrogen abundances and highly variable concentrations of small (typically 30-500 nanometer) minerals embedded in the organic matter [8-11]. The formation process(es) of the different kinds of organic matter found in UCAMMs and the origin of their mixing with minerals are still a matter of debate. We focus here on a mineral assemblage embedded in one UCAMM (DC06-04-43) in which we have found evidence of irradiation. Results and discussion: A 100 nm-thick FIB section was made at IEMN Lille from a fragment of UCAMM DC06-04-43. This section was examined by STXM-XANES followed by transmission electron microscopy (TEM) [11]. The mineralogy of this UCAMM is dominated by a crystalline assemblage consisting of µm-sized Mg-rich pyroxenes, Fe sulfides, Mg-rich olivines, and Fe-Ni metal. GEMS are embedded in the organic matter, close to the crystalline assemblage. We identified irradiation features (rims and tracks) in some crystalline pyroxenes. The rims’ thicknesses range from 20 to 100 nm (average 60 ± 20 nm, 1σ) and irradiation track lengths from 15 nm to ~ 1 µm (average 175 ± 110 nm, 1σ). The average track density is 1.72 x 1010 cm-2 (772 tracks over 4.2 x 106 nm2).

Domaines: Planète et Univers [physics]

Cecile Engrand, E. Charon, H. Leroux, C. Le Guillou, J. Duprat, et al.. Inner solar system irradiation history of minerals in an ultracarbonaceous Antarctic micrometeorite (UCAMM). METSOC 2019 - 82nd Annual Meeting of The Meteoritical Society, 2019, Sapporo, Japan. pp.6415. ⟨hal-02380523⟩