Roberta Flemming

Roberta Flemming
Western University | UWO · Department of Earth Sciences

Professor

About

145
Publications
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Publications

Publications (145)
Article
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Spinel-group minerals are among the best-known and widely used minerals in diamond exploration due to their ubiquity, resistance to weathering, and utility as petrogenetic indicators. The kimberlite indicator mineral chromite is investigated in this study using micro-X-ray diffraction (µXRD) to measure chromite unit cell parameter ao. We used epoxy...
Article
Electron backscatter diffraction (EBSD) investigation of strain mainly uses polycrystalline samples to study fabric development. We extend the use of EBSD for the analysis of large single mineral grains by measuring the apparent surficial subdomain boundary density per unit area, reported here as unit segment length (USL). We apply this USL techniq...
Article
Minerals extracted from two calcium-aluminum-rich inclusions, one each from NWA 2364 and NWA 6991 CV3 chondrite meteorites, were examined using micro X-ray diffraction, 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and Triple Quantum (3Q) MAS NMR. In situ examination by micro X-ray diffraction was used to confirm the p...
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The ~5 km diameter Gow Lake impact structure formed in the Canadian Shield of northern Saskatchewan approximately 197 Myr ago. This structure has not been studied in detail since its discovery during a regional gravity survey in the early 1970s. We report here on field observations from a 2011 expedition that, when combined with subsequent laborato...
Article
Ureilites are the second most abundant achondrite meteorite group, yet they are from an unknown source. They are ultramafic in composition and have undergone thermal metamorphism as well as shock deformation since their formation. In this work, olivine grains from six monomict ureilites, Northwest Africa 7059, Elephant Moraine 96042, Shişr 007 (all...
Article
The impact melt‐bearing breccias at the Ries impact structure, Germany, host degassing pipes: vertical structures that are inferred to represent conduits along which gases and fluids escaped to the surface, consistent with hydrothermal activity that occurs soon after an impact event. Although the presence of degassing pipes has been recognized with...
Article
Lunar impact melt deposits have unusual surface properties, unlike any measured terrestrial lava flow. Radar observations suggest that they are incredibly rough at decimeter scales, but they appear smooth in high-resolution, meter-scale optical images. The cause of their unusual surface roughness is unknown. In this work, we investigate the propert...
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Ordinary chondrites record shock metamorphism resulting from hypervelocity collisions on small bodies, and underpin the petrographic assessment of shock stage, a scale of progressive stages of shock metamorphism from S1 (unshocked) to S7 (shock melted). In this work, olivine grains in 11 L and LL chondrites (S1–S5) were investigated in thin section...
Article
Large mineral grains that have undergone shock metamorphism or tectonic stress can exhibit plastic deformation. Using in situ micro X-Ray diffraction, such deformation is revealed in a 2D detector image by distortion of diffraction spots into an angular spread or ‘streaking’ along Debye ring or chi (χ) dimension; this can provide a quantitative mea...
Article
Niobium and tantalum, rare metals and high field strength elements (HFSEs) that are essential to modern technologies, are concentrated among others in lithium-cesium-tantalum (LCT) pegmatites and rare metal granites. The most important hosts for Nb-Ta in these types of deposits are the columbite group minerals (columbite-tantalite), but at some ore...
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Exploration of microbial-meteorite redox interactions highlights the possibility of bioprocessing of extraterrestrial metal resources and reveals specific microbial fingerprints left on extraterrestrial material. In the present study, we provide our observations on a microbial-meteorite nanoscale interface of the metal respiring thermoacidophile Me...
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Volcanic glasses are rarely preserved in the rock record, and the quality of preservation generally declines with increasing age. Records preserved in ancient basaltic glasses therefore provide important links between processes operating in the distant past, and those that are active on the Earth today. Microbial colonization has been linked to the...
Article
Ore minerals of niobium and tantalum are typically associated with pegmatites and rare metal granites; these include columbite, tantalite, wodginite, titanowodginite, microlite and pyrochlore. Solubility and crystallization mechanisms for columbite-(Mn) and tantalite-(Mn) have been extensively studied in haplogranitic melts, with little research in...
