Paul R.D. Mason

MPI‐DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

A critical assessment of laser ablation ICP-MS as an analytical tool for depth analysis in silica-based glass samples

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a versatile technique for trace element analysis with respect to depth in solid samples. The high sensitivity of ICP-MS makes it possible to determine most elements in the periodic table at trace levels (<1 µg g –1 ). Recent trends in the development of instrumentation have led to the possibility of analysing craters of smaller diameter with variable depth. However, a major limitation to this approach for depth profiling, preventing accurate and precise analysis, is element-selective, non-reproducible ablation. The ability for representative sampling during depth analysis is tested in this study by ablating into homogeneous silica-based glass materials. Elemental relative response deviations of up to 300% are observed for selected elements during progressive ablation into the glass target. The geometry of the ablation crater controls the accuracy of sampling of the material at depth. Elemental fractionation becomes significant for some elements (e.g., Zn, Pb) when the depth/diameter ratio of the ablation crater is >6, corresponding to a 50% reduction in analyte response. Large diameter craters, if ablated with sufficient laser power density, reduce elemental fractionation and give a larger signal for a longer period of time, providing more suitable conditions for representative analysis. LA-ICP-MS can be a powerful technique for depth profiling provided that optimum analytical conditions are selected.

Single foraminiferal test chemistry records the marine environment

We applied laser-ablation inductively coupled plasma‐mass spectrometry (LA-ICP-MS) as a new and precise technique for measuring trace elements in benthic foraminifera (Hoeglundina elegans). With this technique, trace element concentrations were accurately measured without the elaborate cleaning required in standard methods. Contaminated coatings are easily excluded during spatially resolved analysis. Application of this new technique allowed us to calibrate the trace elements incorporated in single tests of living (when sampled) benthic foraminifera to ambient seawater temperature (Mg and Sr) and redox conditions (Mn) for the first time. Incorporation of Ba showed a more complex pattern that cannot be explained by a direct correlation to water column concentration.

Deep origin and hot melting of an Archaean orogenic peridotite massif in Norway

The buoyancy and strength of sub-continental lithospheric mantle is thought to protect the oldest continental crust (cratons) from destruction by plate tectonic processes. The exact origin of the lithosphere below cratons is controversial, but seems clearly to be a residue remaining after the extraction of large amounts of melt. Models to explain highly melt-depleted but garnet-bearing rock compositions require multi-stage processes with garnet and clinopyroxene possibly of secondary origin. Here we report on orogenic peridotites (fragments of cratonic mantle incorporated into the crust during continent-continent plate collision) from Otrøy, western Norway. We show that the peridotites underwent extensive melting during upwelling from depths of 350 kilometres or more, forming a garnet-bearing cratonic root in a single melting event. These peridotites appear to be the residue after Archaean aluminium depleted komatiite magmatism.

Sulfur and chalcophile elements in subduction zones: constraints from a laser ablation ICP-MS study of melt inclusions from Galunggung Volcano, Indonesia

Abstract Mafic melt inclusions hosted in olivine phenocrysts (Fo89–78) in high-Mg basalts of Galunggung volcano (Java, Indonesia) were analyzed in situ by laser ablation ICP-MS to determine concentrations of chalcophile and associated trace elements. Our results indicate that sulfur in the mantle beneath Galunggung is significantly enriched relative to MORB source mantle, suggesting large-scale fluxing of sulfur into the mantle wedge during slab dehydration. Melt-inclusion compositions range from strongly undersaturated to transitional basaltic and are characterized by a wide range of sulfur contents (350–2900 ppm). Chalcophile element concentrations are not affected by exsolution of immiscible sulfide liquids and generally fall within the range of whole-rock samples from other arcs. We infer that primary Galunggung melts contain approximately 290 ppm Ni, 60 ppm Co, 190 ppm Cu, and 3 ppm Pb. Patterns of refractory trace elements point to ∼15% melting of a MORB-source mantle below Galunggung, which was enriched in LILE and LREE by slab-derived fluids before melting. Based on this value, we use melting model calculations to investigate whether slab-derived contributions to a MORB-source mantle are required to balance the budgets of sulfur and associated chalcophile elements, assuming that all Cu and S originally resided in sulfides and adopting a Cu concentration of 28 ppm in the presubduction mantle, similar to that in MORB-type mantle. Modeling results predict at least 256 to 465 ppm S in the magma source of Galunggung, which is up to twice the amount commonly assumed for MORB sources. A slab-derived origin of the excess sulfur is consistent with 34S enrichments that commonly characterize arc magmas and gases. Although modeling suggests that elevated copper concentrations relative to MORB can be the consequence of the higher solubility of sulfur in Galunggung melts, the results do not rule out that the subarc mantle was enriched by slab-derived Cu. Lead must have been added, which is readily explained by slab-derived fluids. Other chalcophile elements (Co, Ni) are largely controlled by the nature of the presubduction mantle.

