Frédéric Candaudap

Evaluation of infrared femtosecond laser ablation for the analysis of geomaterials by ICP-MS

The capabilities of an infrared (IR) Ti:sapphire femtosecond laser (≈800 nm) to ablate and analyze geomaterials such as monazite, zircon and synthetic glass reference materials is evaluated, with emphasis on U/Pb ratio determinations useful for dating accessory minerals in rocks. We particularly discuss the influence of pulse duration (respectively 60, 200, 350, 500, 670, 830, 2000 and 3000 fs) on the internal precision (2 min ablation), reproducibility over two weeks and accuracy of quadrupole ICP-MS measurements. The best results for all these criteria are obtained when using the shortest pulse duration (60 fs). It was found that internal precision and reproducibility were improved by a factor of 3 and 4, respectively, from picosecond to 60 fs pulsewidths. Reproducibility at this pulse duration for U/Pb ratio determinations is of 2% RSD or better, depending on the material analyzed, and this ratio is accurate within this uncertainty. Lead isotopic ratios also benefit from the shortest pulsewidth. They are measured at 60 fs with a precision (<0.5% RSD) approaching the limitations of quadrupole ICP-MS. Preliminary data were also obtained using the 3rd harmonic (≈266 nm) of the Ti:sapphire fundamental wavelength and they are compared with the infrared mode. There seems to be no obvious analytical benefit to switch from IR to UV in the femtosecond laser ablation regime. Analyses of zircon 91500 with IR pulses led to better repeatability, around 0.9% (10 values, 1σ), compared to 3% for the UV pulses. The accuracy appears to be comparable for the two wavelengths.

Amorphous Materials: Properties, Structure, and Durability{dagger} Arsenic enrichment in hydrous peraluminous melts: Insights from femtosecond laser ablation-inductively coupled plasma-quadrupole mass spectrometry, and in situ X-ray absorption fine structure spectroscopy

Abstract Despite the ubiquity of arsenic in hydrothermal-magmatic environments, its abundance, distribution, and chemical and structural status in natural silicate melts and glasses remain poorly known. Here we report the first in situ measurements of the redox state and molecular structure of As, using X-ray absorption fine structure (XAFS) spectroscopy, in a rhyolitic peraluminous glass from Macusani (SE Peru) that is representative of anatectic melts derived from metasedimentary crustal protoliths. Arsenic abundances as well as the concentrations of other trace elements were measured in the glass using a femtosecond laser ablation-inductively coupled plasma-quadrupole mass spectrometry (LA-ICP-QMS). The glass shows enrichments, by factors of 10 to 100, in comparison with the mean continental crust values, for As and other incompatible trace elements (e.g., Be, B, Rb, Sn, Sb, and Ta), and by factors of 100 to 200 for Li, Cd, and Cs. Arsenic is present in the peraluminous glass in trivalent state in the form of oxy-hydroxide complexes like AsO(OH)2- and/or As(OH)3, similar to those dominant in the aqueous fluid vapor phases at hydrothermal-magmatic conditions. The similar As chemical speciation between the fluid and the melt is consistent with As fluid/melt partitioning coefficients close to one, as observed in experiments on rhyolite-water systems. The depolymerized melt structure caused by elevated H2O, F, and P contents is likely to allow accomodation of high concentrations of metalloid hydroxide/hydrated complexes. Consequently, hydrous silicate melts may be important transporting media in shallow magmatic-hydrothermal settings for As and similar elements like B and Sb due to their high affinity to water and hydroxide ligands

Tin and associated metal and metalloid geochemistry by femtosecond LA-ICP-QMS microanalysis of pegmatite–leucogranite melt and fluid inclusions: new evidence for melt–melt–fluid immiscibility

