LA-ICPMS

We report experiments on optimisation of LA-ICP-MS mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals. The experimental design was refined with maps on clinopyroxene and amphibole macrocrysts (mainly antecrysts) from a porphyritic lamprophyre in NE Spain, as well as on a high precision metal wire grid. In terms of spatial resolution, we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0.4 and 0.7 μm of material, depending on ablation parameters. Maps were produced with square laser beam spots of 12 and 24 μm. It was found that complexities can be resolved in the sample even though they are smaller than the beam diameter (e.g., 7–10 μm discontinuities using 12 μm laser beam). Resolution in x and y was found to be identical, probably reflecting the fast washout of the two-volume ablation cell and the short total dwell time of the analyte menu selected. Due to the excellent stage reproducibility and the limited ablation depth, it is feasible to re-ablate the identical map area many times employing different instrument parameters or analyte menus. On the magmatic crystals, LA-ICP-MS maps define very sharp compositional zoning in trace elements, highlighting complex crystallisation histories where 'normal' magmatic fractionation is not the only process. Events of mafic recharge are easily recognised as zones enriched in compatible metals such as Cr, Ni or Sc. Further, trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data. These include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones. Therefore, LA-ICP-MS mapping opens a new window of opportunity for analysis of magmatic histories. The wide combination of instrumental parameters, such as laser beam size, scan speed and repetition rate, make it possible to carry out experiments at different levels of detail. We recommend a two-step approach to mapping. The initial step involves rapid maps to gain an overview of potential complexities in the sample; this enhances representativeness of the analysed materials, as a large number of crystals and trace elements can be tested in little time. Subsequently, detailed maps can be carried out on areas of interest. An additional function-ality is to create 1D-profiles from 2D-maps. The potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond.

The origin of salinity in crustal fluids can be deduced from their Cl, Br and Na concentrations and associated Cl/Br and Na/Br ratios. Here, a protocol for quantitative analysis of Cl, Br and Na concentration in individual fluid inclusions of variable size, bulk salinity, Cl, Br and Na contents is presented. It combines microthermometry and laser ablation — inductively coupled plasma mass spectrometry (LA-ICPMS) analysis.The method is based on: (i) microthermometric measurement of ice melting, hydrate melting, halite dissolution and sylvite dissolution temperatures in fluid inclusions; (ii) calibration of LA-ICPMS signals of Br by analyzing Na–Br–Cl standard solutions loaded in silica glass capillaries; (iii) calculation of solute (Cl, Na, Ca, K, Mg) concentration based on LA-ICPMS intensities and the Pitzer thermodynamic model (for inclusions of salinity below 23 wt.% equivalent NaCl), or a charge-balance approach (for higher salinity inclusions) and (iv) calculation of uncertainty on Cl, Br and Na concentration and Cl/Br and Na/Br ratios in the fluid.This method is applied to natural fluid inclusions with variable Cl, Br and Na contents as previously determined by microthermometry and bulk crush-leach coupled with ion chromatography analysis. The studied materials consist of: i) low-salinity inclusions from Alpine quartz veins and ii) high-salinity inclusions from the Trimouns talc deposit and from Athabasca Basin uranium deposits. Molar Cl/Br and Na/Br ratios range from 140 ± 50 to 1200 ± 400 and 17 ± 6 to 880 ± 290 in the analyzed inclusions. The calculated uncertainty on Cl/Br and Na/Br ratios in individual fluid inclusions is between 30 and 38%, regardless of the salinity. It appears that the analysis of individual inclusions coupled with uncertainty calculation allows the identification of significant variation of Cl/Br and Na/Br ratios within individual samples that could not be identified from previous bulk crush-leach and ion chromatography analyses. Because Br is a minor solute (molar Cl/Br is between ~ 100 and ~ 10000 in most crustal fluids), and because of its high first ionization energy, the determination of Br concentration in individual inclusion by combining microthermometry and LA-ICPMS analysis is most readily achievable for large (> 50 μm in diameter) inclusions. For smaller inclusions (10 to 50 μm in diameter), the applicability of the present method is more sensitive to the Br concentration.