Article
Background: X-ray computed tomography (CT) can non-destructively examine objects by producing three-dimensional images of their internal structure. Although the availability of biomedical micro-CT offers the increased access to scanners, CT images of dense objects are susceptible to artifacts particularly due to beam hardening. Objective: This s...
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Hollow tubular structures in subaqueously-emplaced basaltic glass may represent trace fossils caused by microbially-mediated glass dissolution. Mineralized structures of similar morphology and spatial distribution in ancient, metamorphosed basaltic rocks have widely been interpreted as ichnofossils, possibly dating to ∼3.5 Ga or greater. Doubts hav...
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All Martian meteorites have experienced shock metamorphism to some degree. We quantitatively determined shock‐related strain in olivine crystals to measure shock level and peak shock pressure experienced by five Martian meteorites. Two independent methods employing nondestructive in situ micro X‐ray diffraction (μXRD) are applied, i.e., (1) the lat...
Article
Exploration for mineral deposits is becoming increasingly difficult, requiring the use of novel approaches that are reliable and cost-effective. One such approach is the use of vein-hosted mineral chemistry. A number of studies have described the use of vein-hosted mineral chemistry as an exploration tool, but few have assessed a variety of factors...
Conference Paper
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Introduction: Observation of shock metamorphism in rocks is the primary method of determining if they have been exposed to a hypervelocity impact. This is necessary to confirm any proposed new impact structure [1]. Shatter cones are the only macroscopic evidence of shock and they may not be generated in all rock types or even preserved in every cra...
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Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples were analyzed for Ag mineralogy, content, and distribution using mi...
Article
Knowing the amount and timing of water incorporation into the Moon has fundamental implications for our understanding of how the Earth–Moon system formed. Water has been detected in lunar samples but its abundance, distribution and origin are debated. To address these issues, we report water concentrations and hydrogen isotope ratios obtained by se...
Article
Zinc and germanium enrichments have been discovered in sedimentary rocks in Gale Crater, Mars, by the Alpha Particle X-ray Spectrometer (APXS) on the rover Curiosity. Concentrations of Zn (910 ± 840 ppm) and Ge (65 ± 58 ppm) are 10s-100s of times greater than in Martian meteorites and estimates for average silicate Mars. Enrichments occur in divers...
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We describe occurrences of palladoan melonite in intimate intergrowths with cobaltite-gersdorffite from the Neoproterozoic dunite-wehrlite-gabbro complexes of Kingash and Kuskanak, Eastern Sayans, Russia. The observed compositional trends of melonite are consistent with the overall variations examined on the basis of numerous literature sources. Th...
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The geochemistry and bulk mineralogy of surface (0-30 cm) and subsurface (60-90 cm) soil samples in the bitumen environment of Ondo State Nigeria was studied using X-Ray Florescence and X-Ray Diffraction techniques. The bulk minerals were qualitatively studied with EVA software and quantified using Rietveld refinement method. The mineralogy was fou...
Article
Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite-bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in...
Article
The ~15 Ma, 26 km diameter Ries impact structure in south-central Germany was one of the first terrestrial impact structures where evidence of impact-associated hydrothermal alteration was recognized. Previous studies suggested that pervasive, high-temperature hydrothermal activity was restricted to the area within the “inner ring” (i.e., the crate...
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The presence of potential microbial trace fossils (endolithic microborings) has been well documented in oceanic basaltic pillow lavas, hyaloclastites, tuffs, and transitional subglacial marine lavas in the past 30 yr. Despite their evident abundance in oceanic to subglacial environments, they have not been observed in continental basalts that were...
Article
We investigate an outcrop of ∼187 Ma lacustrine pillow basalts of the Talcott Formation exposed in Meriden, Connecticut, USA, focusing on coordinated analyses of one pillow lava to characterize the aqueous history of these basalts in the Hartford Basin. This work uses a suite of multidisciplinary measurements, including hyperspectral imaging, other...
Conference Paper
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Can magmatic olivine deform in the magma plumbing system of volcanoes (and how)? This issue is still a matter of debate, and although vastly documented for mantle rocks, plastic deformation of magmatic olivine in volcanic rocks – xenolith nodules not considered – lacks constraints. Here, we address the question and provide new insights through a co...