Abstract Granitic pegmatites are exceptional igneous rocks and the possible role of an immiscibility process in their origin is strongly debated. To investigate metal and metalloid behaviour in hydrous peraluminous systems (aluminium saturation index, ASI >1), we analysed 15 quartz-hosted primary melt and fluid inclusions from pegmatites in the Ehrenfriedersdorf Complex (Erzgebirge, Germany) and 26 primary melt inclusions from leucogranites of the Ehrenfriedersdorf district (Germany), Kymi (Finland) and Erongo (Namibia) by femtosecond laser ablation inductively coupled plasma quadrupole mass spectrometry. The results presented here for 32 elements provide evidence for metal and metalloid fractionation between two types of immiscible melts (A and B) and NaCl-HCl-rich brine in the pegmatite system. No evidence for the boundary layer effect was observed in the 40-500 pm size melt inclusions that were investigated. The data on the Ehrenfriedersdorf pegmatites allow quantification of the metal and metalloid partitioning between natural NaCl-rich brine and the two types of melt (e.g. Kbrine/type-A,BAs = 0.01 - 1.7; Kbrine/type-A,BAs = 10 - 285; Kbrine/type-A,BZn ≥ 50; Kbrine/type-A meltPb ≥ 50; Kbrine/type-A meltAg = 46. These data are in accord with existing natural and experimental data on equilibrium fluid-melt partitioning as well as spectroscopic data on the metal and metalloid complexation in hydrous aluminosilicate melts and NaCl-HCl-rich fluids.

Rare earth element analysis in natural waters by multiple isotope dilution – sector field ICP-MS

The rare earth elements (REEs) are valuable tracers in the earth, ocean and environmental sciences. Ten out of fourteen stable REEs have two or more isotopes, making them suitable for quantification by isotope dilution. We present a plasma mass spectrometry based multiple isotope dilution method for high precision REE concentration analysis in aqueous media. Key aspects of the method are: (i) flexible spiking of ten REEs via two LREE and HREE mixed spike solutions. (ii) Offline pre-concentration and matrix removal, by ion chromatography for freshwater samples and by iron co-precipitation or ion chromatography with the Nobias™ resin for seawater samples. (iii) High sensitivity detection by sector field-inductively coupled plasma mass spectrometry (SF-ICP-MS). (vi) The use of a desolvation micro-nebulization introduction system to lower polyatomic Ba and LREE-oxide interferences on HREEs. The method is suitable for a range of freshwater to seawater type samples, and was validated against SLRS-4, SLRS-5, and CASS-5 reference materials and two GEOTRACES marine inter-comparison samples. Long-term external precision on all REEs was <2% RSD, except La and Ce. Minimum sample volumes are 1 ml for freshwater and 50 ml for seawater. The multispike SF-ICP-MS method should be of particular interest in exploring subtle variations in aqueous REE fractionation patterns and anomalies in large numbers of samples.

REY-Th-U Solute Dynamics in the Critical Zone: Combined Influence of Chemical Weathering, Atmospheric Deposit Leaching and Vegetation Cycling (Mule Hole Watershed, South India)

The source and proportion of REY, Th and U exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the sub-humid tropical forested CZO of Mule Hole, Southern India. The study relies on a pluri-annual hydro-geochemical monitoring combined with a hydrological model. The significant difference between the soil input (SI) and output (SO) solute fluxes (mmol/km2/yr) of LREE (SI-SO = 13250-1500), HREE (1930-235), Th (64-12) and U (63-25) indicates a strong uptake by roots carried by canopy and forest floor processes. The contribution of atmospheric dust leaching can reach about 60% of LREE and 80% of HREE. At the watershed scale, the U solute flux exported by groundwater (180 mmol/km2/yr) mainly originates from the breakdown of primary U-bearing accessory minerals and dominates by a factor of 25 the stream flux. The precipitation of authigenic U bearing phases and adsorption onto Fe-oxides and oxyhydroxides plays a significant role for limiting the U mobility. In the groundwater, the plagioclase chemical weathering is efficiently traced by the positive Eu-anomaly. The very low (REY) to nil (Th) contents are explained by the precipitation of authigenic phases. In the stream flow, dominated by the overland flow (87% of the yearly stream flow), the solute exports (in mmol/km2/yr) of REY (1080 for LREE and 160 for HREE) and of Th (14) dominate those by groundwater. Their mobility is enhanced by chelation with organic ligands produced by forest floor and canopy processes.