Maurizio Petrelli

PetroGraph: A new software to visualize, model, and present geochemical data in igneous petrology

A new software, PetroGraph, has been developed to visualize, elaborate, and model geochemical data for igneous petrology purposes. The software is able to plot data on several different diagrams, including a large number of classification and “petrotectonic” plots. PetroGraph gives the opportunity to handle large geochemical data sets in a single program without the need of passing from one software to the other as usually happens in petrologic data handling. Along with these basic functions, PetroGraph contains a wide choice of modeling possibilities, from major element mass balance calculations to the most common partial melting and magma evolution models based on trace element and isotopic data. Results and graphs can be exported as vector graphics in publication-quality form, or they can be copied and pasted within the most common graphics programs for further modifications. All these features make PetroGraph one of the most complete software presently available for igneous petrology research.

Elemental Imaging and Petro-Volcanological Applications of an Improved Laser Ablation Inductively Coupled Quadrupole Plasma Mass Spectrometry

We report on the performance of the a new LA-ICP-MS instrumentation installed at the Physics and Geology Department of Perugia University empathizing its capabilities in elemental imaging and the progresses in trace element in situ determination and U/Pb geochronology. The analytical device consists in a Thermo Fisher Scientific iCAP Q quadrupole mass spectrometer coupled with a Teledyne/Photon Machine ArF Excimer G2 laser ablation system. Results show that, in trace element configuration at 40 micron, precisions are better than 6.5% whereas accuracies are better than 10%. Results also show improved precisions with respect the X7 + UP213 instrumentation in U/Pb geochronological studies. On this regard, concordia ages for the Plesovice and R33 Zircons analyzed as unknowns are in close agreement with the accepted values for these reference materials highlighting the accuracy of the method. The potentials in 2D element imaging are also reported and successfully tested on a zoned plagioclase from the alkali basaltic Santa Venera lava Flow. Results evidences that expanding the analysis to the second dimension will lead to more reliable and accurate results and it is going to open new prospective for the modeling of igneous systems.

Concentration variance decay during magma mixing: a volcanic chronometer.

The mixing of magmas is a common phenomenon in explosive eruptions. Concentration variance is a useful metric of this process and its decay (CVD) with time is an inevitable consequence during the progress of magma mixing. In order to calibrate this petrological/volcanological clock we have performed a time-series of high temperature experiments of magma mixing. The results of these experiments demonstrate that compositional variance decays exponentially with time. With this calibration the CVD rate (CVD-R) becomes a new geochronometer for the time lapse from initiation of mixing to eruption. The resultant novel technique is fully independent of the typically unknown advective history of mixing – a notorious uncertainty which plagues the application of many diffusional analyses of magmatic history. Using the calibrated CVD-R technique we have obtained mingling-to-eruption times for three explosive volcanic eruptions from Campi Flegrei (Italy) in the range of tens of minutes. These in turn imply ascent velocities of 5-8 meters per second. We anticipate the routine application of the CVD-R geochronometer to the eruptive products of active volcanoes in future in order to constrain typical “mixing to eruption” time lapses such that monitoring activities can be targeted at relevant timescales and signals during volcanic unrest.

Origin and evolution of the Pleistocene magmatism of Linosa Island (Sicily Channel, Italy)

Major, trace element and Sr-Nd isotope data are reported for volcanic rocks from Linosa Island (Sicily Channel) with the aim of discussing the genesis and evolution of magmatism at the northern margin of the African plate. The volcanic rocks exposed at Linosa exhibit a transitional to mildly Na-alkaline affinity and are mainly mafic in composition (alkali basalt to hawaiite); benmoreitic to trachytic lithic clasts occur in the lowest exposed pyroclastic deposits. Magmas have been erupted between 1.06 ± 0.10 and 0.53 ± 0.07 Ma during three main cycles of activity: Paleolinosa, Arena Bianca and Monte Bandiera. Major and trace element data indicate a magma evolution by dominant fractional crystallization. However, compatible vs. incompatible element diagrams highlight distinct variation trends, which are interpreted to suggest fractional crystallisation starting from slightly different parental magmas, and separation of distinct mineral assemblages during polybaric evolution. Small variation of Sr and Nd isotope ratios indicate modest interaction with the crust. As other mafic magmas in Eastern Sicily and Sicily Channel (Etna, Iblei, Pantelleria, Sicily Channel seamounts), the most primitive magmas at Linosa are characterised by enrichments in high-field-strength elements (Nb, Ta) and depletion in Rb, Cs and other large ion lithophile elements. Their isotopic signatures fall close to the field of the so-called EAR (European Asthenospheric Reservoir) and FOZO (Focus Zone) mantle compositions. However, there are many significant geochemical and isotopic differences among various volcanoes in Eastern Sicily and Sicily Channel, which suggest variable degrees of melting at different depths of a heterogeneous mantle source. Overall, radiogenic isotope signatures reflect mixtures between EAR-FOZO and DMM (Depleted MORB Mantle) and may be related to mixing of asthenosphere-lithosphere or to variably metasomatised lithospheric mantle.

