ALBERT

Description: Since december 2013 the Helmholtz Zentrum Potsdam has operated a 1280-HR instrument: the latest generation of Cameca large geometry ion microprobe. Here we report the observed performance of this tool, with particular emphasis on the determination of isotopic ratios on geomaterials. We have already acquired extensive experience in the determination of δ 18 o values in silicates, for which a single analysis requires circa 80 seconds of actual data acquisition. Running in full automatic mode and with the reference material(s) embedded within the grain mount, we are thus able to complete some 250 analyses in a 24 hour cycle. For such analyses we typically achieve an analytical repeatability of ± 0.15 ‰ (1sd), though we have recorded repeatabilities down to ± 0.092 ‰ (1sd, n = 100) in one suite of zircon analyses. a main consideration in δ 18 o analyses with the 1280-HR is the need for careful sample preparation: on samples with as little as 5 μm topographic relief between silicate grains and epoxy embedding media we have observed charging problems despite using both a 35 nm gold coating and 〉 1 μA of low energy electron flooding. Thanks to the availability of a well characterized suite of tourmaline rMs, boron isotope analyses are already a well established application in the potsdam SIMS facility. Here a single analysis involves 80 s of data acquisition, from which we can obtain a typical repeatability of ± 0.25 ‰ (1sd) and an overall analytical uncertainty of ± 0.9 ‰ based on a suite of four distinct tourmaline rMs. We have also been able to analyze the boron isotopic compositions on areas as small as 3 μm with only a modest reduction in overall precision. Large demand exists for U-Th-Pb age determinations, for which we currently have rMs only for zircon. For such work a single analysis commonly requires 12 to 15 minutes of data acquisition, meaning that a complete project typically involves circa 5 days of laboratory usage. Our zircon U-Pb protocol calls for the analysis of a quality control material during all analytical sessions. Here we often observe a ~1 % bias in the Pb/U results from the QCM as calibrated by the primary reference material. We conclude that under normal circumstances our inter-element results are reliable at the ± 2 ‰ level. A key feature of the 1280-HR tool is the ability to conduct oxygen flooding during the analyses, which results in a 2x improvement in instrument sensitivity for pb data acquisition. mThe technology behind the 1280-HR is sufficiently mature such that the main factor limiting analytical quality has, at least in some isotopic systems, become the interlaboratory bias observed during the “bulk” characterization of the reference materials. A key limiting factor in the performance of the instrument itself is the constraint that only a single, 1-inch diameter sample may be in the secondary ion source at a time. This limitation often compels frequent sample exchanges in order to access calibration materials, thereby prohibiting extended automated runs.

Description: Here we report on a set of six apatite reference materials (chlorapatites MGMH# 133648, TUBAF# 38 and fluorapatites MGMH# 128441A, TUBAF# 37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with 〉 0.5% m/m Cl, and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.

Description: Thanks to its extremely fine sampling size, Secondary Ion Mass Spectrometry (SIMS) is one of the most powerful methods available to the analytical geochemist. State-of-the-art SIMS instrumentation can determine precise isotope ratios at the 〈 200 pg scale and can provide high quality U-Pb data from e.g., zircons at total sampling masses under 5 ng. In late 2013 the Helmholtz Zentrum Potsdam completed installation of a Cameca 1280-HR instrument, which is to operate as an open user facility. This instrument is to server the global user community by providing access to top-quality SIMS infrastructure in as simple and uncomplicated means as possible. The Potsdam 1280-HR instrument is equipped with a five trolley multi-collection ion detection system that enables isotope ratio determinations (e.g., δ11B, δ18O, δ34S) with repeatabilities at or below ± 0.2 ‰ (1sd) on major elements. We can equip the multi-collector with both electron multipliers or Faraday cups, and the system is flexible permitting both types of two ion detection methods to be combined, as is best optimize for a given application. During a typical 24 hour operating cycles between 250 and 35 analyses can be produced. Other applications such as U-Pb geochronology, depth profiling and the quantification of volatile element cycles will also be major research themes in the Potsdam facility. We also have a major focus on the precaution of a new suite of reference materials for calibrating both SIMS and other microanalytical methods, and here we benefit from a large consortium of interested universities and research facilities within the Berlin/Potsdam region. Along side our SIMS tool we are also supported by an extensive range of peripheral instrumentation. This includes a fully motorized optical microscope for sample documentation, a white light optical profilometer for determining crater dimensions at the sub-micron scale and a polychromatic cathode luminescence chamber. Additionally, the GFZ can provide access to a complete sample preparation facility along with other large instruments such as a field emission (FE) scanning electron microscope for backscattered electron and monochromatic CL imaging, a FE electron microprobe for major element determinations, a dual-beam FIB instrument and a Raman spectrometer. During the planning of the Potsdam SIMS facility detailed consideration was given to the design of our laboratory space. Our 1280-HR is housed in a room which has 2 autonomous air handling systems. Temperature within the majority of the room is dynamically controlled to maintain an air temperature stability within a 0.5 C° range, regardless of variations in heat load into the laboratory. Air supply is provided from below floor level and the heat is extracted at ceiling level. The air in the room is completely exchanged every 2 minutes with relative humidity maintained at below 72 % relative. In order to further assure the maximum stability of the instrument there is a second, independent air supply operating at a constant temperature and flow rate which delivers air to the main electronics rack from beneath floor level. The electronics rack has its own heat extraction hood to extract the thermal output immediately from the laboratory. The Cameca 1280-HR can operate autonomously for up to 45 minutes using an uninterruptable power supply, which also acts as a line conditioner. In order to fully minimize disturbances to laboratory environment the actual machine operation is conducted from an adjoining office. All superfluous heat sources, such as a vacuum-capable drying oven and sample coater, have been removed to a dedicated sample preparation room, which also adjoins the SIMS laboratory. We have already completed a number of projects, and here we will show some of the performance capabilities of our instrument.