Article
27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) and 27Al triple quantum (3Q) MAS NMR spectroscopy have been performed at 21.1 Tesla (T), as a direct probe of environment around Al in synthetic Ca-Tschermak's clinopyroxene, CaAlAlSiO6, henceforward referred to as CaTs. For comparison, 27Al MAS NMR of CaTs has also been performed at 14...
Article
Studies of shock metamorphism of feldspar typically rely on qualitative petrographic observations, which, while providing invaluable information, can be difficult to interpret. Shocked feldspars, therefore, are now being studied in greater detail by various groups using a variety of modern techniques. We apply in situ micro-X-ray diffraction (μXRD)...
Conference Paper
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Can plastic deformation occur at crustal levels and form strained olivine in volcanic rocks? This is matter of debate and currently poorly constrained, although deformed olivine is abundant in volcanic rocks from various geodynamic settings. Magmatic deformation of olivine has been mostly ignored in favour of an upper mantle origin, but the petrolo...
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Shock metamorphism, caused by hypervelocity impact, is a poorly understood process in feldspar due to the complexity of the crystal structure, the relative ease of weathering, and chemical variations, making optical studies of shocked feldspars challenging. Understanding shock metamorphism in feldspars, and plagioclase in particular, is vital for u...
Article
Two-dimensional X-ray diffraction data contain information about not only the type of mineral phases present in an assemblage, but also the textural or grain size relationships between minerals in a sample. For minerals within a certain grain size range, ∼0.1 to 100 μm, the appearance and characteristics of a Debye ring can reveal the mean grain si...
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The putative occurrence of methane in the Martian atmosphere has had a major influence on the exploration of Mars, especially by the implication of active biology. The occurrence has not been borne out by measurements of atmosphere by the MSL rover Curiosity but, as on Earth, methane on Mars is most likely in the subsurface of the crust. Serpentini...
Conference Paper
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Spectral mapping of a calcite-marcasite vug and its weathering products shows evolution from hot, reducing to cooler, oxidizing to chemically complex fluids.
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Mineralogical data from surficial suevite sampled at depth from Ries suggest impact-induced hydrothermal activity occurred beyond the crater rim.
Conference Paper
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Micro-CT scanning of Zaklodzie and NWA4301 meteorites show differences in silicate intensity, metal distribution, shape, and connectivity from 3-D image rendering.
Article
Modern Martian dust is similar in composition to the global soil unit and bulk basaltic Mars crust, but it is enriched in S and Cl. The Alpha Particle X-ray Spectrometer (APXS) on the Mars Science Laboratory Curiosity rover analyzed air fall dust on the science observation tray (o-tray) in Gale Crater to determine dust oxide compositions. The o-tra...
Article
Precipitation of calcium carbonate (CaCO3(s)) can be driven by microbial activity. Here, a systematic approach is used to identify the morphological and mineralogical characteristics of CaCO3(s) precipitated during the heterotrophic growth of micro-organisms isolated from polar environments. Focus was placed on establishing mineralogical features t...
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A bstract Guyanaite, naturally occurring b-CrOOH, has been identified in a xenolith of Cr-rich omphacitite from the Moses Rock diatreme in the Navajo Volcanic Field of the southwestern United States. It occurs as the dominant phase in small clusters of accessory minerals, intergrown with kosmochlor-rich omphacite, zincian chromite, eskolaite, and c...
Article
A temperature-controlled sample stage with an operational range of ~60 °C above or below ambient laboratory temperature (~ −35 to 85 °C) was constructed for in situ X-ray diffraction of minerals and materials using a Bruker D8 Discover diffractometer with θ-θ geometry. The stage was primarily designed for characterizing mirabilite-bearing samples f...
Conference Paper
A 2-D XRD grain size estimation is performed on minerals of known sieve fraction grain sizes, and then applied to 2-D XRD data from the Mars Science Laboratory.
Conference Paper
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Biogenic calcium carbonate may be a biosignature of extinct life on Mars. We investigated the mineralogy and morphology of carbonate precipitated by microbes.
Article
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µXRD for the purpose of quantifying shock level is being applied for the first time to the feldspar group using both terrestrial impactites and Apollo samples.
Conference Paper
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Glasses produced by hypervelocity impact may be responsible for some spectral properties heretofore attributed to space weathering or acidic leaching processes.
