E01-JEM ARM 200CF
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Open Access
Abstract: An understanding the organic matter (OM) in primitive interplanetary materials can provide us with important constraints on both the early solar system carbon cycle and incipient prebiotic synthesis before the origin of life. As a window to the past, primitive chondrites preserve the most pristine record of parent body, nebular and interstellar components and the occurrence of OM in them has been shown in both soluble (SOM) (1) and insoluble (IOM) (2) form. Total organic carbon (TOC) abundance reaches ~3-4 wt% in the most primitive carbonaceous chondrite (CCs) (3), such as Ivuna-type chondrites (CIs) – thus making them highly desirable for the OM studies, and relevant to the study of Asteroid 162173 Ryugu samples from the Hayabusa-2 mission.
A combination of both SOM and IOM analysis of organic bulk meteorite separates together with in-situ analysis of OM have provided a comprehensive account of chondritic OM (4). In the case of in-situ analysis, the combination of both scanning (SEM) and transmission electron microscopy (TEM) together with soft X-Ray scanning transmission microscopy (STXM) have shown the presence of micron to submicron distinctive organic particles (OPs) (5). Carbon K-edge X-ray absorption near edge structure (XANES) has shown the aromatic-carbonyl-carboxyl chemical nature of these organic particles (5). In addition, aromatic-poorer and carboxylic-richer diffuse OM (6) within both amorphous and phyllosilicate occurs as well.
As observation techniques are getting better, aberration corrected TEM coupled with electron energy loss spectroscopy (EELS) might provide the same results as carbon XANES, but with higher image magnification, rapid data acquisition and better accessibility. In this context, we present the results of a comparative carbon K-edge XANES and EELS study of CI meteorite Ivuna. An approximately 100 nm lamella of the Ivuna meteorite was prepared using focused ion beam (FIB)-SEM with the Helios 5 Hydra DualBeam (CEITEC, Masaryk University, Czechia) and analysed by TEM-EELS with the JEOL ARM200CF (ePSIC, Diamond Light Source, UK) and STXM-XANES at Beamline BL19A of the KEK Photon Factory, Japan. We observed that (I) XANES on samples that did not experience TEM-EELS are in agreement with the previous studies of aromatic-carbonyl-carboxylic macromolecular OPs and IOM, while (II) the TEM-EELS of OPs show aromatic-carbonyl functional chemistry but with amorphous carbon convoluting the carboxylic peak, and aromatic-poor spectra with a sharp carbonate peak in diffuse OM. The difference between XANES and EELS particularly in the diffuse OM can be interpreted by electron-beam damage. Thickness and e-beam damage leads to amorphous C formation in the OPs. In the case of more labile OM in the phyllosilicate, its change by heating and oxidation is expected.
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Feb 2023
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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Open Access
Abstract: Phyllosilicate minerals in the carbonaceous chondrites provide insights into processes in primitive parent bodies of the early Solar System. It is widely agreed that the CM- and CI-type carbonaceous chondrites underwent aqueous alteration on their parent bodies, resulting in phyllosilicate-rich matrices, where the dominant mineral phase is serpentine. There are many previous studies investigating phyllosilicate structure in carbonaceous chondrites, however, the presence of sulfur in these minerals and its effect on crystal lattice structure has not been studied in detail. We are investigating how the presence of sulfur (up to ≃9-10 wt% SO3) in serpentine phyllosilicate regions effects basal lattice spacing measurements of serpentine-like minerals in CM- and CI-type chondritic and related asteroidal material.
Four specimens are being studied for this work: Winchcombe and Aguas Zarcas (CM-type), and Ryugu samples (A0058-C2001-08, A0104-00200502 and A0104-01700602) from Hayabusa2 and Ivuna (CI-type). All samples are TEM wafers. We have used a multi-technique approach to study the samples, with the E01 JEOL ARM200CF and E02 JEOL ARM300CF electron microscopes at the ePSIC facility at Diamond Light Source in Harwell, UK. EDS compositional data has been collected using the E01 microscope, whilst HRTEM and HAADF imaging data has been collected at E02. At E02 we are also applying a new 4D-STEM nano-diffraction technique in order to collect lattice spacing data to correlate with our other HRTEM results. Fe-K XANES analyses on Winchcombe and Ryugu have been carried out using the I18 microprobe and I14 hard x-ray nanoprobe respectively, also at Diamond Light Source, to constrain Fe3+/ΣFe. By combining these techniques we aim to better understand the physical and chemical structure of serpentine-like minerals in carbonaceous chondrites.
