Bence Paul

Iolite: Freeware for the visualisation and processing of mass spectrometric data

Iolite is a non-commercial software package developed to aid in the processing of inorganic mass spectrometric data, with a strong emphasis on visualisation versus time of acquisition. The goal of the software is to provide a powerful framework for data processing and interpretation, while giving users the ability to implement their own data reduction protocols. It is intended to be highly interactive, providing the user with a complete overview of the data at all stages of processing, and allowing the freedom to change parameters and reprocess data at any point. The program presents a variety of windows for the selection and viewing of data versus time, as well as features for the generation of X-Y plots, summary reports and export of data. In addition, it is capable of generating X-Y images from laser ablation rasters, and combining information from up to four separate elemental concentrations (intensities of red, green and blue, and the z-axis) in a false-colour three-dimensional image. By virtue of its underlying computing environment—Igor Pro—Iolite is capable of processing very large datasets (i.e., millions of timeslices) rapidly, and is thus ideal for the interrogation of multi-hour sessions of laser ablation data that can not be easily manipulated in conventional spreadsheet applications, for example. It is also well suited to multi-day sessions of solution-mode inductively-coupled plasma mass spectrometer (ICPMS) or thermal ionisation mass spectrometer (TIMS) data. A strong emphasis is placed on the interpolation of parameters that vary with time by a variety of user selectable methods including smoothed cubic splines. Data are processed on a timeslice-by-timeslice basis, allowing outlier rejection and calculation of statistics to be employed directly on calculated results. This approach can reduce the risk of processing biases associated with the manipulation of integrated datasets, while also allowing the implementation of more complex data reduction methods.

Improved in situ isotope analysis of low-Pb materials using LA-MC-ICP-MS with parallel ion counter and Faraday detection

A new analytical protocol is described allowing the measurement of Pb-isotope ratios, including the low abundance isotope 204Pb, in relatively small targets (∼100 micron) of low Pb content (1–10 ppm), such as might be encountered in the analysis of magmatic melt inclusions, for example. The analysis routine employed utilises multiple Faraday cups and two ion counters operated in static multi-collection mode. Concurrent analysis of the NIST 612 glass standard allows an external correction for mass bias, and simultaneous determination of ion counter gain, while Hg interference on 204Pb is corrected in real time by simultaneous acquisition of 200Hg in a second ion counter. Analytical precision approximates theoretical limits and it can be shown that analytical accuracy is limited primarily by ion counter gain for ratios involving 204Pb and the mass bias correction for all other ratios. We typically obtain precisions of <0.4% RSD (2 sigma) and accuracy of ≤0.2% on BCR2-g for ratios involving 204Pb. Two other glass reference materials (MPI-DING ATHO-G and KL2-G) were also analysed, and precision of ≤1.8% RSD (2 sigma) and accuracy of ≤0.9% were obtained for the glass with the lowest Pb abundance of approximately 2 μg g−1. These results provide an improvement on the accuracy and precision of laser ablation ratio determinations, attributable to stable instrument conditions and high sensitivity.

CellSpace: A module for creating spatially registered laser ablation images within the Iolite freeware environment

We present a novel approach to creating compositional images using a module created for use with the freely distributed software package Iolite. The module creates images by synchronising the state of the laser (e.g., whether the laser is firing or not) and the position on the sample, which are recorded in laser log files, with concurrently collected mass spectrometer data. When these two data sources are synchronised, mass spectrometer data which are recorded temporally can then be displayed versus ablation position (i.e., spatially). Each mass spectrometer reading is then plotted as a circular spot representing the size of the area ablated. This approach has many advantages. CellSpace takes advantage of Iolites ability to manipulate data from various mass spectrometers and to reduce data of different types. Laser ablation data can be plotted over other images, such as those produced by scanning electron microscopes, where the image has been transformed into cell coordinates using third party software. This allows the analyst to visualise laser ablation data in context and to correlate sample data from multiple sources and/or techniques. The code also has the advantage of averaging data spatially, rather than just temporally, and faithfully presents the data as a corresponding laser spot, rather than a simple rectangular pixel. Here we provide an example of a fish otolith, where trace element concentrations and Sr-isotopic compositions are overlain on microscope images, providing information on migration patterns that are applicable to population studies and fisheries conservation.