Article
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Textural and mineralogical investigations of basaltic tuffs reveal a succession that lead to habitable conditions as evidenced by endolithic microbores.
Article
Laboratory medical CT imaging can provide relatively high resolution 3-D information on the distribution of density within meteorites.
Article
Recovery of phosphorus from wastewater as calcium phosphate could diminish the need for mining of scarce phosphate rock resources. This study introduces a novel approach to phosphorus recovery by precipitation of calcium phosphate granules in anaerobic treatment of black water. The granules formed in the Upflow Anaerobic Sludge Blanket (UASB) react...
Article
The SNC meteorites represent potentially habitable substrates for chemolithoautotrophs on Mars, but the conditions in the rocky subsurface will be site specific and much more limiting to microbiota than the inorganic mineral components of the crust.
Article
Non-destructive in situ micro XRD analyses were done of broken surface, shock vein and fusion crust locations for fragments from the Chelyabinsk fall. Crystal structural data shows an LL classification, moderate shock and odd phases in fusion crust.
Data
With the discovery of NWA 7034, which is classified as Mar-tian basaltic breccia, and recent geochemical data from NASA's missions [1 & refs. therein], questions arise as to what extent Shergottite-Nakhlite-Chassignite (SNC) meteorites represent the crustal diversity of Mars. Oxygen isotope signatures in SNCs can be used to constrain primary and se...
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Dioctahedral clays from an active continental geothermal system have been studied to assess their usefulness as proxies of paleo-hydrological and thermal conditions in the subsurface. Drill cuttings from Well WK244 in the Te Mihi area of the Wairakei Geothermal Field, New Zealand, were analyzed to determine the mineralogical, morphological, and iso...
Conference Paper
A temperature-controlled sample stage was created for a micro-X-ray diffractometer to analyse samples from an Arctic saline spring at an in situ temperature.
Article
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Textural features within coarse-grained basaltic pyroclasts suggest that vesicle micro-environments may be conducive to habitable conditions on Mars.
Conference Paper
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The XRD pattern of amorphous glasses can be used identify source/composition despite lack of crystalline phases. This is particularly relevant for MSL and Mars.
Article
Anorthosites exhibiting PDFs in quartz, ubiquitous undulatory extinction, and a mosaic-patchy extinction pattern in plagioclase suggest low peak pressures.
Article
Using empirical data gathered from scanning a calibration phantom it is possible to reduce or remove offending artifacts from previously collected data.
Article
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We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitati...
Article
A Mission Control Architecture is presented for a Robotic Lunar Sample Return Mission which builds upon the experience of the landed missions of the NASA Mars Exploration Program. This architecture consists of four separate processes working in parallel at Mission Control and achieving buy-in for plans sequentially instead of simultaneously from al...
Article
Recent observations of carbonate minerals in ancient Martian rocks have been interpreted as evidence for the former presence of circumneutral solutions optimal for carbonate precipitation. Sampling from surface and subsurface regions of the low-pH system of Río Tinto has shown, unexpectedly, that carbonates can form under diverse macroscopic physic...
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Enigmatic millimetre-scale micro-concretions with pseudocrystal faces and dominated by green clay minerals occur in unfossiliferous siliciclastic mudstone of the Lower Ordovician (479.0–466.0 Ma) Tonggao Formation, South China. The fossil-free mudstone unit is associated with local biodiversity decline. The mineralogy and mineral chemistry of these...
Conference Paper
In this contribution we present a case that impact craters on Early Mars would have represented prime habitats for life, and potentially for its origin, and that impact craters, therefore, should be prime exploration targets for future missions.
Article
The analysis of sulphur isotopic compositions in three sets of surface sulphate samples from the soil zone in the Haughton impact structure shows that they are distinct. They include surface gypsum crusts remobilized from the pre-impact gypsum bedrock (mean δ34S +31‰), efflorescent copiapite and fibroferrite associated with hydrothermal marcasite (...
Article
Basaltic hydrovolcanic tuffs from central Oregon illustrate how primary porosity and permeability control hydrothermal fluid flow and alteration assemblages.
Article
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Mineralogical data from surficial suevite, Nördlingen, and Wörnitzostheim drill cores used to assess the extent of the Ries post-impact hydrothermal system suggest that the system outside the crater rim is more extensive than previously reported.