Constraints from geochemistry and Sr–Nd isotopes for the origin of albitite deposits from Central Sardinia (Italy)

Major- and trace-element contents and Sr–Nd isotope ratios were determined in albitite, albitized and unaltered late-Variscan granitoid samples from the world-class Na-feldspar deposits of central Sardinia, Italy. The albite deposit of high economic grade has geological, textural, and chemical features typical of metasomatic alteration affecting the host granitoids. Albitization, locally accompanied by chloritization and epidotization, was characterized by strong leaching of Mg, Fe, K, and geochemically similar trace elements, and by a significant increase of Na. Ca, and P were moderately leached in the most metasomatized rocks. Other major (Si, Ti, Ca) and trace elements (U, Th, Y, and Zr), along with light (LREE) and middle (MREE) rare-earth elements, behaved essentially immobile at the deposit scale. The Nd-isotope ratios (0.512098 to 0.512248) do not provide information on the emplacement age of the unaltered late-Variscan granitoids. On the other hand, their Sr-isotope ratios fit an errorchron of 274±29 Ma (1σ error), in fair agreement with all published ages of Sardinian Variscan granitoids. The very low Rb content of albitized rocks precludes application of the Rb–Sr radiometric system to determine the age of albitization. The Sm–Nd system is not applicable either, because the ¹⁴³Nd/¹⁴⁴Nd ratios of albitized rocks and unaltered granitoids overlap. The overlap confirms that Sm and Nd were substantially immobile during albitization. On the other hand, the measured ⁸⁷Sr/⁸⁶Sr ratios of the albitized rocks are appreciably lower than those of the unaltered host granitoids, whereas, their initial Sr-isotope ratios are higher. This seems to suggest that a) albitization was induced by non-magmatic fluids rich in radiogenic Sr, and b) albitization occurred shortly after the granitoid emplacement. This conclusion is supported by Nd isotopes, because unaltered granitoids and albitites fit the same reference isochron at 274 Ma. The fluids acquired radiogenic Sr by circulation through the Lower Paleozoic metasedimentary basement. Specifically, it is estimated that Sr supplied by the non-carbonatic basement represents about 22 wt% of total Sr in albitite.     

Synthetic ANaB(Na x Li1 − x Mg1)CMg5Si8O22(OH)2 (with x = 0.6, 0.2 and 0) P21/m amphiboles at high pressure: a synchrotron infrared study

The high-pressure behavior of three synthetic amphiboles crystallized with space group P2₁/m at room conditions in the system Li₂O–Na₂O–MgO–SiO₂–H₂O has been studied by in situ synchrotron infrared absorption spectroscopy. The amphiboles have compositions ^ANa ^B(Na _x Li_1 − x Mg₁) ^CMg₅ Si₈ O₂₂(OH)₂ with x = 0.6, 0.2 and 0.0, respectively. The high-P experiments up to 32 GPa were carried out on the U2A beamline at Brookhaven National Laboratory (NY, USA) using a diamond anvil cell under non-hydrostatic or quasi-hydrostatic conditions. The two most intense absorption bands in the OH-stretching infrared spectra can be assigned to two non-equivalent O–H dipoles in the P2₁/m structure, bonded to the same local environment ^M1M3Mg₃–OH–^ANa, and pointing toward two differently kinked tetrahedral rings. In all samples these bands progressively merge to give a unique symmetrical absorption with increasing pressure, suggesting a change in symmetry from P2₁/m to C2/m. The pressure at which the transition occurs appears to be linearly correlated to the aggregate B-site dimension. The infrared spectra collected for amphibole ^B(Na_0.2Li_0.8Mg₁) in the frequency range 50 to 1,400 cm⁻¹ also show a series of changes with increasing pressure. The data reported here support the inference of Iezzi et al. (Am Miner 91:479–482, 2006a) regarding a new high-pressure amphibole polymorph.     

