1,721,015 research outputs found
La determinazione di P, T, Xi per la definizione multidimensionale delle camere magmatiche a partire dai prodotti eruttati: il caso dell'eruzione di Monte Nuovo (Campi Flegrei) nel 1538.
No full textThe new CISUP facilities for Earth Science at the University of Pisa
Full text linkThe new CISUP facilities for Earth Science at the University of Pisa
Mugnaioli E.*1-2, Folco L.1-2, Masotta M.1-2, Biagioni C.1-2, Paoli G.1 & Capaccioli S.1-3
1 Centro per l'integrazione della strumentazione scientifica, Università di Pisa. 2 Dipartimento di Scienze della Terra, Università di Pisa. 3 Dipartimento di Fisica, Università di Pisa.
[email protected]
Innovative research in Earth sciences, particularly in the fields of mineralogy and petrography, requires the combination of more analytical techniques capable of high-accuracy and/or high spatial resolution. Still, it is rare that a single institution has all the necessary equipment and expertise for a thorough characterization of geological samples. This inevitably hinders the possibility to achieve cutting-edge results in a relatively short time, limiting the national/international attractivity of the facilities and the competitiveness with foreigner research groups.
In 2018, the University of Pisa established the Center for Instrument Sharing (CISUP), an interdepartmental body devoted to the creation of a network of existing facilities and to the pondered acquisition of new large analytical instrumentation (https://cisup.unipi.it/). Through CISUP, the Earth science researchers of the University of Pisa can presently benefit of:
a high-resolution field emission-scanning electron microscope (FE-SEM) operating under high, low and extended low vacuum modes with automated software for large area mapping;
a 193 nm ArF excimer laser ablation system coupled to an inductively coupled plasma-mass spectrometer (LA-ICP-MS);
a high-resolution field emission gun transmission electron microscope (HR-FEG-TEM) equipped with a large-area SDD EDS detector and state-of-the-art electron diffraction systems;
a single-crystal X-ray diffractometer (SC-XRD), with double source (Mo and Cu Kα radiation) and equipped with a detector having the largest active area so far available for lab-instruments.
Moreover, a focused-ion beam (FIB) SEM-FEG for high resolution imaging, EDS large area mapping system, 3D tomography, TEM and APT sample preparation and will be also installed in the next few months.
We believe that the recently installed and to-be-installed CISUP instrumentation will compose an analytical facility of national and international interest, able to valorize the consolidated tradition of the University of Pisa in the view of modern scientific challenges. This new facility will also favor the establishment of national and international scientific collaborations, possibly supporting the whole compartment of the Italian and European Earth sciences
Reactive dissolution of plagioclase in a basaltic melt: A chronometer for pre-eruptive volcanic processes
No full textDissolution and reaction textures of plagioclase phenocrysts in basaltic rocks testify to perturbations of the magmatic system that are frequently associated with pre-eruptive mixing processes. Dissolution-reaction experiments performed at 150 MPa and 1150–1300 °C are used to examine and quantify the timescales of reactive dissolution of plagioclase in a basaltic melt. Simple dissolution occurs under high degrees of plagioclase undersaturation, whereas, at conditions near the plagioclase liquidus, reactive dissolution is expressed by a noticeable decrease in crystal size and the formation of An-rich reaction zones. The total amount of crystal dissolution (ddissolution) and the width of the reaction zone (dreaction) increase with time according to an exponential law, yet more rapidly than what predicted by assuming diffusion in plagioclase as the rate limiting factor. The remarkably fast dissolution rate (∼10–8 m/s) is explained by the formation of planar dissolution interfaces that initially accelerate the dissolution process, whilst the increasing textural maturation of the reaction zone counteracts this effect. A chronometer for retrieving the timescales of reactive dissolution from the width of reaction bands and rims in plagioclase phenocrysts contained in basaltic rocks is derived from the experimental data. The application of this chronometer to Stromboli volcano (Italy), where reaction rims in plagioclase are attributed to the pre-eruptive mixing between a deeper volatile-rich magma (lp-magma) with a degassed magma residing at shallow depths (hp-magma), permits to determine a characteristic timescale of 161±43 min for mixing episodes preceding more energetic eruptions
Trace element partitioning in zoned clinopyroxene as a proxy for undercooling. Experimental constraints from trachybasaltic magmas
No full textSector-zoned clinopyroxene records kinetic effects imposed by variable degrees of magma undercooling,
DT, and can be utilised to track the dynamics of magmatic systems. The partitioning of trace elements
into sectors grown in different crystallographic orientations can be used as a proxy for DT. However,
an experimental assessment of the relationship between trace element zoning and DT has been lacking
to date. Here we present trace element data from a series of undercooling crystallisation experiments on
a primitive trachybasalt from Mt. Etna (Italy), at conditions of crustal storage (400 MPa, NNO + 2), and DT
ranging from 23 to 173 C. Changes in DT were modulated by varying both resting and liquidus temperatures,
the latter via the melt-H2O content of the experiments. The resting temperature was retained for
24 h to ensure the attainment of near-equilibrium conditions.