Initial analyses have shown that sulfur presence in carbonaceous chondrite phyllosilicates reduces the basal lattice spacings of serpentine-like minerals. In these sulfur-bearing regions, we have been finding lattice spacings in the range ~0.60-0.74nm for the CM-type chondrites. For the CI-type, these range between ~0.65-0.76nm. Differences in the reduced lattice spacing ranges are likely related to the redox state of the sulfur. In Ryugu and other carbonaceous chondrites the sulfur appears reduced; its content in serpentine is low and we see FeS grains. Comparatively, in Winchcombe (and others) more of the sulfur seems to be in the serpentine structure.
We can conclude that in serpentine-like minerals, the presence of sulfur appears to reduce basal lattice spacing values compared to the expected d-spacing value of 0.70nm for serpentine. Possible reasons for this include further investigations into the valency of the sulfur ions, the bonding environment within serpentine layers, and the location of sulfur in either the octa- or tetrahedral lattice sites.
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Feb 2023
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I14-Hard X-ray Nanoprobe
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Takaaki
Noguchi
,
Toru
Matsumoto
,
Akira
Miyake
,
Yohei
Igami
,
Mitsutaka
Haruta
,
Hikaru
Saito
,
Satoshi
Hata
,
Yusuke
Seto
,
Masaaki
Miyahara
,
Naotaka
Tomioka
,
Hope A.
Ishii
,
John P.
Bradley
,
Kenta K.
Ohtaki
,
Elena
Dobrică
,
Hugues
Leroux
,
Corentin
Le Guillou
,
Damien
Jacob
,
Francisco
De La Peña
,
Sylvain
Laforet
,
Maya
Marinova
,
Falko
Langenhorst
,
Dennis
Harries
,
Pierre
Beck
,
Thi H. V.
Phan
,
Rolando
Rebois
,
Neyda M.
Abreu
,
Jennifer
Gray
,
Thomas
Zega
,
Pierre-M.
Zanetta
,
Michelle S.
Thompson
,
Rhonda
Stroud
,
Kate
Burgess
,
Brittany A.
Cymes
,
John C.
Bridges
,
Leon
Hicks
,
Martin R.
Lee
,
Luke
Daly
,
Phil A.
Bland
,
Michael E.
Zolensky
,
David R.
Frank
,
James
Martinez
,
Akira
Tsuchiyama
,
Masahiro
Yasutake
,
Junya
Matsuno
,
Shota
Okumura
,
Itaru
Mitsukawa
,
Kentaro
Uesugi
,
Masayuki
Uesugi
,
Akihisa
Takeuchi
,
Mingqi
Sun
,
Satomi
Enju
,
Aki
Takigawa
,
Tatsuhiro
Michikami
,
Tomoki
Nakamura
,
Megumi
Matsumoto
,
Yusuke
Nakauchi
,
Masanao
Abe
,
Masahiko
Arakawa
,
Atsushi
Fujii
,
Masahiko
Hayakawa
,
Naru
Hirata
,
Naoyuki
Hirata
,
Rie
Honda
,
Chikatoshi
Honda
,
Satoshi
Hosoda
,
Yu-Ichi
Iijima
,
Hitoshi
Ikeda
,
Masateru
Ishiguro
,
Yoshiaki
Ishihara
,
Takahiro
Iwata
,
Kousuke
Kawahara
,
Shota
Kikuchi
,
Kohei
Kitazato
,
Koji
Matsumoto
,
Moe
Matsuoka
,
Yuya
Mimasu
,
Akira
Miura
,
Tomokatsu
Morota
,
Satoru
Nakazawa
,
Noriyuki
Namiki
,
Hirotomo
Noda
,
Rina
Noguchi
,
Naoko
Ogawa
,
Kazunori
Ogawa
,
Tatsuaki
Okada
,
Chisato
Okamoto
,
Go
Ono
,
Masanobu
Ozaki
,
Takanao
Saiki
,
Naoya
Sakatani
,
Hirotaka
Sawada
,
Hiroki
Senshu
,
Yuri
Shimaki
,
Kei
Shirai
,
Seiji
Sugita
,
Yuto
Takei
,
Hiroshi
Takeuchi
,
Satoshi
Tanaka
,
Eri
Tatsumi
,
Fuyuto
Terui
,
Ryudo
Tsukizaki
,
Koji
Wada
,
Manabu
Yamada
,
Tetsuya
Yamada
,
Yukio
Yamamoto
,
Hajime
Yano
,
Yasuhiro
Yokota
,
Keisuke
Yoshihara
,
Makoto
Yoshikawa
,
Kent
Yoshikawa
,
Ryohta
Fukai
,
Shizuho
Furuya
,
Kentaro
Hatakeda
,
Tasuku
Hayashi
,
Yuya
Hitomi
,
Kazuya
Kumagai
,
Akiko
Miyazaki
,
Aiko
Nakato
,
Masahiro
Nishimura
,
Hiromichi
Soejima
,
Ayako I.
