Experimental variable effects on laser heating of inclusions during Raman spectroscopic analysis

Raman spectroscopy for fluid, melt, and mineral inclusions provides direct insight into the physicochemical conditions of the environment surrounding the host mineral at the time of trapping. However, the obtained Raman spectral characteristics such as peak position are modified because of local temperature enhancement of the inclusions by the excitation laser, which might engender systematic errors and incorrect conclusions if the effect is not corrected. Despite the potentially non-negligible effects of laser heating, the laser heating coefficient (B) (°C/mW) of inclusions has remained unsolved. For this study, we found B from experiments and heat transport simulation to evaluate how various parameters such as experimental conditions, mineral properties, and inclusion geometry affect B of inclusions. To assess the parameters influencing laser heating, we measured B of a total of 19 CO2-rich fluid inclusions hosted in olivine, orthopyroxene, clinopyroxene, spinel, and quartz. Our results revealed that the measured B of fluid inclusions in spinel is highest (approx. 6 °C/mW) and that of quartz is lowest (approx. 1 × 10−2 °C/mW), consistent with earlier inferences. Our simulation results show that the absorption coefficient of the host mineral is correlated linearly with B. It is the most influential parameter when the absorption coefficient of the host mineral (αh) is larger than that of an inclusion (αinc). Furthermore, although our results indicate that both the inclusion size and depth have little effect on B if αh > αinc, the thickness and radius of the host mineral slightly influence B. These results suggest that the choice of inclusion size and depth to be analyzed in a given sample do not cause any systematic error in the Raman data because of laser heating, but the host radius and thickness, which can be adjusted to some degree at the time of sample preparation, can cause systematic errors between samples.Our results demonstrate that, even with laser power of 10 mW, which is typical for inclusion analysis, the inclusion temperature rises to tens or hundreds of degrees during the analysis, depending especially on the host mineral geometry and optical properties. Therefore, correction of the heating effects will be necessary to obtain reliable data from Raman spectroscopic analysis of inclusions. This paper presents some correction methods for non-negligible effects of laser heating

Body iron metabolism and pathophysiology of iron overload

Iron is an essential metal for the body, while excess iron accumulation causes organ dysfunction through the production of reactive oxygen species. There is a sophisticated balance of body iron metabolism of storage and transport, which is regulated by several factors including the newly identified peptide hepcidin. As there is no passive excretory mechanism of iron, iron is easily accumulated when exogenous iron is loaded by hereditary factors, repeated transfusions, and other diseased conditions. The free irons, non-transferrin-bound iron, and labile plasma iron in the circulation, and the labile iron pool within the cells, are responsible for iron toxicity. The characteristic features of advanced iron overload are failure of vital organs such as liver and heart in addition to endocrine dysfunctions. For the estimation of body iron, there are direct and indirect methods available. Serum ferritin is the most convenient and widely available modality, even though its specificity is sometimes problematic. Recently, new physical detection methods using magnetic resonance imaging and superconducting quantum interference devices have become available to estimate iron concentration in liver and myocardium. The widely used application of iron chelators with high compliance will resolve the problems of organ dysfunction by excess iron and improve patient outcomes

Temperature dependence of a Raman CO2 densimeter from 23 degrees C to 200 degrees C and 7.2 to 248.7 MPa : Evaluation of density underestimation by laser heating

Unintended local temperature enhancement by excitation laser might change Raman spectral features and potentially lead to misinterpretation of the data. To evaluate robustness of Raman CO2 densimeters in the presence of laser heating, we investigate the relation between temperature (T, degrees C), density (rho, g/cm(3)), and Fermi diad split (Delta, cm(-1)) using a high-pressure optical cell at 23 degrees C to 200 degrees C and 7.2-248.7 MPa. Results indicate that Delta decreases concomitantly with increasing temperature for a constant density in all density regions investigated. This result suggests that the density estimated based on Delta might be underestimated if the fluid is heated locally by the laser. Combining results of earlier studies with those of the present study indicates that the temperature dependence of Delta (|( partial differential Delta/ partial differential T)(rho)|) has a maximum value around 0.6-0.7 g/cm(3). Consequently, at very high densities such as 1.1-1.2 g/cm(3), |( partial differential Delta/ partial differential T)(rho)| is small. Thus, Delta at such densities is less affected by laser heating. However, at densities below approximately 0.7 g/cm(3), although |( partial differential Delta/ partial differential T)(rho)| becomes smaller at lower densities, the relative density decrease becomes larger even for a small density decrease because the density itself becomes smaller. Therefore, at such densities, a density decrease of more than 10% was observed for some fluid inclusions, even at typical laser powers for inclusion analysis. Finally, to accurately estimate the density even in the presence of laser heating, we show that it is effective to estimate the intercept Delta from the correlation between Delta and laser power and substitute it into Delta-rho relations

Characterization of oxide assemblages of a suite of granulites from Eastern Ghats Belt, India: implication to the evolution of C-O-H-F fluids during retrogression

We document complex intergrowth involving spinel-ilmenite-magnetite-hematite-corundum-rutile in various combinations from a suite of granulite facies rocks of Eastern Ghats Belt, India. Individual oxide phase shows considerable compositional variation among textures and samples. These textures arguably developed by oxidation reaction of early spinel and ilmenite solid solution from near-peak to subsequent retrogressive stages. Oxygen fugacity is measured at a constant pressure of 8 kbar and different temperatures estimated from geothermometric analyses involving oxide and silicate-bearing equilibria in different samples. The calculated fO<SUB>2</SUB> values are 2-3 log units higher than the QFM buffer except for one sample. Uncertainties in fO<SUB>2</SUB> calculation in some samples arise presumably due to extensive compositional readjustment of different oxide systematics at lower temperatures. The persistence of high fO<SUB>2</SUB> in mineral assemblages could be inherited from an oxidized precursor, but field evidence and presence of H<SUB>2</SUB>O-CO<SUB>2</SUB>-rich fluid inclusions in the studied samples imply possible involvement of externally-derived oxidizing fluid in the later part of the retrograde history. Recent experimental and natural data suggest CO<SUB>2</SUB> charged brine solution could be suitable for oxidation of mineral assemblages. Presence of brine inclusions are not detected, but fluorine enriched nature of biotite grains could possibly provide some indication for its presence. The mixed fluid possibly has its source in the crystallizing mafic magma emplaced at the lower crust that is exposed in the adjacent area