High-resolution elemental mapping reveals the distribution of trace elements in individual clinopyroxene
zones. Increasing DT drives a shift from polyhedral morphologies with Al-rich prism and Al-poor
hourglass sectors (DT = 23–25 C), to skeletal (DT = 75–123 C) and dendritic (DT = 132–173 C) crystals
with Al-rich skeletons and Al-poor overgrowths. Aluminium-rich zones have higher concentrations of
rare earth elements (REE) and high field strength elements (HFSE) than Al-poor zones across all investigated
DT conditions, and overall, Al, REE and HFSE contents increase with DT. This indicates that tetrahedral
aluminium (TAl) and associated charge-balancing mechanisms govern the incorporation of REE
and HFSE within clinopyroxene. Lattice strain parameters for REE in the M2 site indicate the incorporation
of light relative to heavy REE in clinopyroxene is controlled by competing effects between the strainfree
partition coefficient, D0, and the optimum cation radius, r0. Critically, the middle and heavy REE
switch from incompatible to compatible with increasing DT. Used to model fractional crystallisation,
our data demonstrate that fractionation of clinopyroxene at low DT controls pre-eruptive melt evolution.
Importantly, this indicates crystallisation of clinopyroxene in the deep portions of Mt. Etna’s plumbing
system is not rapid and is unlikely to result in the early formation of dendrites.
We develop a parameterisation of DT based on REE partitioning between experimental clinopyroxene
and coexisting melt, which can be applied to sector-zoned augite crystallising from mafic alkaline magmas,
to reconstruct dynamic processes and thermal pathways during magma transport and storage.
Applied to sector-zoned clinopyroxene microphenocrysts and groundmass microcrysts from the 1974
eccentric eruption at Mt. Etna, our parameterisation tracks an increase in DT with magma ascent and
eruption, following recharge of Cr-rich mafic magma at depth. Sector-zoned clinopyroxene can track
DT variations leading to volcanism at Mt. Etna and could be applied to quantify magma dynamics in other
active volcanoes
A crystal mush perspective explains magma variability at la fossa volcano (Vulcano, Italy)
Full text linkThe eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to pic-ture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging mag-mas and the crystal mushes
Coesite in a Muong Nong-type tektite from Muong Phin, Laos: Description, formation, and survival
No full textWe examined 16 white opaque inclusions exposed on two polished slices of a Muong Nong-type Australasian tektite from Muong Phin, Laos. The inclusions usually consist of a core, surrounded by a froth layer, and a quartz neoblast layer. The cores are composed primarily of a mixture of silica glass, coesite, and quartz in varying proportions. A thin (up to ~4 μm) layer of SiO2-poor glass enriched in FeO, MgO, CaO, Al2O3, and TiO2 is observed as a bright halo in backscattered electron images around the quartz neoblasts and in places contains μm-sized crystals, which may be Fe,Mg-rich spinel. The distribution and textural relationships between the coesite-bearing inclusions and the tektite matrix point to an in situ formation of the coesite due to an impact, rather than to infall, from a nearby impact, into tektite melt produced by the aerial burst of a bolide. The quartz neoblasts probably formed by crystallization of silica melt squeezed out of the inclusion core during the development of the froth layer. The bright halo may be the result of silica diffusing from the adjacent tektite melt into the growing quartz neoblasts. We propose that the survival of coesite was possible due to the froth layer that acted as a heat sink during bubble expansion and then as a thermal insulator
Direct quartz-coesite transformation in shocked porous sandstone from Kamil Crater (Egypt)
Full text linkCoesite, a high-pressure silica polymorph (pressure 3-10 GPa, temperature <3000 K), is a diagnostic feature of shock metamorphism associated with impact cratering on quartz-bearing target rocks. It is preserved as a metastable phase in sedimentary target rocks that experienced peak pressures in excess of similar to 10 GPa, where it typically occurs as intergranular polycrystalline aggregates of microcrystals embedded in silica glass known as "symplectic regions." The presence of coesite in the symplectic regions of rocks experiencing shock conditions beyond the limits of the coesite stability field is a controversial issue. Through a combined scanning and transmission electron microscopy and Raman spectroscopy study of shocked quartzarenites from the 45-m-diameter Kamil Crater (southwest Egypt), we show that coesite in symplectic regions forms through direct subsolidus transformation from quartz, in contrast with the prevailing hypothesis for crystalline targets. The quartz-to-coesite transformation takes place during localized shock-wave reverberation at the beginning of the pore collapse process. Complete pore collapse generates the high temperature regimes responsible for the subsequent production of the embedding silica melts, in part at the expense of the previously formed coesite. This work documents the role of pore collapse in producing localized pressure-temperature-time gradients in shocked porous targets, as predicted by numerical models in the literature
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