High spatial resolution trace element determination of geological samples by laser ablation quadrupole plasma mass spectrometry: implications for glass analysis in volcanic products

Increasing the spatial resolution of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a challenge in microanalysis of geological samples. Smaller sizes for the laser beam will allow for (1) high resolution determination of trace element compositions, (2) accurate estimation of crystal/melt partition coefficients, (3) detailed characterization of diffusion profiles, and (4) analysis of fine volcanic glasses. Here, we report about the figures of merit for LA-ICP Quadrupole MS down to a spatial resolution of 5 μm. This study highlights the possibility to achieve suitable limits of detection, accuracy and precision for geological samples even at spatial resolutions of the order of 5 μm. At a beam size of 15 μm, precision (measured as one sigma) and accuracy (expressed as relative deviation from the reference value) are of the order of 10%. At a smaller beam size of 8 um, precision decreases to 15% for concentration above 1.7 μg g–1. As the beam size is decreased to ∼5 μm, precision declines to about 15% and 20% for concentrations above 10 μg g–1 using 42Ca and 29Si as internal standard, respectively. Accuracy is better or equal to 10% and 13% at beam sizes of 15 and 10 μm, respectively. When the spatial resolution is increased to 8 μm, accuracy remains better than 15% and 20% for 42Ca and 29Si as internal standard, respectively. We employed such high-resolution techniques to volcanic glasses in ash particles of the 2010 Eyjafjallajökull eruption. Our results are well consistent with the previously reported data obtained at lower spatial resolution, supporting the reliability of the method.

Determination of travertine provenance from ancient buildings using self-organizing maps and fuzzy logic

This work is focused on determining provenance of travertine stones employed in the construction of some important monuments in Umbria (Italy) using two systems that use concepts and algorithms inherent to Artificial Intelligence: Kohonen self-organizing maps and fuzzy logic. The two systems have been applied to travertine samples belonging to quarries known to be sites of excavation from ancient times and monuments. Tests on quarry samples show a good discriminative power of both methods to recognize the exact provenance of most samples. The application of the systems to monument samples show that most of employed travertine stones were quarried from outcrops occurring in areas close to the towns where monuments have been erected. Results are in good agreement with historical data.

High-resolution geochemistry of volcanic ash highlights complex magma dynamics during the Eyjafjallajokull 2010 eruption

Abstract The April to May 2010 eruption of Eyjafjallajökull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajökull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites.

High-temperature apparatus for chaotic mixing of natural silicate melts

A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10(6) Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

Quantifying magma mixing with the Shannon entropy: Application to simulations and experiments

Abstract We introduce a new quantity to petrology, the Shannon entropy, as a tool for quantifying mixing as well as the rate of production of hybrid compositions in the mixing system. The Shannon entropy approach is applied to time series numerical simulations and high-temperature experiments performed with natural melts. We note that in both cases the Shannon entropy increases linearly during the initial stages of mixing and then saturates toward constant values. Furthermore, chemical elements with different mobilities display different rates of increase of the Shannon entropy. This indicates that the hybrid composition for the different elements is attained at different times generating a wide range of spatio-compositional domains which further increase the apparent complexity of the mixing process. Results from the application of the Shannon entropy analysis are compared with the concept of Relaxation of Concentration Variance (RCV), a measure recently introduced in petrology to quantify chemical exchanges during magma mixing. We derive a linear expression relating the change of concentration variance during mixing and the Shannon entropy. We show that the combined use of Shannon entropy and RCV provides the most complete information about the space and time complexity of magma mixing. As a consequence, detailed information about this fundamental petrogenetic and volcanic process can be gathered. In particular, the Shannon entropy can be used as complement to the RCV method to quantify the mobility of chemical elements in magma mixing systems, to obtain information about the rate of production of compositional heterogeneities, and to derive empirical relationships linking the rate of chemical exchanges between interacting magmas and mixing time.

The characterization of natural gemstones using non-invasive FT-IR spectroscopy: New data on tourmalines

Fourteen samples of tourmaline from the Real Museo Mineralogico of Federico II University (Naples) have been characterized through multi-methodological investigations (EMPA-WDS, SEM-EDS, LA-ICP-MS, and FT-IR spectroscopy). The samples show different size, morphology and color, and are often associated with other minerals. Data on major and minor elements allowed to identify and classify tourmalines as follows: elbaites, tsilaisite, schorl, dravites, uvites and rossmanite. Non-invasive, non-destructive FT-IR and in-situ analyses were carried out on the same samples to validate this chemically-based identification and classification. The results of this research show that a complete characterization of this mineral species, usually time-consuming and expensive, can be successfully achieved through non-destructive FT-IR technique, thus representing a reliable tool for a fast classification extremely useful to plan further analytical strategies, as well as to support gemological appraisals.