Search results for "petrology"
showing 10 items of 1516 documents
Integrative analysis of the mineralogical and chemical composition of modern microbialites from ten Mexican lakes: What do we learn about their forma…
2021
International audience; Interpreting the environmental conditions under which ancient microbialites formed relies upon comparisons with modern analogues. This is why we need a detailed reference framework relating the chemical and mineralogical compositions of modern microbialites to the physical and chemical parameters prevailing in the environments where they form. Here, we measured the chemical, including major and trace elements, and mineralogical composition of microbialites from ten Mexican lakes as well as the chemical composition of the surrounding waters. Saturation states of lakes with different mineral phases were systematically determined and correlations between solution and so…
Neutron scattering and imaging: a tool for archaeological studies
2015
International audience; Neutron scattering and neutron imaging are powerful techniques for studying the structure of objects without damage, which is an essential prerequisite for investigations in Cultural Heritage domain, particularly in Archaeology. The deep penetration of neutrons in most materials allows for the study of relatively large objects. The contrast between similar materials, like metals in alloys, or that due to the presence of hydrogen atoms gives information about the internal structure of objects that have been modified or repaired in the past. Imaging and tomography give a 3-dimensional view of the whole object, permitting discrimination between different parts of the ob…
X-ray diffraction Warren–Averbach mullite analysis in whiteware porcelains: influence of kaolin raw material
2018
ABSTRACTCompositional and microstructural analysis of mullites in porcelain whitewares obtained by the firing of two blends of identical triaxial composition using a kaolin B consisting of ‘higher-crystallinity’ kaolinite or a finer halloysitic kaolin M of lower crystal order was performed. No significant changes in the average Al2O3 contents (near the stoichiometric composition 3:2) of the mullites were observed. Fast and slow firing at the same temperature using B or M kaolin yielded different mullite contents. The Warren–Averbach method showed increase of the D110 mullite crystallite size and crystallite size distributions with small shifts to greater values with increasing firing temper…
Exomorphism of jacobsite precipitates in bixbyite single crystals from the Thomas Range in Utah
2021
Abstract Naturally occurring single crystals of bixbyite, (Fe,Mn)2O3, from the Thomas Mountain Range in Utah, U.S.A., were studied via (scanning) transmission electron microscopy (S)TEM. With up to 5 cm edge length, these mineral specimens are the largest bixbyite crystals found worldwide. Their hexahedral shapes are often modified by {211} facets at the corners and small {211} truncations along their cube edges. Characteristic lamellar defects, running parallel to the {100} planes, can be observed via TEM imaging. The defects are, according to EDS analyses, attributed to the tetragonal manganese silicate braunite, Mn7[SiO12]. In the present study, electron nano-diffraction and atomic resol…
A New LA ‐ ICP ‐ MS Method for Ti in Quartz: Implications and Application to High Pressure Rutile‐Quartz Veins from the Czech Erzgebirge
2016
Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti-in-quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining 48Ti mass fractions in quartz by LA-ICP-MS at the 1 μg g−1 level, relevant to quartz in HP-LT terranes. We suggest that natural quartz such as the low-CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g−1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are i…
Diagenetic stability of non-traditional stable isotope systems (Ca, Sr, Mg, Zn) in teeth – An in-vitro alteration experiment of biogenic apatite in i…
2021
Stable isotope ratios and trace element concentrations of fossil bones and teeth are important geochemical proxies for the reconstruction of diet and past environment in archaeology and palaeontology. However, since diagenesis can significantly alter primary diet-related isotope signatures and elemental compositions, it is important to understand and quantify alteration processes. Here, we present the results of in-vitro alteration experiments of dental tissues from a modern African elephant molar reacted in aqueous solutions at 30 °C and 90 °C for 4 to 63 days. Dental cubes with ≈ 3 mm edge length, comprising both enamel and dentin, were placed into 2 mL of acidic aqueous sol…
Partitioning of nitrogen during melting and recycling in subduction zones and the evolution of atmospheric nitrogen
2019
Abstract The subduction of sediment connects the surface nitrogen cycle to that of the deep Earth. To understand the evolution of nitrogen in the atmosphere, the behavior of nitrogen during the subduction and melting of subducted sediments has to be estimated. This study presents high-pressure experimental measurements of the partitioning of nitrogen during the melting of sediments at sub-arc depths. For quantitative analysis of nitrogen in minerals and glasses, we calibrated the electron probe micro-analyzer on synthetic ammonium feldspar to measure nitrogen concentrations as low as 500 μg g−1. Nitrogen abundances in melt and mica are used together with mass balance calculations to determi…
Constraining electric resistivity tomography by direct push electric conductivity logs and vibracores: An exemplary study of the Fiume Morto silted r…
2018
The inversion of geoelectric data is nonunique. Therefore, electric resistivity tomography (ERT) usually results in different subsurface models that fit observed apparent resistivity values equally well. To reduce the uncertainty, constraints on the geometry and resistivity of subsurface structures can be incorporated into the ERT inversion. We test different ways of constraining ERT by applying (1) improved starting models, (2) structural constraints, and (3) structural and resistivity constraints. A priori information is needed for these approaches, which is acquired from direct push electrical conductivity (DP-EC) logs and vibracores in our study. We found that adapting high vertical re…
Subduction or sagduction? Ambiguity in constraining the origin of ultramafic–mafic bodies in the Archean crust of NW Scotland
2016
Abstract The Lewisian Complex of NW Scotland is a fragment of the North Atlantic Craton. It comprises mostly Archean tonalite–trondhjemite–granodiorite (TTG) orthogneisses that were variably metamorphosed and reworked in the late Neoarchean to Paleoproterozoic. Within the granulite facies central region of the mainland Lewisian Complex, discontinuous belts composed of ultramafic–mafic rocks and structurally overlying garnet–biotite gneiss (brown gneiss) are spatially associated with steeply-inclined amphibolite facies shear zones that have been interpreted as terrane boundaries. Interpretation of the primary chemical composition of these rocks is complicated by partial melting and melt loss…
Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu)
2020
Abstract Open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux, largely through passive degassing and mild explosive activity. We present volcanic gas flux and composition data from Yasur Volcano, Vanuatu collected in July 2018. The average volcanic plume chemistry is characterised by a mean molar CO2/SO2 ratio of 2.14, H2O/SO2 of 148 and SO2/HCl of 1.02. The measured mean SO2 flux in the period of 6th to 9th July is 4.9 kg s−1. Therefore, the mean fluxes of the other species are 7.5 kg∙s−1 CO2, 208 kg∙s−1 H2O and 4.8 kg∙s−1 HCl. The degassing regime at Yasur volcano ranges from ‘passive’ to ‘active’ styles, with the latter including Stromb…