Search results for "AMA"
showing 10 items of 8558 documents
Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls
2008
AbstractVaterite and aragonite polymorphs in freshwater cultured pearls from mussels of the genus Hyriopsis (Unionidae) were structurally and compositionally characterized by Raman spectroscopy, Micro computer tomography, high resolution field emission scanning electron microscopy, electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry. The appearance of vaterite in pearls is related to the initial stages of biomineralization, although we demonstrate that vaterite can not be a precursor to aragonite. It is not related to a particular crystal habit and therefore does not have a structural functionality in the pearls. Larger contents of elements typically…
Effects of natural radiation damage on back-scattered electron images of single crystals of minerals
2006
Generally, it has been assumed that signal intensity variations in back-scattered electron (BSE) images of minerals are mainly controlled by chemical heterogeneity. This is especially true for images of single crystals, where effects of different crystal orientations with respect to the incident beam on the observed BSE are excluded. In contrast, we show that local variations of the structural state within single-crystals (i.e., degree of lattice order or lattice imperfectness) may also have dramatic effects on the back-scattering of electrons. As an example, we present BSE images of single-crystals of natural zircon, ZrSiO 4 , whose intensity patterns are predominantly controlled by struct…
Trends in global research in deforestation. A bibliometric analysis
2018
The main aim of this study was to analyse topics of research, scientific production, collaboration among countries, and most cited papers on deforestation through a bibliometric and social network study of articles found in the Web of Science database. The most productive subject areas corresponded to Environmental Sciences, Ecology and Environmental Studies. The articles were published in 458 different journals. A total of 2051 research articles were obtained. The main challenges identified for deforestation include “land use change” “conservation” “climate change” “rain forest” and “reducing emissions from deforestation and degradation”. Social and economic topics are understudied. An imp…
Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)
2018
Abstract The Kane Megamullion oceanic core complex located along the Mid-Atlantic Ridge (23°30′N, 45°20′W) exposes lower crust and upper mantle directly on the ocean floor. We studied chalcophile elements and sulfides in the ultramafic and mafic rocks of the crust-mantle transition and the mantle underneath. We determined mineralogical and elemental composition and the Cu isotope composition of the respective sulfides along with the mineralogical and elemental composition of the respective serpentines. The rocks of the crust-mantle transition zone (i.e., plagioclase harzburgite, peridotite-gabbro contacts, and dunite) overlaid by troctolites are by one order of magnitude enriched in several…
Carbon isotope composition of CO2-rich inclusions in cumulate-forming mantle minerals from Stromboli volcano (Italy)
2017
We report on measurements of concentration and carbon isotope composition (δ13CCO2) of CO2 trapped in fluid inclusions of olivine and clinopyroxene crystals separated from San Bartolo ultramafic cumulate Xenoliths (SBX) formed at mantle depth (i.e., beneath a shallow Moho supposed to be at 14.8 km). These cumulates, erupted about 2 ka ago at Stromboli volcano (Italy), have been already investigated by Martelli et al. (2014) mainly for Sr-Nd isotopes and for their noble gases geochemistry. The concentration of CO2 varies of one order of magnitude from 3.8·10− 8 mol g− 1 to 4.8·10− 7 mol g− 1, with δ13C values between − 2.8‰ and − 1.5‰ vs V-PDB. These values overlap the range of measurements …
Calculating pressure with elastic geobarometry: A comparison of different elastic solutions with application to a calc-silicate gneiss from the Rhodo…
2020
Abstract Raman elastic geobarometry has increasingly been used complementary to metamorphic phase equilibria to estimate the conditions of recrystallization in metamorphic rocks. The procedure of applying Raman elastic barometry to host-inclusion mineral systems requires several steps that involve various assumptions. One of the most essential assumptions is that the mineral host-inclusion system behaves in an elastic and reversible manner. We discuss the discrepant results obtained by different authors employing different analytical solutions for elasticity and explore the assumptions lying behind each method. Furthermore, we evaluate numerically linear and non-linear elastic solutions and…
Geochemistry of ultramafic and mafic rocks from the northern Central Asian Orogenic Belt (Tuva, Central Asia) - constraints on lower and middle arc c…
2021
Abstract The Agardagh Tes-Chem complex (ATCC) in Tuva, Central Asia (50.5°N, 95°E) exposes a rare mafic to ultramafic crust-mantle fragment that developed within a late Neoproterozoic (~570 Ma) intra-oceanic island arc system that was accreted to the Tuva-Mongolian microcontinent during the formation of the Central Asian Orogenic Belt. Residual mantle rocks (harzburgites and dunites) are highly refractory with high Cr# (0.59–0.83) and intermediate Mg# (0.46–0.52) in spinel and experienced high degrees of total melt extraction (up to 25%). In ultramafic cumulate rocks (wehrlites and pyroxenites), Cr# and Mg# in spinel are distinctly lower (0.22–0.45 and 0.34–0.37), and rare earth element (RE…
A Cloud masking algorithm for the XBAER aerosol retrieval using MERIS data
2017
Abstract To determine aerosol optical thickness, AOT, and other geophysical parameters describing conditions in the atmosphere and at the earth's surface by inversion of remote sensing measurements from space based instrumentation, it is necessary to separate ground scenes into cloud free and cloudy or cloud contaminated. Identifying the presence of cloud in a ground scene and establishing an accurate and adequate cloud mask is a challenging task. In this study, measurements by the European Space Agency (ESA) MEdium Resolution Imaging Spectrometer (MERIS) have been used to develop a cloud identification and cloud mask algorithm for preprocessing prior to application of the new algorithm cal…
Long-term stability of alpha particle damage in natural zircon
2005
Abstract We report the first discovery of radiation damage haloes generated by alpha particles in zircon. Proterozoic zircon crystals from a potassium-rich leucogranite from the Adirondack Mountains, New York State, have interior regions that are generally low in actinide elements (UO 2 + ThO 2 ≤ 0.02 wt.%) but show a remarkable pattern of heterogeneous metamictisation. The degree of radiation damage in these regions is not uniformly low, as would be expected if it corresponded to the observed actinide distribution patterns and age of the crystals. Rather, radiation damage is significantly increased in the outermost micro-areas of the low-actinide regions. The additional radiation damage …
Determination of water speciation in hydrous haplogranitic glasses with partial Raman spectra
2020
Abstract We use a mathematical approach to decompose the Raman water band at 3000 cm−1 to 3750 cm−1 into two partial Raman spectra corresponding to the individual Raman activity of the two water species, i.e., molecular water (H2Om) and OH-groups, present in hydrous rhyolitic glasses. The approach is based on a least-squares optimization algorithm and the assumption that the water band can be expressed as a linear combination of two partial Raman spectra. Our model makes no assumptions regarding the shape of the partial Raman spectra. The model input consists of about 700 Raman spectra from hydrous haplogranitic (HPG8) compositions with total water contents from 0.6 to 3.1 wt% and with know…