Description: The solubility of N2 in basaltic (MORB) and haplogranitic melts was studied at oxidizing conditions (oxygen fugacity about two log units above the Ni–NiO buffer). Under these conditions, N2 is expected to be the only significant nitrogen species present in the melt. Experiments were carried out from 0.1 to 2 GPa and 1000–1450 ˚C using either an externally heated TZM pressure vessel, an internally heated gas pressure vessel or a piston cylinder apparatus. Nitrogen contents in run product glasses were quantified by SIMS (secondary ion mass spectrometry). To discriminate against atmospheric contamination, 15N-enriched AgN3 was used as the nitrogen source in the experiments. According to infrared and Raman spectra, run product glasses contain N2 as their only dissolved nitrogen species. Due to interactions with the matrix, the N2 molecule becomes slightly infrared active. Nitrogen solubility in the melts increases linearly with pressure over the entire range studied; the effect of temperature on solubility is small. The data may, therefore, be described by simple Henry constants Khaplogranite = (1461 ± 26) ppm N2/GPa and KMORB = (449 ± 21) ppm N2/GPa, recalculated to ppm by weight (μg/g) of isotopically normal samples. These equations describe the solubility of nitrogen during MORB generation and during melting in the crust, as we show by thermodynamic analysis that N2 is the only significant nitrogen species in these environments. Nitrogen solubility in the haplogranitic melt is about three times larger than for the MORB melt, as is expected from ionic porosity considerations. If expressed on a molar basis, nitrogen solubility is significantly lower than argon solubility, in accordance with the larger size of the N2 molecule. Notably, N2 solubility in felsic melts is also much lower than CO2 solubility, even on a molar basis. This implies that the exsolution of nitrogen may drive vapor oversaturation in felsic melts derived from nitrogen-rich sediments. We also measured the partitioning of nitrogen between olivine, pyroxenes, plagioclase, garnet, and basaltic melt by slowly cooling MORB melts to sub-liquidus temperatures to grow large crystals. The mineral/melt partition coefficients of nitrogen range from 0.001 to 0.002, and are similar to argon partition coefficients. These new data, therefore, support the assumption that there is little fractionation between nitrogen and argon during mantle melting and that the N2/Ar ratio in basalts and xenoliths is, therefore, representative of the N2/Ar ratio in the mantle source. This assumption is essential for assessing the size of the nitrogen reservoir in the mantle. Our data also show that for an upper mantle oxidation state that is similar to the one observed today, nitrogen outgassing by partial melting is extremely efficient and even low melt fractions in the range of a few percent may extract nearly all nitrogen from the mantle source.

Description: The Raman spectra of five [4]B-bearing tourmalines of different composition synthesized at 700°C/4.0 GPa (including first-time synthesis of Na-Li-[4]B-tourmaline, Ca-Li- [4]B-tourmaline and Ca-bearing -[4]B-tourmaline), reveal a strong correlation between the tetrahedral boron content and the summed relative intensity of all OH-stretching bands between 3300–3430 cm-1. The band shift to low wavenumbers is explained by strong O3-H...O5 hydrogen bridge bonding. Applying the regression equation to natural [4]B-bearing tourmaline from the Koralpe (Austria) reproduces the EMPA-derived value perfectly [EMPA: 0.67(12) [4]B pfu vs. Raman: 0.66(13)[4]B pfu]. This demonstrates that Raman spectroscopy provides a fast and easy-to-use tool for the quantification of tetrahedral boron in tourmaline. The knowledge of the amount of tetrahedral boron in tourmaline has important implications for the better understanding and modeling of B-isotope fractionation between tourmaline and fluid/melt, widely used as tracer of mass transfer processes.

Description: A CAMECA 1280-HR SIMS (secondary ion mass spectrometer) was installed at the Deutsches GeoForschungsZentrum Potsdam / Helmholtz Zentrum Potsdam in November 2013. The new ion microprobe laboratory functions as an open user facility, in accordance with the Helmholtz Society's support of the scientific community through providing access to top-end infrastructure. The 1280-HR instrument will be integrated into the Helmholtz SIMS network, whereby the activities in the Potsdam laboratory will be closely coordinated with new SIMS infrastructure currently being installed in both Dresden (accelerator SIMS using a CAMECA 7f as its ion source) and Leipzig (NanoSIMS 50L). The Potsdam 1280-HR is intended mainly for geoscientific studies, however, the facility will also support a limited number of well defined material science investigations as well as serving as a platform for instrumentation development work. The state-of-the-art, ultra-high sensitivity and large geometry instrument consists of the basic 1280-HR design, including the five trolley multi-collection system along with a Resistive Anode Encoder, thus making the system optimized for both low-uncertainty isotope ratio determinations (e.g., δ 13 C, δ 18 O and δ 34 S) as well as quantification and distribution mapping of low concentration elements in minerals, glasses or biological materials. The possibility of very high mass resolution of M/dM ≥ 30,000 will also allow the separation of isobaric masses, such as 40 Ca and 40 K. Envisioned key research topics include H, B, C, O, S and Pb isotopic studies, geochronology applications and the quantificaiton of volitile elements in geological materials. Although our SIMS team is still gaining initial experience with this new technology, we have already completed out several isotope, solubility and diffusion studies. This contribution provides a brief overview on the current state of the Potsdam SIMS facility, its analytical progress and present operational capabilities. We invite the community to take advantage of this geochemical tool.