O-Hf isotope constraints on the origin of zircon in high-pressure melange blocks and associated matrix rocks from Tinos and Syros, Greece

Most previously dated zircons in high-pressure melange blocks and associated matrix rocks from Tinos and Syros (Cyclades), Greece, yielded ion microprobe (SHRIMP II) U-Pb ages of ca. 80 Ma. In many cases it remains unclear whether the zircons are igneous or metamorphic/hydrothermal in origin. Oxygen and hafnium isotope ratios in the dated zircons have been determined to further constrain their mode of formation. Spot analysis of zircons from metagabbro, eclogite, glaucophanite, jadeitite and chlorite schists by ion microprobe (CAMECA IMS-1280) yields a large range in δ 18 O, varying from 2.0 ‰ to 7.6 ‰ VSMOW. The average δ 18 O values for most zircons in 11 samples however fall within a relatively small compositional range between 4.7 ‰ and 5.5 ‰, which is consistent with an igneous origin. These values suggest a relationship to magmas typical for modern oceanic crust or to precursors that had been in equilibrium with primitive magma compositions or the mantle (5.3 ± 0.6 ‰, 2 SD). The δ 18 O (mantle-like) and initial epsilon hafnium values [ɛ Hf ( t ) = +10 to +24] suggest that the 80 Ma old zircons are igneous in origin and crystallised from magmas that were derived from depleted mantle. Scanning Electron Microscope cathodoluminescence imaging indicates that lower-δ 18 O zircons (grains or domains; down to 2.0 ‰), mostly from one exceptional eclogite sample (average 4.3 ± 0.8 ‰, 2 SD, n = 23), either represent cauliflower-like internal structures or weakly zoned (or porous) features in outer rims. Previous age dating of zircon domains with cauliflower-like internal structures indicated apparent ages that are considerably younger ( ca. 54 Ma and ca. 57 Ma) than the Cretaceous age determined for the majority of the zircon population. Taken together, these observations suggest that the low-δ 18 O zircons (and three high-δ 18 O zircons, > 6.0 ‰) are genetically linked to a well-documented Eocene high-pressure metamorphic event ( ca . 53–40 Ma), but post-magmatic seafloor hydrothermal alteration cannot be completely ruled out.

Mantle heterogeneity beneath the Cenozoic volcanic provinces of central Victoria inferred from trace-element and Sr, Nd, Pb and Hf isotope data

Volcanic rocks in central Victoria play a key role in unravelling magmatic relationships within an extensive zone of Late Mesozoic to Quaternary volcanism in southeastern Australia. In this study, new bulk-rock major, trace-element and Sr, Nd, Hf and Pb isotope data are presented for 20 samples of Late Cenozoic mafic volcanics from the central Victorian region. Mineral chemistry and bulk-rock analyses confirm that all samples can be treated as liquid compositions and that some were probably primary magmas. On the basis of incompatible trace-element and isotope ratios, processes such as magma mixing and crustal assimilation can be largely ruled out, and significant mantle-source heterogeneity beneath the area is proposed. If this heterogeneity extends to other regions of the post-10 Ma Victorian volcanics, the influence of the Mortlake Discontinuity and level of involvement from the lithospheric mantle in the genesis of these rocks, may need to be re-evaluated. Finally, it is argued that there is no clear evidence to suggest the New South Wales leucitite suite extends into Victoria; rather the Cosgrove leucitite flow represents part of the post-10 Ma Victorian volcanics.