Suzuki
,
Tomohiro
Usui
,
Toru
Yada
,
Daiki
Yamamoto
,
Kasumi
Yogata
,
Miwa
Yoshitake
,
Harold C.
Connolly
,
Dante S.
Lauretta
,
Hisayoshi
Yurimoto
,
Kazuhide
Nagashima
,
Noriyuki
Kawasaki
,
Naoya
Sakamoto
,
Ryuji
Okazaki
,
Hikaru
Yabuta
,
Hiroshi
Naraoka
,
Kanako
Sakamoto
,
Shogo
Tachibana
,
Sei-Ichiro
Watanabe
,
Yuichi
Tsuda
Open Access
Abstract: Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.
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Dec 2022
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I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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Abstract: New mineralogical studies of Lafayette reveal that it contains a notably variable abundance of martian carbonate. Four percent was identified in mesostasis (3.2%) and olivine-hosted (0.8%) fractures in one polished section, but only 0.2% of both textural types in another. The Lafayette carbonates are Mg0.0-2.0Cc13.2-38.6Sd17.7-81.9Rh3.1-42.9. They have undergone variable but extensive amounts of dissolution and replacement as the nakhlite secondary fluid evolved, associated with the precipitation of ferric saponite in olivine fractures and a serpentine-like phyllosilicate in the mesostasis. The mesostasis carbonate has undergone the highest degree of corrosion and replacement. TEM analysis has shown the presence of Fe-(hydr)oxide (likely ferrihydrite) nanoparticles on olivine-hosted carbonates which can be linked to the cessation of more extensive carbonate dissolution at those sites. The mesostasis serpentine-like mineral has been described here on the basis of WDS and EDX analyses, HRTEM and Fe-K XANES, as odinite, a ferric, 0.7 nm d001-spacings phyllosilicate mineral with a characteristic 1:1 serpentine-like structure. The carbonate dissolution stage and then formation of Fe-(hydr)oxide nanoparticles occurred under circumneutral-alkaline conditions 7 < pH < 10. This range of pH is also where the general dissolution mechanism switched from a proton-promoted, to a water hydrolysis reaction associated with a reduction in the dissolution rates. As dissolution rates were reduced and the fluid had cooled to ≤50°C, the precipitation of the ferric saponite and odinite, a phyllosilicate associated with temperatures of ∼25°C, dominated over the carbonate dissolution. The extensive dissolution of such crustal carbonate across the upper martian crust, producing bicarbonate and carbon dioxide, and the coupled formation of ferric phyllosilicates, would lead to the formation of CH4 in substantial amounts via a Fischer-Tropsch type reaction. The results of our study illustrate a process to explain the relatively low abundance of detected carbonate on Mars and a likely source for some of the methane on Mars.
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Feb 2022
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Abstract: Introduction: Airless planetary bodies with surfaces exposed to the space environment are bombarded by electrons and protons from the solar wind and cosmic rays, as well as micrometeorites, resulting in space weathering [1]. Features of space weathering include partially amorphised grain surface rims, measuring up to
~100 nm thick, containing nanophase Fe metal (npFe0) particles, vesicular blistering, and solar flare tracks [1,2].
Space weathered samples collected by the JAXA Hayabusa spacecraft from asteroid Itokawa have previously been analysed using the I14 X-ray nanoprobe beamline at Diamond Light Source synchrotron, measuring Fe-K
X-ray absorption near-edge spectroscopy (XANES), and revealing an increased ferric-ferrous ratio (Fe3+/ΣFe) relative to their respective host grain mineralogy [3].
In this study, we seek to better understand the formation of space weathered lunar surface soil samples collected during the Apollo 17 mission, investigating the Fe-redox variations observed in the dominant silicate phase and the nano-grains of the space weathered rims using Fe-K XANES and EELS, with high-resolution STEM imaging.
Methods/Materials: The lunar sample number is 78481,29 - a surface sample collected from the top 1 cm of trench soils at Station 8 of Apollo 17 [4]. Three FIB lift-out sections have been extracted successfully from lunar grains identified to have space weathered surfaces. Two of the lunar grains were augite pyroxene, En81Fs16 and En85Fs12, and one olivine, Fa39.
