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Dietrich, M.
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- PublicationOpen AccessIntrinsic solidification behaviour of basaltic to rhyolitic melts: a cooling rate experimental study(2013)
; ; ; ; ; ; ; ; ; ;Vetere, F.; Dipartimento di Ingegneria e Geologia, Università G. d’Annunzio, via dei Vestini 31, 66100 Chieti Italy. ;Iezzi, G.; Dipartimento di Ingegneria e Geologia, Università G. d’Annunzio, via dei Vestini 31, 66100 Chieti Italy. ;Behrens, H.; Institute for Mineralogy, Leibniz University of Hannover, Callinstr. 3, Hannover, D- 30167, Germany ;Cavallo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Misiti, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dietrich, M.; Institute for Mineralogy, Leibniz University of Hannover, Callinstr. 3, Hannover, D- 30167, Germany ;Knipping, J.; Institute for Mineralogy, Leibniz University of Hannover, Callinstr. 3, Hannover, D- 30167, Germany ;Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Mollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; ; ; Dynamic cooling-induced solidification experiments were run using six silicate glasses along the basalt - rhyolite join (B100= 100 wt % of basalt, R100= 100 wt % of rhyolite), i.e. B100, B80R20, B60R40, B40R60, B20R80 and R100; the glasses directly quenched from 1300 °C after a dwell of 120 minutes (experiment E0) contain 50-400 ppm H2O, << 1 area% μm-sized bubble, and Fe2+/Fetot between 0.34 and 0.46. Experiments were performed in Pt capsules at room pressure and fO2 of air, between 1300 and 800 °C using three different cooling rates of 0.0167, 3 and 30 °C/min; these cooling rates were run two times: E1-E2 experiments at 0.0167°C/min, S1-E3 at 3 °C/min, and E4-E5 at 30 °C/min. In experiments E1 to E5, samples were annealed for 120 minutes at 1300 °C, whereas in the experiment S1 the samples were firstly heated for 30 minutes at 1400 °C followed by a dwell time of 2400 minutes at 1300°C before cooling. In the experiments a preferential crystallization was not observed at the melt/gas interface. B100, B80R20 and B60R40 run-products have a low tendency to preferentially crystallize on Pt walls, while B40R60, B20R80 and R100 are not affected by the presence of Pt substrata. All run-products show very homogeneous textures, except for B60R40 and B40R60 at 0.0167°C/min in the E1 experiment. The duplicates of B40R60 and B60R40 at 0.0167°C/min and B100 at 30 °C/min show relatively large differences in crystal content (> 4 and < 14 area%). B40R60 and B60R40 duplicated run-products have the same amount of earlycrystallized clinopyroxene and spinel, but different contents in lately-formed plagioclase. The run-products with the same starting composition from E3-S1 (3 °C/min) show a high reproducibility in terms of crystal shape, size, and amount (< 4 area%). This demonstrates that the crystallization path is not affected by the different heat treatment above the liquidus temperature, i.e. the time scale of structural re-equilibration (relaxation) and chemical rehomogenization are shorter than our experimental time scale. Possible chemicalheterogeneities on a length scale of several micrometers for R100 and several hundreds of micrometers for B100 can be removed at 1300 °C within 120 minutes. A heat treatment at 1300 °C for 120 minutes significantly reduces the amount of μm-sized bubbles, potentially responsible for the onset of nucleation and unreveals the intrinsic solidification of silicate melts. The experimental reproducibility is low when the cooling path intersects the tip of the time-temperature-transformation (TTT) curves, i.e. when the nucleation rate is near its maximum (Imax). In that case, even small thermal variations in cooling rate and local composition can have large effects on phase abundance and crystal size. Dynamic crystallization experiments can be properly interpreted and compared only if they are texturally homogeneous and the physico-chemical state of the superheated silicate liquid is known. The solidification conditions used in this study mirror those of aphyric lavas and dikes emplaced at shallower crustal levels.302 749 - PublicationRestrictedGlass forming ability and crystallisation behaviour of sub-alkaline silicate melts(2015)