Magmatic constraints on geodynamic models of subduction in the East Carpathians, Romania

Abstract The East Carpathian volcanic arc is the youngest region of calc-alkaline magmatic activity in Eastern Europe. A general age progression of the onset and cessation of magmatic activity occurs along the East Carpathian arc from older volcanic structures (ca. 12 Ma) in the NW to the youngest (

Determination of sulfur isotope ratios and concentrations in water samples using ICP-MS incorporating hexapole ion optics

Sulfur isotope ratios are difficult to determine by quadrupole ICP-MS due to interfering O 2 + and NO + molecular ions of high signal intensity at isotopes 32 S and 34 S. Rf-only hexapole devices have recently been introduced into ICP-MS instrumentation to facilitate ion transfer from interface to analyser. By introducing a mixture of ‘reactive’ gases into the hexapole, a series of ion-molecule reactions can be induced to reduce or remove interfering polyatomic species. The effects of various gas mixtures (He, H 2 and Xe) on the transfer of sulfur ions through the hexapole and the breakdown of interfering O 2 + and NO + molecular ions at m/z=32 and m/z=34 were investigated. A rapid charge transfer reaction between O 2 + and Xe gives at least a factor of 10 improvement in the S + /O 2 + ratio. A further reduction in O 2 + is achieved by the addition of H 2 . δ 34 S variations were investigated in crater-lake waters and waters obtained from springs and rivers on the flanks of volcanoes in Java, Indonesia. Under optimum conditions (S=10-50 mg l –1 ), the 34 S/ 32 S measurement precision for standards and samples was <0.3% RSD. Mass bias errors were corrected by using a concentration-matched in-house standard of average North Atlantic sea-water (δ 34 S=20.5). Results compare favorably against published data measured by standard gas source mass spectrometric techniques. The proposed technique is potentially useful as a survey tool due to the large δ 34 S variation (±20) encountered in nature and the accuracy and reproducibility of the technique (±3-5).

Mantle domains in the lithosphere beneath the French Massif Central: trace element and isotopic evidence from mantle clinopyroxenes

Lenoir et al. [Earth Planet. Sci. Lett. 181 (2000) 359] have suggested the existence of a lithospheric domain boundary at approximately 45°30′N within the French Massif Central because of differences in bulk rock geochemistry between mantle peridotite xenoliths from localities north and south of this latitude. New laser ablation ICP–MS analyses of trace element contents in clinopyroxenes from xenoliths from the northern domain, combined with Sr and Nd isotopic data for the same clinopyroxenes, clearly indicate significant differences between the northern and southern domains. LA–ICP–MS results show that the northern domain peridotites have experienced significantly more depletion than ones from the southern domain, having undergone almost twice as much fractional melting. Although they do not contain garnet at the present day, the northern domain peridotites appear to have contained garnet when they underwent melting. They can have extremely high Sm/Nd ratios (>0.5), indicating unusually strong depletion in Nd relative to Sm. However, they are also more enriched in LREE and Sr, and show significant fractionation of Zr from Hf, and of U from Th (Zr/Hf and Th/U≪chondritic values). This is due to metasomatism, possibly related to carbonitite infiltration. The Sr–Nd isotopic compositions of northern domain xenoliths are also unusual, in that many have high 143Nd/144Nd or high 87Sr/86Sr values which do not occur in samples from the southern domain. In contrast, the southern domain mantle shows low (MORB source) 87Sr/86Sr values not found in the northern domain. This confirms that significant differences exist between the two domains and offers strong support to the concept of the existence of lithospheric blocks with separate histories beneath the Massif Central. A remarkable similarity exists between the mantle beneath the northern domain of the Massif Central and that beneath the Rhon volcanic area (Germany) 1000 km to the northeast.

Late Neoproterozoic proto-arc ocean crust in the Dariv Range, Western Mongolia: a supra-subduction zone end-member ophiolite

An unusual late Neoproterozoic (c. 572 Ma) ophiolite is exposed in the Dariv Range (western Mongolia), which contains intermediate to acidic lavas and sheeted dykes, and an igneous layered complex consisting of gabbro–norites, websterites, orthopyroxenites and dunites underlain by serpentinized mantle harzburgites. Based on the compositions of the crustal units and the crystallization sequences in the mafic and ultramafic cumulates we conclude that the entire oceanic crust, including the cumulates, was made from arc magmas with boninitic characteristics. The Dariv rocks bear a strong resemblance to rocks recovered from the modern Izu–Bonin–Mariana fore-arc, a fragment of proto-arc oceanic basement, and we propose that the Dariv Ophiolite originated in a similar tectonic setting. A metamorphic complex consisting of amphibolite- to granulite-facies metasedimentary and meta-igneous rocks was thrust over the ophiolite. This metamorphic complex probably represents a Cambrian arc. Thrusting started before 514.7 ± 7.6 Ma as constrained by new sensitive high-resolution ion microprobe U–Pb zircon analyses from a syn- to post-tectonic diorite. The Dariv Ophiolite is a type-example of a proto-arc ophiolite, a special class of supra-subduction zone ophiolites.

In situ determination of sulfur isotopes in sulfur-rich materials by laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)

A new method has been developed for the accurate and precise measurement of sulfur isotopes (32S, 33S, 34S) in solids on a scale down to 80–100 μm by laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The method was developed independently on two different sets of instrumentation, both of which give equivalent results with comparable accuracy and precision. The first instrumental set-up utilizes Xe gas in a hexapole collision and reaction cell for interference attenuation coupled with a mass discrimination correction by external normalization using a nebulised vapour of 37Cl/35Cl standard solution. The second employs high mass resolution by sector field mass spectrometry to avoid the interfering O2+ isobars with a 30Si/29Si standard aerosol for external normalization. The external isotope mass discrimination correction was applied using the exponential law and was further calibrated for both sets of instrumentation by linear interpolation in a sample–standard bracketing method. Mean δ34SV-CDT and δ33SV-CDT show excellent agreement (within analytical error, typically 0.6 and 1.5‰, respectively) with compiled data for IAEA-S series AgS standard reference materials. Results for NIST SRM 127 (sulfate) were less accurate when calibrated against the IAEA-S series sulfides, whilst significant and consistent deviations in accuracy of up to 3‰ were observed in both sets of instrumentation for Soufre de Lacq SRM sulfur. Such generic matrix effects may be widespread in LA-ICP-MS due to differential ablation rates, particle formation, particle transport efficiency and ionization efficiency in an argon plasma.