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Abstract: Nakhlites are martian pyroxenites that crystallized in a shallow intrusion or lava flow(s) during the Amazonian period, ~1.3 Ga [1]. They host amorphous and/or nanocrystalline hydrous Fe,Mg-silicates and a range of salt minerals that clearly formed via water-rock interactions in the subsurface of Mars [e.g., 2,3,4] as recently as ~680 Ma [5]. The nature of the aqueous event(s) that triggered the alterations, especially the mechanisms by which the secondary minerals formed are, however, not fully recognized. The most comprehensive model suggests that all the secondary minerals were formed by a single episodic event and were deposited from a brine that was derived from a low-T hydrothermal source [6]. Trace element signatures of some alteration minerals [3] may in turn suggest evaporation of a surface derived brine such as flood waters. Nanostructural studies [4] instead reveal that carbonates may have formed by serpentinization and carbonation of olivine via reaction with atmosphericderived gas. The majority of interpretations are, however, based mainly on the observation of Fe,Mg-silicates, while the salt minerals, and especially their textures, have been studied far less. Our study is concerned with the reconstruction of fluid flow(s) and alteration/replacement histories recorded by the salt minerals in nakhlites. We focus on their chemical and textural relationships to the primary minerals, each other, the hydrous Fe,Mg-silicates and the fracture systems. Moreover, we have undertaken this study with no (or minimal) invasive or destructive sampling.

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Abstract: Measuring the low bromine abundances in Earth’s materials remains an important challenge in order to constrain the geodynamical cycle of this element. Suitable standard materials are therefore required to establish reliable analytical methods to quantify Br abundances. In this study we characterise 21 Br-doped glasses synthesized from natural volcanic rocks of mafic to silicic compositions, in order to produce a new set of standards for Br analyses using various techniques. The nominal Br contents (amounts of Br loaded in the experimental samples) of 15 of 21 glasses were confirmed within 20% by instrumental neutron activation analysis (INAA). Using this new set of standards, we compare three micro-analytical approaches to measure Br contents in silicate glasses: synchrotron X-ray fluorescence (SR-XRF), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS). With SR-XRF, the Br contents of the standard glasses were determined with the highest accuracy (< 10% for Br ≥ 10 ppm; > 25% for Br ≤ 5 ppm), and high precision (< 10% for Br contents > 10 ppm; 20-30% for Br ≤ 10 ppm). The detection limit was estimated to be less than 1 ppm Br. All those factors combined with a high spatial resolution (5x5 μm for the presented measurements), means that SR-XRF is well suited to determine the low Br abundance in natural volcanic glasses (crystal-hosted melt inclusions or matrix glasses of crystallized samples). At its current stage of development, the LA-ICP-MS method allows the measurement of hundreds to thousands ppm Br in silicate glasses with a precision and accuracy generally within 20 %. The Br detection limit of this method has not been estimated but its low spatial resolution (90 μm) currently prevents its use to characterise natural volcanic glasses, however it is fully appropriate to analyse super liquidus or sparsely phyric, Br-rich experimental charges. Our study shows that SIMS appears to be a promising technique to measure the low Br contents of natural volcanic glasses. Its spatial resolution is relatively good (~ 15 μm) and, similarly to SR-XRF, the detection limit is estimated to be ≤ 1 ppm. Using our new set of standards, the Br contents of two MPI-DING reference glasses containing less than 1.2 ppm of Br were reproduced with precision < 5% and accuracy < 20%. Moreover, SIMS presents the advantage of being a more accessible instrument than SR-XRF and data processing is more straightforward.

