The source of A-type magmas in two contrasting settings: U–Pb, Lu–Hf and Re–Os isotopic constraints

The sources of post-orogenic A-type magmas from two distinct geodynamic settings are compared. The end of the ca. 514–480 Ma Delamerian Orogeny, southeastern South Australia, was marked by ~ 10 Myr of bimodal A-type magmatism, driven by convective removal of thickened lithosphere. Initial Os and Hf isotope ratios record a heterogeneous lithospheric mantle source, with some input from aesthenospheric mantle. Mafic parental melts fractionated to produce the granites. In contrast, initial Os isotope ratios of the A-type magmas that comprise the ca. 1598–1583 Ma Mesoproterozoic Gawler Felsic Large Igneous Province, central South Australia, record a dominant evolved lower crust component. However, initial Hf isotope ratios from these samples are depleted, indicating a mantle source for lithophile elements. This voluminous, bimodal magmatism lasted for ~ 15 Myr, and ended the Wartakan Orogeny. In both cases the homogenisation of chemical (rheological) heterogeneities, inherited from terrain amalgamation and orogenic thickening, strengthened the lithosphere. The contemporaneous fusion of heterogeneous mantle ± crust may represent a common, stabilising influence on the lithospheric column regardless of tectono-magmatic setting

Comparison between LA-ICP-MS and EPMA analysis of trace elements in diamonds

Eight elements were measured in twenty-eight microinclusion-bearing diamonds using both Electron Probe Micro-Analyzer (EPMA) and the cellulose-calibrated Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) methods. Orthopyroxene microinclusions (< 1μm) found in one of the diamonds have very similar Si atoms per formula unit and Mg/(Mg + Fe) ratios to those of larger orthopyroxene inclusions in diamonds, indicating that the EPMA analysis of the major elements in individual mineral and fluid microinclusions is accurate to better than 15%. For the fluid-bearing diamonds, very good correlations were found between the element/Fe ratios determined by EPMA and LA-ICP-MS for Mg, Ca, Na and K and most diamonds fall on or close to the 1:1 line, validating the accuracy of both techniques. Al/Fe, Ti/Fe and Ba/Fe ratios show good to moderate correlations. LA-ICP-MS analyses of four coated diamonds show that concentrations in the microinclusion-bearing coat are higher than those in the clear core by two orders of magnitude or more. Since most interferences from C-N-O-H molecular ions can be corrected by reference to analyses of pure synthetic diamond, and fewer interferences are expected for the heavier trace elements, the assembled information suggests that LA-ICP-MS technique combined with the cellulose calibration method provides accurate trace-element analyses of diamonds and allows compositional characterization of fluids trapped in them.11 page(s

Evaluation of perchloric versus nitric acid digestion for precise determination of trace and ultra trace elements by ICP-MS

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Trace element and isotopic composition of GJ-red zircon standard by laser ablation

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Spatial distribution of lead in human primary teeth as a biomarker of pre- and neonatal lead exposure

Lead remains one of the most hazardous toxins in our environment. Because the toxic effects of lead are most prominent during early development, it is important to develop a suitable biomarker for lead exposure during the pre- and neonatal periods. In the present study, the spatial distribution of lead was measured in the enamel and dentine of ten human primary teeth using laser ablation-inductively coupled plasma-mass spectrometry. The neonatal line, visualized using confocal laser scanning microscopy, was used to demarcate the pre- and postnatal regions of the sample teeth. Lead levels in pre- and postnatally formed enamel and dentine were compared to blood-lead levels measured at birth and one year of age for four of these participants. Mean dentine-lead levels ranged from 0.17 ± 0.02 to 5.60 ± 1.79 μg/g, and mean enamel-lead levels ranged from 0.04 ± 0.01 to 1.47 ± 0.20 μg/g. The results of this preliminary study showed that the spatial distribution of lead in dentine reflected the blood-lead levels. The present study demonstrates a methodology where the spatial distribution of lead in the dentine of human primary teeth may be used to obtain temporal information of environmental lead exposure during the pre- and neonatal periods.8 page(s