Apatite is an important common U-and Th-bearing accessory mineral in igneous, metamorphic and clastic sed-imentary rocks. The advent of in situ U–Th–Pb apatite geochronology by the SIMS and LA-(MC)-ICP-MS methods has demonstrated the importance of having uniform and homogeneous reference materials. Recently, it has been shown that Sr and Nd isotopic data combined with U–Pb age and trace element concentration data can provide important constraints on apatite paragenesis because this phase usually exhibits high Sr and REE concentrations but has low Rb/Sr ratios which result in negligible corrections for the ingrowth of radiogenic Sr. However, as ap-atite can potentially have complex internal structures resulting from multiple thermal events, such as inherited cores and metamorphic overgrowths, requires that the Sr and Nd isotopic data should be measured with high spatial resolution. However isobaric interferences hamper the precise determination of Sr or Nd isotopic compositions in LA-MC-ICP-MS analysis. In this work we undertook in situ measurements of Sr and Nd isotopic compositions of eleven apatite reference materials (AP1, AP2, Durango, MAD, Otter Lake, NW-1, Slyudyanka, UWA-1, Mud Tank, McClure Mountain and SDG) commonly used in U–Th–Pb geochronology. Our obtained Sr and Sm– Nd isotopic compositions for these apatite samples are consistent with those values obtained by solution-based methods (isotope dilution and ion chromatography) using MC-ICP-MS or TIMS, which demonstrates the reliability and robustness of our analytical protocol.

The Western Irish Namurian Basin (WINB) preserves classic examples of basin floor sequences through to slope deposits and deltaic cyclothems. Despite over 50 years of research into the WINB, its sediment provenance remains highly contested. Sedimentological arguments, including palaeocurrent vectors and palaeoslope indicators have been invoked to propose a sediment source from the NW or the west (i.e. from within Laurentia). These same indicators have been subsequently reinterpreted to reflect a southern provenance. It is not clear from sedimentological arguments alone which interpretation more accurately reflects the infilling of the WINB. Regional-scale constraints on WINB provenance may be obtained with detrital zircon U–Pb geochronology.U–Pb LA-ICP-MS detrital zircon analysis was undertaken on samples from three sandstone units at different stratigraphic levels within the WINB siliciclastic sedimentary fill (Ross Formation, Tullig Sandstone, Doonlicky Sandstone). The samples are dominated by 500–700 Ma zircons, which can be correlated with Cadomian–Avalonian orogenic activity within terranes to the south of the WINB (Avalonia/Ganderia, Armorica and Iberia). In contrast, Eastern Laurentia, to the north of the WINB, was devoid of orogenic activity at this time. WINB samples also yield age populations younger than 500 Ma, and older than 700 Ma. These are not diagnostic of a particular source terrane and thus could be derived from terranes north and/or south of the WINB. WINB detrital zircon age spectra can be reconciled by an Avalonian or combined Avalonian–Laurentian provenance for WINB sedimentary strata. Further research is required in order to distinguish between these two possibilities. Copyright © 2011 John Wiley & Sons, Ltd.

Uranium deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in uranium oxides, for a series of worldwide uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first-order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of uranium deposits and for genetically discriminating new uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking.

"Laser ablation inductively coupled plasma mass spectrometry was used to analyze the
individual chambers from tests of foraminiferal fossil and plankton tow Globigerinoides
ruber from the southwest Pacific Ocean, from latitudes 3°S to 42°S. The variability of
Mg/Ca between chambers of an individual (intraindividual) and individuals of the same
population (interindividual), is such that when converted to temperature, the extent of
intra‐individual and interindividual variability appears to exceed that attributable to either
calcification or seasonal temperature variability. The pooled mean chamber Mg/Ca
from each core top and plankton tow site demonstrates a significant (p < 0.05) positive
correlation with temperature. We derive chamber‐specific calibrations where Mg/CaCh_F‐2 =
0.798 exp0.070 T, Mg/CaCh_F‐1 = 0.891 exp0.067 T and Mg/CaCh_F = 0.590 exp0.072 T.
We do not observe any bias between the two morphotypes Gs. ruber ruber and Gs. ruber
pyramidalis. The chamber‐specific calibrations potentially offset Mg/Ca‐based temperature
reconstructions if used on bulk (whole) test Mg/Ca or applied to misidentified chambers.
Nevertheless, these calibrations can be used to reliably estimate sea surface temperature.
Although there is a general overriding temperature control on Mg/Ca, we show that removal
of the effect of temperature at each site reveals a lognormal Mg/Ca distribution. This
suggests that Mg/Ca variability at each site is also affected by biological mechanism(s)
that may control the distribution of interindividual Mg/Ca. In addition, other TE/Ca data
(Al/Ca and Mn/Ca) from laser ablation trace element depth profiles can be used to identify
detrital or diagenetic phases that may bias the trace element/Ca signal."