CO<Subscript>2</Subscript>-driven large mafic explosive eruptions: the Pozzolane Rosse case study from the Colli Albani Volcanic District (Italy)

Generally, the intensity and magnitude of explosive volcanic activity increase in parallel with SiO₂ content. Pyroclastic-flow-forming eruptions in the Colli Albani ultrapotassic volcanic district (Italy) represent the most striking exception on a global scale, with volumes on the order of tens of cubic kilometres and K-foiditic compositions (SiO₂ even <42 wt.%). Here, we reconstruct the pre-eruptive scenario and event dynamics of the ~456 ka Pozzolane Rosse (PR) eruption, the largest mafic explosive event of the Colli Albani district. In particular, we focus on the driving mechanisms for the unusually explosive eruption of a low-viscosity, mafic magma. Geologic, petrographic and geochemical data with mass balance calculations, supported by experimental data for Colli Albani magma compositions, provide evidence for significant ingestion of carbonate wall rocks by the Pozzolane Rosse K-foiditic magma. Moreover, the scattered occurrence of cored bombs in Pozzolane Rosse pyroclastic-flow deposits records carbonate entrainment even at the eruptive time scale, as also tested quantitatively by thermal modelling of magma–carbonate interaction and carbonate assimilation experiments. We suggest that the addition of free CO₂ from decarbonation of country rocks was the major factor controlling magma explosivity. High CO₂ activity in the volatile component, coupled with magma depressurisation, produced extensive leucite crystallisation at short time scales, resulting in a dramatic increase in magma viscosity and volatile pressurisation, which was manifested a change of eruptive dynamics from early effusion to the Pozzolane Rosse's highly explosive eruption climax.     

Experimental and numerical evaluation of the fundamental period of undamaged and damaged RC framed buildings

This paper deals with the period evaluation of Reinforced Concrete (RC) framed buildings in elastic, yield and severely damaged states. Firstly, period-height relationships either reported in the literature, or obtained from both numerical simulations (eigenvalue analyses) and experimental measurements (ambient vibration analyses) have been examined and compared. Structural types representing low-rise, mid-rise and high-rise RC buildings without earthquake resistant design, widely present in the Italian and European built environment, have been studied. Results have shown high differences between numerical and experimental period values. Period elongation (stiffness degradation) during and after strong ground shaking has been also examined based on results from experimental in situ and laboratory tests performed on some RC framed building structures which suffered moderate-heavy damage. Some comments on the relationship between damage level and period elongation are reported.     

A time-dependent extension of the projected normal regression model for longitudinal circular data based on a hidden Markov heterogeneity structure

The modelling of animal movement is an important ecological and environmental issue. It is well-known that animals change their movement patterns over time, according to observable and unobservable factors. To trace the dynamics of behaviors, to identify factors influencing these dynamics and unobserved characteristics driving intra-subjects correlations, we introduce a time-dependent mixed effects projected normal regression model. A set of animal-specific parameters following a hidden Markov chain is introduced to deal with unobserved heterogeneity. For the maximum likelihood estimation of the model parameters, we outline an expectation–maximization algorithm. A large-scale simulation study provides evidence on model behavior. The data analysis approach based on the proposed model is finally illustrated by an application to a dataset, which derives from a population of Talitrus saltator from the beach of Castiglione della Pescaia (Italy).     

The Balance Between Capturing Phosphorus from Manure and Wastewater and the Demand for Crop Fertilizer in Italy

Phosphorus (P) is an essential nutrient required for plant growth and at the same time a costly pollutant, which can cause eutrophication of water bodies. Modern agriculture relies heavily on mineral fertilisers, which contain phosphorus derived from phosphate rock, because, without regular applications, crop yields would be limited. Since phosphate rock is a non-renewable resource, there are growing concerns regarding future phosphorus scarcity and the sustainability of modern agriculture. For many farmers, animal manure was once a means of maintaining soil fertility, but now it presents a major operational problem. This study evaluated the possibility of recycling phosphorus on a national and regional scale in Italy, using major sources of manure and wastewater. These results were successively compared with an estimate of the agricultural demand for phosphorus. Considering the quantity of phosphorus fertilizer that was applied to the soil–plant system, for the years 2001–2010, the annual phosphorus requirement of Italian crops was about 101,000 t of P. Therefore, the phosphorus source comprising animal manure and civil/industrial waste (117,500 t of P and 40,000 t of P, respectively) could potentially satisfy the average annual agronomic phosphorus demand. Regarding the geographical distribution of phosphorus supply and demand on a regional scale, areas with a large deficit of phosphorus included Calabria, Puglia and Marche. However, when only livestock waste was considered, Sicily, Umbria and Friuli could also be considered to be regions experiencing a phosphorus deficit.

     

Chandra smells a RRAT

“Rotating RAdio Transients” (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities, which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations for the RRAT population. B.M.G. acknowledges the support of NASA through LTSA grant NAG5-13023 and of an Alfred P. Sloan Fellowship.