; ; ; ; ; ; ; ; ; ;Vetere, F.; Università Perugia ;iezzi, G.; Università G. D'annunzio Chieti ;Behrens, H.; University Hannover ;Holtz, F.; University Hannover ;Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Misiti, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cavallo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Dietrich, M.; University Hannover; ; ; ; ; ; ; ; been experimentally quantified via cooling-induced solidification approach. GFA is measured by the critical cooling rate Rc, the rate at which a melt solidifies ≤2 area% of crystals. Cooling rates of 9000, 1800, 180, 60, 7 and 1 °C/h have been run between 1300 °C (super-liquidus region) and 800 °C (quenching temperature), at air fO2 and ambient P for six silicate melts with compositions ranging from basalt (B) to rhyolite (R) (i.e., B100, B80R20, B60R40, B40R60, B20R80 and R100) and water contents comprised between 53 (B100) and 384 (B20R80) ppm. The ranges of cooling rates and chemical compositions used in this study are the broadest ever investigated in the Earth sciences. The phase proportions (area%) were determined by image analysis on about 500 back-scattered electron images collected over different magnifications. Phases are glass, clinopyroxene (cpx), spinel (sp) and plagioclase (plg). Sp is ubiquitous with abundance of few area% and nucleates earlier than silicate crystals. Cpx solidifies in all runs except in R100 and its abundance follows asymmetric broad Gaussian-like trends (with tails towards low rates) as a function of cooling rate. Moving from B100 to B40R60 these trends conserve their shape but shift progressively to lower cooling rates and mineral abundances. Plg crystallises only at low cooling rates and in SiO2-poor compositions. Run-products with low amounts of crystals (≤5 area%) clearly show that cpx preferentially nucleates on surfaces of sp, whereas a significant crystallisation of cpx (N5 area%) is observed with decreasing cooling rate and with changing composition from B100 to B20R80. The crystallisation of silicate crystals is related to the chemical diffusivity of components in the melt. Also the initial crystallisation of plg occurs preferentially on cpx. In general, the amount of crystals decreases as the cooling rate increases; however, in some cases, the amount of crystals remains constant or even decreases for B80R20 with decreasing cooling rate. Rc values change over 5 orders of magnitude being b1, 7, 620, 3020, 8020 and 9000 °C/h for R100, B20R80, B40R60, B60R40 and B80R20 and B100, respectively. The variation of Rc can be modelled through NBO/T (nonbridging oxygen per tetrahedron) parameter by the following equation: Rc=a / {1+e−[(NBO/T − b)/c]},where a, b and c are fitting parameters equal to 9214, 0.297 and 0.040, respectively. Similarly to other glass-forming liquids (network, metallic and molecular systems), Rc for natural sub-alkaline silicate melts is inversely related to the reduced glass transition parameter Trg (Trg=Tg / Tm) and can be quantified with the equation Rc= a × Trg−b, where a and b are 1.19 × 10−4 and 28.7, respectively. These results may be used to retrieve the solidification conditions of aphyric, degassed and oxidised lavas; in addition, our data provide general constrains on the crystallisation kinetics of natural crystal-bearing silicate melts erupted on Earth (e.g. lavas with phenocrysts). The relationship between crystal content and cooling rate suggests that the solidification path induced by degassing can be also complex and nonlinear. The growth of crystalswith size up to 1 mm from a nearly anhydrous superheated silicate melt indicates that variable cooling conditions of lavas have to be accounted to discriminate amongminerals formed before, during and after eruptions.Moreover, our results can be used to design glass-ceramics from naturally available easy to find, low-cost starting materials.527 75 - PublicationOpen AccessLooking inside mt. vesuvius(1998)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Italy's Mt.Vesuvius has been slumbering for a long time, but its silence could preface an eruption with potentially disastrous effects for 600,000 people living on the volcano's slopes. To assess the scenario of the next eruption, the National Group of Vol-canology (GNV) of the Italian National Council of Researches (CNR) has fostered research aimed at mitigating eruption risk to the densely populated area. In this framework, researchers have gathered high-resolution seismic tomography data to better understand the internal structure of Mt. Vesuvius. The experiments were carried out during the last 4 years. The data will be used in three-dimensional modeling of the structure of Mt. Vesuvius and underlying upper crust. Seismic velocities and attenuation and density contrasts will be calculated, with special emphasis on the delineation of significant magma reservoirs of more than 1 km in diameter. In modeling Mt. Vesuvius, tools are being developed for using seismogram information to obtain high-quality seismic imaging of heterogeneous structures such as volcanoes221 33