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Abstract: Despite regulation, brain iron increases with aging and may enhance aging processes including neuroinflammation. Increases in magnetic resonance imaging transverse relaxation rates, R2 and R2*, in the brain have been observed during aging. We show R2 and R2* correlate well with iron content via direct correlation to semi-quantitative synchrotron-based X-ray fluorescence iron mapping, with age-associated R2 and R2* increases reflecting iron accumulation. Iron accumulation was concomitant with increased ferritin immunoreactivity in basal ganglia regions except in the substantia nigra (SN). The unexpected dissociation of iron accumulation from ferritin-upregulation in the SN suggests iron dyshomeostasis in the SN. Occurring alongside microgliosis and astrogliosis, iron dyshomeotasis may contribute to the particular vulnerability of the SN. Dietary restriction (DR) has long been touted to ameliorate brain aging and we show DR attenuated age-related in vivo R2 increases in the SN over ages 7 – 19 months, concomitant with normal iron-induction of ferritin expression and decreased microgliosis. Iron is known to induce microgliosis and conversely, microgliosis can induce iron accumulation, which of these may be the initial pathological aging event warrants further investigation. We suggest iron chelation therapies and anti-inflammatory treatments may be putative ‘anti-brain aging’ therapies and combining these strategies may be synergistic.

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Abstract: Transition metal concentrations in the central nervous system (CNS) are altered in neurodegenerative diseases such as Alzheimer’s, Parkinson’s and multiple sclerosis. A common symptom of these diseases is demyelination, which is the degradation of the myelin sheath that encapsulates the neurons in vertebrates. Transition metal concentrations were measured in Long Evans Shaker (LES) rodent model and compared to healthy age-matched controls to investigate the relationship between transition metals and myelination. Micro probe Synchrotron Radiation X-ray Fluorescence (µSRXRF) was used to measure concentrations of manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn) in regions of grey matter and white matter in Shaker rodents and their age-matched Long Evans (LE) controls in the cerebellum and spinal cord. In the cerebellum, the concentrations of all elements were significantly increased in the white matter of the Shaker model, and decreased in the gray matter of the Shaker model in comparison to their age and region matched controls. In the spinal cord samples, concentrations of all metals were higher in white matter and grey matter of Shaker rat spinal cord compared to those in the control rat spinal cord. This study demonstrated that the sensitivity of µSRXRF is sufficient to discriminate between the elemental distributions of gray and white matter of the brain sections and spinal cords in the two groups. The observed significant increase of Mn, Fe, Zn and Cu in the white matter of the Shaker animals in the cerebellum and spinal cord compared to controls could be the result of astrocytic glial cells replacing the myelin in the CNS. Unlike other imaging techniques, the fine resolution of µSRXRF enables specific regions of gray matter structures namely, the molecular layer and the granule layer to be identified in the rat CNS, and their transition metal concentrations to be quantified. This work will further establish µSRXRF as a powerful analytic technique for compositional studies in brain sections from models of brain disease.

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Abstract: A model of dysmyelination, the Long Evans Shaker (les) rat, was used to study the contribution of myelin to MR tissue properties in white matter. A large region of white matter was identified in the deep cerebellum and was used for measurements of the MR relaxation rate constants, R1 = 1/T1 and R2 = 1/T2, at 7 T. In this study, R1 of the les deep cerebellar white matter was found to be 0.55 ± 0.08 s –1 and R2 was found to be 15 ± 1 s–1, revealing significantly lower R1 and R2 in les white matter relative to wild-type (wt: R1 = 0.69 ± 0.05 s–1 and R2 = 18 ± 1 s–1). These deviated from the expected ΔR1 and ΔR2 values, given a complete lack of myelin in the les white matter, derived from the literature using values of myelin relaxivity, and we suspect that metals could play a significant role. The absolute concentrations of the paramagnetic transition metals iron (Fe) and manganese (Mn) were measured by a micro-synchrotron radiation X-ray fluorescence (μSRXRF) technique, with significantly greater Fe and Mn in les white matter than in wt (in units of μg [metal]/g [wet weight tissue]: les: Fe concentration,19 ± 1; Mn concentration, 0.71 ± 0.04; wt: Fe concentration,10 ± 1; Mn concentration, 0.47 ± 0.04). These changes in Fe and Mn could explain the deviations in R1 and R2 from the expected values in white matter. Although it was found that the influence of myelin still dominates R1 and R2 in wt rats, there were non-negligible changes in the contribution of the metals to relaxation. Although there are already problems with the estimation of myelin from R1 and R2 changes in disease models with pathology that also affects the relaxation rate constants, this study points to a specific pitfall in the estimation of changes in myelin in diseases or models with disrupted concentrations of paramagnetic transition metals. Copyright © 2016 John Wiley & Sons, Ltd.