E01-JEM ARM 200CF
E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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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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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
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J. C.
Bridges
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L. J.
Hicks
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R.
Burgess
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K. H.
Joy
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M. J.
Branney
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G. M.
Hansford
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S. H.
Baker
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S. P.
Schwenzer
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S. J.
Gurman
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N. R.
Stephen
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E. D.
Steer
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J. D.
Piercy
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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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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[13690]
Open Access
Abstract: Using the data we have gathered at I18 on micron-size grains returned by Stardust from Comet Wild2, we hypothesise that this comet has affinities to CO and CR carbonaceous chondrites. For instance, the abundance of magnetite (Fe3O4) grains that we identified in previous I18 experiments [1] demonstrates the action of liquid water on the parent body. By analysing CR chondrite powder shot into aerogel at 6 kms-1, and also newly harvested Wild2 aerogel tracks we made accurate comparisons between chondrites and the comet. This demonstrates that the mineral assemblages preserved in the Stardust tracks were formed from carbonaceous chondrite like material. We also conducted a pilot XRD, XANES study on newly discovered martian meteorites also analyse recently discovered martian meteorites in order to characterise the mineralogical effects of water-rock reaction. We will complete the latter study in a future planned experiment.
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Jul 2016
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B22-Multimode InfraRed imaging And Microspectroscopy
I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[12761]
Open Access
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Mar 2016
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[9418, 10328]
Open Access
Abstract: NWA 8114 (a pair of NWA 7034) is
a polymict [1] martian basaltic breccia [2] with a bulkrock
age of ~2.1 Ga [2] containing zircons dated at
~4.4 Ga [3]. It is the first sample of the martian regolith
[3], with varied clasts bound in a fine grained matrix
[4].
As the most hydrated martian meteorite identified
to date [2], the majority of the water is thought to be
hosted by hydrous Fe oxides, with a minor contribution
from apatite [5]. The ferric phrases maghemite and
goethite have been detected [6], making this potentially
the most oxidized known martian meteorite [1,6]. The
oxygen isotope ratio of water shows Δ17O values above
the terrestrial fractionation line and the D/H isotope
ratio analyses also support the martian origin of water
in NWA 7034 [2].
The meteorite was likely formed as a result of an
impact event [7] which may have led to hydrothermal
systems causing further alteration to it [6,8]. Our work
characterises the partial breakdown, and mantling by
fine-grained material, of pyroxene clasts, in terms of
their oxidation state and related textures. We combine
this with mineral thermometry to reveal the thermal
history of the impact regolith within which the parent
rock of this meteorite formed.
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Feb 2015
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[9418, 10328]
Open Access
Abstract: We present Raman spectroscopy results
from a set of terminal grains found in tracks
C2112,4,187,0,0 (187, 9 grains), C2045,2,188,0,0
(188, 4 grains), C2045,3,189,0,0 (189, 3 grains) and
C2045,4,190,0,0 (190, 3 grains) taken from the cometary
side of NASAs Stardust mission sample collector
[1]. In order to maximise the scientific return, it is
vital that analyses of the samples are undertaken using
as many different, non-destructive, techniques as possible
- preferably on particles whilst they are still embedded
in aerogel using
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Feb 2015
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[6372, 7487, 8307, 9418, 10328]
Open Access
Abstract: The work described in this thesis features the study of planetary materials, including nakhlite martian meteorites, comet 81P/Wild2 grains, and asteroid Itokawa 25143 particles, using various electron microscopy techniques and X-ray spectroscopy.
Transmission electron microscopy (TEM), Fe-K X-ray absorption spectroscopy (XAS) and in-situ Transmission X-ray Diffraction (XRD) have been used to determine the structure, ferric content and stoichiometry in the secondary phase mineral assemblages of the nakhlites. By measuring the energy position of the Fe-K XANES 1s→3d pre-edge transition centroid, the Fe3+-rich nature of these minerals has been shown. Analyses of the crystalline phyllosilicates in Lafayette found trioctahedral ferric saponite with a 2:1 T-O-T lattice structure and d001-spacings of 0.96 nm, as well as Fe-serpentine with a 1:1 T-O structure and d001-spacings of 0.7 nm. A ferric poorly crystalline or amorphous gel of similar composition to the phyllosilicates was found as fracture fills throughout the other nakhlites.
XRD and Fe-K XAS also allow the mineralogical identification of comet Wild2 terminal grains. The terminal grains of Tracks #170 and #176 are Fe-metal, with hematite subgrain material in #170. The terminal grain of #170 also includes Cr-bearing silicate, similar to the Cr-bearing terminal grain of Track #177. Olivine was found amongst the terminal grains of Track #178 alongside magnetites. The presence of magnetite is consistent with low temperature water-rock interaction similar to a carbonaceous chondrite matrix.
XAS has also been used to study Itokawa particles, finding ferrous olivines and pyroxenes, as well as studying other metals and Ni-bearing phases. Comparisons with the Tuxtuac meteorite showed the similarity of Itokawa particles to that of LL5 and LL6 chondrite materials.
Measuring Fe-K XAS and XRD has proved to be an effective and non-destructive method for mineralogical characterisation of planetary samples, and determining the oxidation state of Fe-silicates, especially on a micron scale. These will be essential techniques for future sample return missions and meteorite finds.
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Jan 2015
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