Alteration versus morphology of Antarctic micrometeorites: a simple procedure for sample characterization

• Main Authors: Dobrica, Elena, Engrand, Cecile, Ogliore, R, C, Brearley, A. J.
• Other Authors: Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: [SDU]Sciences of the Universe [physics]; Antarctic; Antarc*
• Online Access: https://hal.science/hal-02380371; https://hal.science/hal-02380371/document; https://hal.science/hal-02380371/file/Dobrica_2019_MMs_alteration_surface-LPSC_1014.pdf

International audience Introduction: About thirty percent of Antarctic micrometeorites (AMMs) collected in surface snow layers near the French-Italian station CONCORDIA are fine-grained (Fg) particles [1-2]. Among the Fg particles, about 20% are fine-grained compact (FgC) and 10% are fine-grained fluffy (FgF) [2]. The description and classification of Fg AMMs as defined in Genge et al. [3] is based on Cap Prudhomme AMMs (collected from blue ice [4]) that do not contain the FgF particles. The FgF AMMs were later identified in the CONCORDIA AMMs collected from snow [2]. Therefore, robust criteria are essential to classify the different types of AMM more definitively. We are exploring the possibility that the surface morphology of AMMs, may be a useful and simple criterion for distinguishing between different types of AMM. Here we present the results of image analysis of Fg AMMs. The purposes of these measurements are (1) to evaluate the surface structure and sample morphology of the Fg AMMs and (2) to determine if there is a relationship between surface structure and the degree of alteration/ primitiveness of the particles. Therefore, the basis of this study is the hypothesis that the surface structure of a fragment reflects the characteristics, e.g. grain size, morphology, and the porosity of the bulk material. Methods: AMMs are split into several fragments of which the smallest is deposited on a stub and characterized by SEM, to ensure its extraterrestrial (ET) nature. Secondary electron images were performed on four AMMs stubs (08-33, 08-34, 11-13, and 14-03) using a FEI Quanta 3D field emission gun (FEG) SEM/FIB operating at 5 kV and 20 kV. On each stub there are between 18 to 42 fragments of AMMs collected from snow during the 2006 campaign [1]. Since the samples were fragmented, the exposed surface does not necessarily represent the external surface during atmospheric entry. The proportion of extraterrestrial particles on each stub vary from 48% ET (stub 11-13) to 94% ET (stub 08-33). Forty-six Fg AMMs ...