Using the I14 X-ray Nanoprobe Beamline at Diamond, Fe-Kα XAS spectra are obtained from a series of XRF maps over the samples, with energies typically in the range 7000-7300 eV, with a higher energy resolution range over the XANES features (~7100-7150 eV). The XANES maps are processed using Mantis 2.3.02 [5], and isolated spectra normalized in Athena 0.8.056 [6]. By observing increasing shifts in the 1s→3d transition pre- absorption-edge peak centroid energy positions, the Fe-redox variations can be estimated between the sample host mineralogy and the space weathered zone, when compared to reference minerals of known ferric-ferrous
ratio (Fe3+/ΣFe).
A JEOL ARM200CF and JEOL JEM-ARM300CF instrument was used for EELS analyses and high-resolution STEM imaging respectively, at ePSIC in Diamond. EELS are performed using an accelerating voltage of 200 keV, current 15 μA, and 0.25eV/ch with a 5 mm EELS aperture, measuring linescans from the host to the space weathered zones to provide verification of the Fe-redox variation by observing the shifts in the Fe-Lα peaks.
Results: HR-STEM imaging confirmed the expected partial amorphisation and npFe0 particles (Fe0 metal confirmed observing lattice fringe spacings of ~2.06 Å) in the space weathered zones of all three lunar samples.
XANES mapping was able to identify the space weathered zone separate from the host grain mineralogy, and analyses of the XANES spectra from each revealed a consistent positive shift in the 1s→3d pre-edge centroid energy positions for the space weathered zone when compared to the host. Increases of up to ~0.23 eV in the space weathered (SW) zone, compared to the substrate host mineralogy of augite or olivine, suggests an
increase in ferric content in the space weathered zones up to ΔFe3+/ΣFe ~0.14 ±0.03. Positive shifts in the absorption edge positions for SW zones also support these results.
A total of 18 EELS linescans measured, at various locations along the space weathered rims in all three lunar samples, also shows a consistent increased shift in the Fe-L peak energy position. A positive shift in the EELS Fe-L peak position is indicative of increased ferric content, as shown by reference minerals measured including
Fe-rich olivine (Fe3+/ΣFe = 0.00) and magnetite (Fe3+/ΣFe = 0.67) with average EELS Fe-L peak positions of ~712.1 eV and ~713.6 eV respectively.
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Jul 2021
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[19641, 23232, 26303]
Open Access
Abstract: Synchrotron Fe‐K X‐ray absorption spectroscopy and transmission electron microscopy have been used to investigate the mineralogy and Fe‐redox variations in the space‐weathered (SW) rims of asteroidal samples. This study focuses on the FIB lift‐out sections from five Itokawa grains, returned by the Hayabusa spacecraft, including samples RB‐QD04‐0063, RB‐QD04‐0080, RB‐CV‐0011, RB‐CV‐0089, and RB‐CV‐0148. Each of the samples featured partially amorphized SW rims, caused by irradiation damage from implanted low mass solar wind ions, and the impacting of micrometeorites. Using bright‐field and HAADF‐STEM imaging, vesicular blistering and nanophase Fe metal (npFe0) particles were observed within grain rims, and solar flare tracks were observed in the substrate host grain, confirming the presence of SW zones. We use Fe‐K XANES mapping to investigate Fe‐redox changes between the host mineral and the SW zones. All SW zones measured show some increases in the ferric‐ferrous ratio (Fe3+/ΣFe) relative to their respective host grains, likely the result of the implanted solar wind H+ ions reacting with the segregated ferrous Fe in the surface material.
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Jan 2021
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Open Access
Abstract: Space weathering due to the bombardment of electrons and solar wind upon the exposed lunar surface shows as an apparent spectral darkening and reddening in ground-based and lunar-orbital observations. Space weathered rims have been observed on soil surface samples, returned by the Apollo landings, featuring amorphized material and nanophase Fe metal (npFe⁰) particles formed due to the implantation of solar wind H⁺ ions reducing the host grain mineral oxides to form metal. Oxidation of these Fe particles has also been shown, and a suggested correlation between oxidation and lunar soil maturity.In this study, we investigate Fe-redox changes in the space weathered rims of Apollo 17 lunar surface soil samples, using TEM and X-ray nanoprobe Fe-K XANES.
