On the stability of magmatic cordierite and new thermobarometric equations for cordierite-saturated liquids

In this work, we have reviewed a large compositional dataset (571 analyses) for natural and experimental glasses to understand the physico-chemical and compositional conditions of magmatic cordierite crystallization. Cordierite crystallizes in peraluminous liquids (A/CNK ≥1) at temperatures ≥750 °C, pressures ≤700 MPa, variable H₂O activity (0.1–1.0) and relatively low fO₂ conditions (≤NNO ? 0.5). In addition to A/CNK ratio ≥1, a required condition for cordierite crystallization is a Si + Al cation value of the rhyolite liquid of 4 p8O (i.e. calculated on the 8 oxygen anhydrous basis), which is consistent with low Fe³⁺ contents and the absence or low content of non-bridging oxygens (NBO). This geochemical condition is strongly supported by the rare, if not unique, structure of cordierite where the tetrahedral framework is composed almost exclusively of Si and Al cations the sum of which is equal to 4 p8O [i.e. (Mg,Fe)_8/9Al_16/9Si_20/9O₈], indicating that aluminium (and cordierite) saturation is limited by rhyolite liquids with Al = 4 ? Si. Indeed, synthetic or natural systems with Al > 4 ? Si always show metastable glass-in-glass separation or crystallization of refractory minerals such as corundum (Al_16/3O₈) and aluminosilicates (Al_16/5Si_8/5O₈). Multivariate regression analyses of literature data for experimental glasses coexisting with magmatic cordierite produced two empirical equations to independently calculate the T (±13 °C; ME, maximum error = 29 °C) and P (±16 %; ME% = 27 %) conditions of cordierite saturation. The greatest influence on the two equations is exerted by H₂O_melt and Al concentrations, respectively. Testing of these equations with other thermobarometric constraints (e.g. feldspar-liquid, GASP, Grt–Bt and Grt–Crd equilibria) and thermodynamic models (NCKFMASHTO and NCKFMASH systems) was successfully performed for Crd-bearing rhyolites and residual enclaves from San Vincenzo (Tuscany, Italy), Morococala Field (Bolivia) and El Hoyazo (Spain). The reliability of each calculated P–T pair was graphically evaluated using the minimum and maximum P–T–H₂O relationships for peraluminous rhyolite liquids modified after the metaluminous relationships in this work. Both P–T calculations and checking can be easily performed with the attached user-friendly spreadsheet (i.e. Crd-sat_TB).     

Numerical simulations of the 1963 Vajont landslide, Italy: application of 1D Lagrangian modelling

On 9 October 1963, a rock mass of about 250 millions m³, with a front width of 1,850 m, a mean thickness of about 200 m and a length of 350–400 m, detached from Mt Toc, on the left side of the Vajont valley, NE Italy, and collapsed into the reservoir created by a 261 m high dam. About 40 millions m³ of water was displaced, climbed up 200 m on the opposite side and then destroyed the little town of Longarone causing more than 2,000 casualties. This event is well known and was the object of numerous technical and scientific studies, especially in the two decades following the disaster. This work proposes a re-examination of the matter, focusing on the numerical modelling of the landslide, and is carried out by using a 1D numerical code based on a Lagrangian approach. The model is properly conceived for cases with slide length prevailing on width. When the slide width is comparable or prevailing on length, as is the case of the Vajont slide, the mass is first partitioned into a number of longitudinal long and narrow sub-slides. The Vajont mass was subdivided into six strips and the motion of each sub-slide was computed. The knowledge of the final deposit position allowed us to constrain the value of some relevant parameters characterizing the slide motion, the most interesting being the friction coefficient μ, that we varied in order to obtain the best-fit between calculated and observed deposits. Taking into account the additional constraint that all sub-slides move with the same or at least with similar speed, and introducing a global misfit based on deposit and velocity misfits, we were able to show that solutions minimizing the global misfit exhibit a relevant difference between the basal friction coefficients of the western and of the eastern sides of the sliding surface, with the former being significantly smaller (0.14–0.16) than the latter (0.32–0.34).     

Ir Observations Of An Outburst In Comet Hale-Bopp (C/1995 O1)

The comet Hale-Bopp (C/1995 O1) has been observed in the infrared (1–2.5 μm) with the Nordic Optical Telescope (NOT) equipped with the Arcetri NICMOS3 camera (ARNICA). Two observational campaigns, each one lasting about one week, were made when the comet heliocentric distance was about 3 AU. The first campaign was at the end of August and the second at the end of September 1996. During both runs two major outbursts were observed, the more intense of them started the day before the beginning of the second run. In the images recorded during the first three nights (24.8–26.8 Sept.) of the second run a dust shell expanding in the northern quadrant with a projected velocity of 0.14–0.28 km/s is clearly evident. The dust production rate increased by at least a factor ≈3 at the time of the outburst. Also evident on the first night is a change in the IR color that is well correlated with the dust shell. This is an indication that the material released by the outburst has a different composition and/or size distribution than that in the “quiescent” dust coma. In this paper we present preliminary results about the evolution and the photometric characteristics of the dust shell. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Simulation Method for Semicollisional Plasmas

We present a one dimensional kinetic simulation model which can be used to simulate the stationary state of a semicollisional plasma. Results of a simple simulation are presented and compared to Fokker-Planck calculations. The model is particularly well suited for the diluted solar atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical properties of Laue lenses for hard X-rays (>60 keV)

We report on preliminary results obtained with a Monte Carlo (MC) code developed to study the optical properties of Laue lenses for astro-physical observations. The MC code is written in the Python programming language and uses open source libraries. Among the physical quantities which can be investigated with the MC code, we paid our attention mainly to the estimation of the effective area, field of view (FOV) and point spread function (PSF) of the lens for observation of sources on-axis and off-axis.     

Evolution of Br/Cl ratios in fumarolic salammoniac from Vulcano (Aeolian Islands,Italy)

 Bromine/chlorine ratios in salammoniac samples, collected from 1983 to 1994 at the Fossa crater fumaroles of Vulcano (Aeolian Islands), were determined. The data obtained in this work have been compared to those obtained by Coradossi et al. (1985) in order to carry out a systematic study of the Br/Cl ratio variations since 1977. Br/Cl ratios range from 0.04 to 0.29. The Br/Cl ratio variations observed have been interpreted as the result of different contributions among deep and shallow components feeding the fumarolic fluids of Vulcano. The Br/Cl increases, which occurred from 1977 to 1979, in 1983–1984 and in 1992–1993, have been connected to an increased input of magmatic gases. Received: 10 November 1995 / Accepted: 12 July 1996     

The evolution of rural areas influenced by large-scale farming: four case studies from Hungary

GeoJournal - In order to study complex transformation of rural areas in the long term, our paper aims to integrate the concepts of rural restructuring and evolutionary economic geography. We argue...     

A comparative study on a complex URM building: part I—sensitivity of the seismic response to different modelling options in the equivalent frame models

Bulletin of Earthquake Engineering - The paper presents the comparison of the results of nonlinear static analyses carried out using six software packages (SWs) available at professional level and...