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Abstract: This thesis focuses on the mineralogical study of altered martian meteorites and the development of a novel wet-chemistry instrument. X-ray spectroscopy and electron microscopy have been used to investigate the secondary mineralogy of martian meteorites and their associated fluids. Martian analogue brines were investigated with transmission spectroscopy in order to address the technique’s capabilities for detecting dilute, astrobiologically significant fluids. The newly-found martian shergottite, Northwest Africa (NWA) 10416, bears a distinctive colouration in its olivine megacrysts which is suggestive of hydrous alteration. The meteorite has been petrographically characterised and the origin of its alteration has been determined as terrestrial. Oxygen isotope analysis and the observation of secondary phases within shock features using Transmission Electron Microscopy (TEM) have indicated a terrestrial fluid. Synchrotron X-ray Absorption Spectroscopy (XAS), X-ray Diffraction (XRD) and Electron Probe Micro-Analysis (EPMA) have allowed its characterisation as a low-temperature, possibly acidic, fluid. Analysis of the martian nakhlite, Lafayette, has been performed in order to assess the extent of carbonate dissolution by a hydrothermal martian fluid. Textures determined by Scanning Electron Microscopy (SEM) and TEM, and compositions determined by EPMA and XAS have displayed the variable nature of this dissolution and allowed the identification of the mesostasis phyllosilicate as odinite. This work has illustrated a process in which martian crustal fluids can dissolve carbonates and produce substantial amounts of methane, informing our understanding of martian atmospheric methane. The capabilities of transmission spectroscopy when detecting organic martian analogue brines have been assessed to further the development of the wet-chemistry instrument, ASPIRE. Transmission spectroscopy was unsuccessful in detecting the likely low organic concentrations (ppb) expected in potentially habitable martian aqueous environments. However, future avenues of research have been suggested for consideration, including investigation into the potential of reflectance spectroscopy and calibration of ASPIRE to mineralogical-free regions within the infrared region.

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Abstract: Jarosite is a common mineral on the surface of Mars, but relatively rare on Earth. Since the Opportunity rover reported widespread jarosite at Meridiani Planum in 2004, the mineral has been repeatedly identified on Mars. On Earth, jarosite forms through the weathering of iron-bearing minerals in water-limited settings. However, scientists have struggled to understand how the mineral may have formed on Mars. An international group of researchers have therefore studied whether glaciers played a role in the precipitation of jarosite on Mars in its geologic past. The ‘ice-weathering model’ suggests that the precipitation of jarosite on Mars could be related to the presence of massive ice deposits developed during ancient glacial ages. To test this hypothesis, the researchers investigated the properties of deep Antarctic ice, as an Earth analogue for paleo-ice deposits on Mars. Diamond Light Source’s B18 beamline is dedicated to X-ray Absorption Spectroscopy. This technique can characterise geochemical and mineralogical properties, even on tiny mineral dust samples extracted from Antarctic ice. The team measured more than 50 samples retrieved from the Antarctic Talos Dome ice core. They observed jarosite present in deep ice and depicted a coherent scenario to describe the formation of this mineral. Their scenario is consistent with the ice-weathering model, supporting the hypothesis that glaciers had a fundamental role in shaping the geologic and geochemical past of Mars.

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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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Abstract: The CM carbonaceous chondrite meteorites provide a record of low temperature (<150 °C) aqueous reactions in the early solar system. A number of CM chondrites also experienced short-lived, post-hydration thermal metamorphism at temperatures of ∼200 °C to >750 °C. The exact conditions of thermal metamorphism and the relationship between the unheated and heated CM chondrites are not well constrained but are crucial to understanding the formation and evolution of hydrous asteroids. Here we have used position-sensitive-detector X-ray diffraction (PSD-XRD), thermogravimetric analysis (TGA) and transmission infrared (IR) spectroscopy to characterise the mineralogy and water contents of 14 heated CM and ungrouped carbonaceous chondrites. We show that heated CM chondrites underwent the same degree of aqueous alteration as the unheated CMs, however upon thermal metamorphism their mineralogy initially (300–500 °C) changed from hydrated phyllosilicates to a dehydrated amorphous phyllosilicate phase. At higher temperatures (>500 °C) we observe recrystallisation of olivine and Fe-sulphides and the formation of metal. Thermal metamorphism also caused the water contents of heated CM chondrites to decrease from ∼13 wt% to ∼3 wt% and a subsequent reduction in the intensity of the 3 μm feature in IR spectra. We estimate that the heated CM chondrites have lost ∼15 - >65% of the water they contained at the end of aqueous alteration. If impacts were the main cause of metamorphism, this is consistent with shock pressures of ∼20–50 GPa. However, not all heated CM chondrites retain shock features suggesting that some were instead heated by solar radiation. Evidence from the Hayabusa2 and ORSIRS-REx missions suggest that dehydrated materials may be common on the surfaces of primitive asteroids and our results will support upcoming analysis of samples returned from asteroids Ryugu and Bennu.

Open Access

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Abstract: Many interpretations have been proposed to explain the presence of jarosite within Martian surficial sediments, including the possibility that it precipitated within paleo-ice deposits owing to englacial weathering of dust. However, until now a similar geochemical process was not observed on Earth nor in other planetary settings. We report a multi-analytical indication of jarosite formation within deep ice. Below 1000 m depth, jarosite crystals adhering on residual silica-rich particles have been identified in the Talos Dome ice core (East Antarctica) and interpreted as products of weathering involving aeolian dust and acidic atmospheric aerosols. The progressive increase of ice metamorphism and re-crystallization with depth, favours the relocation and concentration of dust and the formation of acidic brines in isolated environments, allowing chemical reactions and mineral neo-formation to occur. This is the first described englacial diagenetic mechanism occurring in deep Antarctic ice and supports the ice-weathering model for jarosite formation on Mars, highlighting the geologic importance of paleo ice-related processes on this planet. Additional implications concern the preservation of dust-related signals in deep ice cores with respect to paleoclimatic reconstructions and the englacial history of meteorites from Antarctic blue ice fields.