Laser ablation coupled to a multi-collector inductively coupled mass spectrometer (LA-MC-ICP-MS) is a promising tool for in situ analysis of metal and metalloid stable isotope ratios. Potential isotopic fractionation associated with laser ablation may, however, cause biased sampling of the substrate, posing a major challenge for precise and accurate isotope ratio measurements. To better characterize the nature of laser ablation induced isotopic fractionation, this study compared particle morphologies, sizes, and size-dependent Fe isotope fractionations produced by ablation of a suite of semi-conductive samples, including natural Fe oxide, sulfide, and carbonate minerals, under various conditions using a 193 nm ArF nanosecond (ns) laser and a 266 nm Ti:sapphire femto-second (fs) laser. Ablation-produced particles were sorted based on aerodynamic size using a cascade impactor, and Fe isotope compositions of size-sorted particles were then measured offline using conventional solution neb-ulization ICP-MS to quantify isotopic fractionation produced by the laser ablation. Particle morphology and size distributions produced by ns-laser ablation are more substrate and fluence dependent as compared to fs-laser ab-lation, resulting from the thermal nature of ns-laser ablation. Often, a higher proportion of the ablated Fe mass resides in particles with large aerodynamic sizes during ns-laser ablation as compared to fs-laser ablation, posing a potential difficulty for LA-ICP-MS analysis due to the increased possibility of incomplete ionization of large particles. Significant size-dependent Fe isotope fractionations of up to several per mil can occur during both ns-and fs-laser ablation, highlighting the importance of quantitative transport of particles to the ICP-MS for accurate Fe isotope analysis. Size-dependent Fe isotope fractionation observed for fs-laser ablation of all Fe minerals can be explained by particle formation through a condensation model, but multiple processes need to be considered to explain the observed Fe isotope fractionation during ns-laser ablation. Mass-balance calculations suggest that ns-laser ablation does not sample magnetite stoichiometrically for Fe isotope compositions at low fluence (1 J/cm 2), but does at higher fluences for all minerals. In contrast, fs-laser ablation always provides stoichiometric sampling for Fe isotopes regardless of fluence. Results of this study demonstrate that ns-laser ablation is sub-strate-and fluence-dependent, resulting in variable particle size distributions and Fe isotope fractionations, and possible non-stoichiometric sampling of semi-conductive samples for Fe isotope analysis. Instead, fs-laser ablation largely minimizes the substrate and fluence dependence, providing more consistent ablation.

Laser ablation inductively coupled plasma mass spectrometry was used to analyze the individual chambers from tests of foraminiferal fossil and plankton tow Globigerinoides ruber from the southwest Pacific Ocean, from latitudes 3° S to 42° S. The variability of Mg/Ca between chambers of an individual (intraindividual) and individuals of the same population (interindividual), is such that when converted to temperature, the extent of intra-individual and interindividual variability appears to exceed that attributable to either calcification or ...

The processes by which Athenian black- and red-figure vases were produced appear to be well understood, with text-books regularly offering succinct descriptions of levigation, the application of relief line, and the three-stage firing process. A number of aspects, however, remain hypothetical, and new analytical techniques can inform old questions. In 2011, with funding from the National Science Foundation, the Getty Conservation Institute and J. Paul Getty Museum undertook a project to characterize Athenian black gloss. By partnering with The Aerospace Corporation, the Stanford Synchrotron Radiation Lightsource (SSRL), and The Northwestern University/Art Institute of Chicago Center for Scientific Studies in the Arts (NU-ACCESS), we created a team which had a diverse range of interests and equipment, with a view to obtaining new and rigorously-tested data. Combining these analyses with replication studies, we documented the ways in which black gloss responded during firing. Some of the results have been published in scientific journals, but in order to share them more broadly, we present here a summary of three case-studies. Taken together, they indicate that the production of the vases may be more complex than
the conventional notion of a single three-stage firing process (oxidation-reduction-oxidation) suggests.