Titre :

Iron valence state of fine-grained material from the Jupiter family comet 81P/Wild 2 - A coordinated TEM / STEM EDS / STXM study

Auteur(s) :

Stodolna, Julien [Auteur]
Space Sciences Laboratory [Berkeley] [SSL]
Gainsforth, Zack [Auteur]
Space Sciences Laboratory [Berkeley] [SSL]
Leroux, Hugues [Auteur]
Unité Matériaux et Transformations - UMR 8207 [UMET]
Butterworth, Anna L. [Auteur]
Space Sciences Laboratory [Berkeley] [SSL]
Tyliszczak, Tolek [Auteur]
Advanced Light Source [LBNL Berkeley] [ALS]
Jacob, Damien [Auteur]
Unité Matériaux et Transformations - UMR 8207 [UMET]
Westphal, Andrew J. [Auteur]
Space Sciences Laboratory [Berkeley] [SSL]

Titre de la revue :

Geochimica et Cosmochimica Acta

Numéro :

122

Pagination :

1-16

Date de publication :

2013

Discipline(s) HAL :

Planète et Univers [physics]/Astrophysique [astro-ph]
Physique [physics]/Matière Condensée [cond-mat]/Science des matériaux [cond-mat.mtrl-sci]
Physique [physics]/Astrophysique [astro-ph]
Planète et Univers [physics]/Sciences de la Terre
Chimie/Matériaux
Physique [physics]/Physique [physics]/Géophysique [physics.geo-ph]

Résumé en anglais : [en]

The oxidation state of transition metal elements is an indicator of the environmental conditions during formation and history of extraterrestrial materials. We studied the iron valence state of fine-grained material from ...
Lire la suite >The oxidation state of transition metal elements is an indicator of the environmental conditions during formation and history of extraterrestrial materials. We studied the iron valence state of fine-grained material from a bulbous track extracted from the Stardust cometary collector. It likely originated from primitive material of the comet Wild 2. We used synchrotron-based Scanning Transmission X-ray Microscopy (STXM) to collect Fe L3-XANES spectra at a spatial resolution of about 20 nm. Maps of Fe valence state were combined with the elemental maps recorded by energy dispersive X-ray spectroscopy (EDS) with a transmission electron microscope (TEM), on the same areas and with a comparable electron probe size (5–20 nm). As for most Stardust fine-grained material, the samples are severely damaged by the hypervelocity impact in the aerogel collector blocks. They show of a wide range of oxidation state at a micrometer scale, from Fe metal to Fe3+. This heterogeneity of oxidation state can be due to the extreme conditions of the collection. Two major parameters can favor changes in redox state. The first is the high temperature regime, known to be highly heterogeneous and to have locally reached extreme values (up to 2000 K). The second is the local chemical environment. It may contain elements that could favor a reduction or oxidation reaction within the flash-heated Wild 2 fragments. Comparison of maps by STXM and EDS shows evidence for several correlation trends between element concentrations and the iron valence state. These observations, together with the study of a melted rim of a larger particle, suggest that the redox state was not completely redistributed within the impact melts. These local signatures are compatible with precursors that could have been close to primitive matrix material of chondrites or to chondritic interplanetary dust particles. On average, the fine-grained material from Wild 2 displays a molar fraction (Fe2+oxide + Fe3+oxide)/(total Fe) equal to 0.80 ± 0.10. It appears more oxidized than the average value measured for the comet, when done on larger particles (Westphal et al., 2009). This fine-grained material from Wild 2 does not seem to have sampled reducing environments in the solar nebulae in contrast with the larger particles of Wild 2. This observation confirms the high degree of diversity of materials in Wild 2 and is in good agreement with the dual distribution of high temperature minerals and matrices in carbonaceous chondrites.Lire moins >

Langue :

Anglais

Comité de lecture :

Oui

Audience :

Internationale

Vulgarisation :

Non

Établissement(s) :

Université de Lille
ENSCL
CNRS
INRA

Collections :

• Unité Matériaux et Transformations (UMET) - UMR 8207

Équipe(s) de recherche :

Matériaux Terrestres et Planétaires

Date de dépôt :

2019-06-03T08:52:37Z
2021-02-17T16:13:54Z