Thermotectonic history of SE China since the Late Mesozoic: insights from detailed thermochronological studies of Hong Kong

The late Mesozoic Yanshanian volcanic arc affected an extensive region of SE China, but the conclusion of magmatism and later evolution are not fully understood. Widespread Yanshanian ignimbrites and their contemporaneous granites exposed in Hong Kong represent a microcosm of this magmatic arc. To constrain the post-magmatic thermal history of the region, we present zircon and apatite fission-track analyses from these rocks. Double dating using laser ablation inductively coupled plasma mass spectrometry U–Pb and fission-track techniques on detrital zircons from post-volcanic Cretaceous sediments is used to further constrain the tectonothermal evolution. The resulting dataset and thermal modelling suggest that the igneous rocks and Cretaceous sediments together experienced post-emplacement or post-depositional heating to >250 °C, subsequently cooling through 120–60 °C after c. 80 Ma. The heating reflects the combined effects of an enhanced geothermal gradient and burial. We interpret the enhanced gradient to represent continuing Yanshanian magmatic activity until c. 100–80 Ma, much later than previously considered. Our data also indicate a long-term, slow cooling (c. 1 °C myr–1) since the early Cenozoic, linked to c. 2–3 km of erosion-driven exhumation. The thermotectonic history of Hong Kong reflects the mid-Cretaceous transition of SE China from an active to a passive margin bordered by marginal basins that formed in the early Cenozoic. Supplementary material: Descriptions of samples, operating conditions of the laser ablation inductively coupled plasma mass spectrometry system and the full dataset of U–Pb dating of detrital zircons are available at www.geolsoc.org.uk/SUP18750.

Imaging Metals in Brain Tissue by Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS)

Metals are found ubiquitously throughout an organism, with their biological role dictated by both their chemical reactivity and abundance within a specific anatomical region. Within the brain, metals have a highly compartmentalized distribution, depending on the primary function they play within the central nervous system. Imaging the spatial distribution of metals has provided unique insight into the biochemical architecture of the brain, allowing direct correlation between neuroanatomical regions and their known function with regard to metal-dependent processes. In addition, several age-related neurological disorders feature disrupted metal homeostasis, which is often confined to small regions of the brain that are otherwise difficult to analyze. Here, we describe a comprehensive method for quantitatively imaging metals in the mouse brain, using laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) and specially designed image processing software. Focusing on iron, copper and zinc, which are three of the most abundant and disease-relevant metals within the brain, we describe the essential steps in sample preparation, analysis, quantitative measurements and image processing to produce maps of metal distribution within the low micrometer resolution range. This technique, applicable to any cut tissue section, is capable of demonstrating the highly variable distribution of metals within an organ or system, and can be used to identify changes in metal homeostasis and absolute levels within fine anatomical structures.

Characterisation of matrix-based polyatomic interference formation in laser ablation-inductively coupled plasma-mass spectrometry using dried micro-droplet ablation and its relevance for bioimaging

Dried micro-droplets were used to characterise the formation of polyatomic interferences in a commercial laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS). Droplets containing 4 ng each of Al, As, Ca, Cd, Co, Cu, Fe, Mg, Mn, P, Se and Zn in the presence of potentially interfering isotopes were deposited on silicate microscope slides. Comparisons of the total signal recorded for each dried droplet showed no detectable influence of polyatomic matrix-based interferences. Visualisation of acquired signal was achieved by the generation of two-dimensional maps. The natural abundance pattern of elements with two measurable isotopes was confirmed for each droplet. The lack of interferences was due to the absence of major gas molecules (e.g. N2, O2, CO2) from the laser cell and minimal total matrix load on the plasma when compared to standard solution nebulisation (approx. ng s−1versus 10–20 μL s−1) ICP-MS conditions.

A model for the formation of layered soda-straw stalactites

*bpaul@unimelb.edu.au, jdwood@unimelb.edu.au and disadvantages. For example, tree-ring records in Australia are limited to species growing in only a few specific ecological environments (Pearson & Searson, 2002). Additionally, some proxies are not necessarily located near large population centres, which are key to future water-use and infrastructure policy planning. One well-established source of climate proxy information is speleothem calcite. Speleothems have the advantage of being widely distributed geographically and thus allow us to reconstruct local palaeoclimate conditions at many sites. In addition, they appear to be sensitive to both temperature and rainfall (Proctor et al., 2002; Johnson et al., 2006) and are ideally suited to radiometric dating via U-Th and U-Pb protocols. This has led to their widespread applicability to address a variety of palaeoclimate problems (Mariethoz et al., 2012). In general, however, INTRODUCTION