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Sep 2020
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I18-Microfocus Spectroscopy
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Abstract: We report on the alteration history of the olivine-phyric, highly depleted (HD) shergottite, Northwest Africa (NWA) 10416, paying particular attention to the origin of the aqueous alteration seen affecting the meteorite’s olivine megacrysts. The rock’s interior displays 1 mm, zoned, altered olivine megacrysts set in a groundmass of clinopyroxene, unzoned olivine, and interstitial plagioclase and maskelynite. Synchrotron micro X-ray diffraction (µ-XRD) and transmission electron microscopy (TEM) show that plagioclase and maskelynite have been partially replaced by kaolinite. The relict olivine megacryst cores display a unique concentric colouration for Martian meteorites, having central amber-coloured zones surrounded by a brown mantle zone, with the rims remaining clear and unaltered. This colouration is a result of fluid alteration and partial replacement, with hydration. TEM analysis revealed the ∼200 nm scale banded and largely amorphous nature of the alteration, but with some (∼ 20%) relict crystalline olivine patches. Although the coloured olivine zones show cation and anion site vacancies compared to stoichiometric olivine, a relict igneous compositional trend is preserved in the megacrysts, from Mg-rich altered cores (Mg# = 76) to unaltered stoichiometric rims (Fo53). Synchrotron Fe-K X-ray absorption near-edge structure (XANES) analysis revealed that the coloured zones of the megacryst have different Fe oxidation values. High ferric contents are present in the brown mantle zones (Fe3+/ΣFe ≤ 0.92) and the amber zones (Fe3+/ΣFe ≤ 0.30), whereas the clear rims are ferrous. This suggests alteration occurred in an oxidising environment and that the sharp contrast in colour of the megacryst (brown to clear) is a record of a relict fluid reaction front.
In order to test the terrestrial or extraterrestrial origin of the alteration, olivine material from a shock-melt vein was analysed by TEM. The analysis revealed 0.952 nm curved d-spacing’s from clay alteration undisturbed by any shock effects, strongly suggesting a terrestrial origin. The d-spacing values most likely represent a collapsed saponite or vermiculite, showing that in some places olivine has been replaced by crystalline clay.
Oxygen isotope analysis of bulk (Δ17O = 0.309 ± 0.009 (2σ) ‰) and amber-coloured megacryst material (= 0.271 ± 0.002 (2σ) ‰), are also consistent with terrestrial alteration. We propose a model in which, during the meteorite’s time in Northwest Africa, low-temperature, likely acidic, groundwater exploited fractures. The fluid altered the olivine megacrysts in a way that was controlled by the pre-existing, igneous compositional zonation, with Mg-rich olivine being more susceptible to alteration in this fluid environment. The plagioclase and maskelynite were also altered to a high degree. After the alteration event it is likely that NWA 10416 had a significant residence time in Northwest Africa, accounting for terrestrial calcite and the dehydration of some clay phases.
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Apr 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
I18-Microfocus Spectroscopy
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J. L.
Macarthur
,
J. C.
Bridges
,
L. J.
Hicks
,
R.
Burgess
,
K. H.
Joy
,
M. J.
Branney
,
G. M.
Hansford
,
S. H.
Baker
,
S. P.
Schwenzer
,
S. J.
Gurman
,
N. R.
Stephen
,
E. D.
Steer
,
J. D.
Piercy
,
T. R.
Ireland
Diamond Proposal Number(s):
[10328, 12761, 13690, 16688, 19641]
Abstract: Martian meteorite Northwest Africa (NWA) 8114 – a paired stone to NWA 7034 – provides an opportunity to examine the thermal history of a martian regolith and study near-surface processes and ancient environmental conditions near an impact crater on Mars. Our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains. Some of the pyroxene clasts show exsolution lamellae, indicating a high temperature magmatic origin and slow cooling. However, transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re-crystallised to form magnetite and a K-bearing feldspathic glassy material, together with relict pyroxene. This breakdown event was associated with oxidation, with up to 25% Fe3+/ΣFe in the relict pyroxene measured using Fe-K XANES. By comparison with previous studies, this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating, being held at a temperature above 700 °C for at least 7 days in an oxidising regolith environment.
We report an approximate 40Ar-39Ar maximum age of 1.13 Ga to 1.25 Ga for an individual, separated, augite clast. The disturbed nature of the spectra precludes precise age determination. In section, this clast is porous and contains iron oxide grains. This shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts, and has up to 25% Fe3+/ΣFe. We infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes, after consolidation of the impact ejecta blanket.
High temperatures, above 700 °C, may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut, and in some cases surround, the oxidised pyroxene. However, the veins could alternatively be the result of a hydrothermal event in the impact regolith. A simple Fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days.
Low temperature hydrous alteration took place forming goethite, identified via XRD, XANES and FTIR. Comparing with previous studies, the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite.
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Nov 2018
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1833, 7487, 9418, 10328, 13690]
Open Access
Abstract: The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s−1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.
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Jul 2017
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