Geochronology of the medium to high-grade metamorphic units of the Peloritani Mts., Sicily

The Peloritani Mountains are a fragment of an orogen variably attributed to the Alpine or Hercynian orogeny. On the basis of ³⁹Ar-⁴⁰Ar, U-Pb and Rb-Sr dating, the main metamorphism of the two medium–high grade metamorphic units, the Mela and Aspromonte Units, and most of the thrusting responsible for stacking the orogenic edifice are seen to be Hercynian. The main thrusting of the Aspromonte Unit over the lower grade units took place at 301±2 Ma. Brittle deformation during Tertiary reactivation of Hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector. Our dataset shows a great complexity and we propose to unravel it by considering different levels of information. To first order, the Mela and Aspromonte Units differ in their metamorphic paths and their geochronological evolution. The Mela Unit shows generally younger ages (Carboniferous) than the Aspromonte Unit and, unlike the latter, was extensively retrogressed in greenschist facies. The Aspromonte Unit is itself geochronologically heterogeneous. Proterozoic ages are preserved both in titanite and in amphibole relics of one tectonic subunit; Devonian to Carboniferous amphibole ages are found in different other subunits; tertiary overprint is minor and spatially limited. We propose to consider the chronologically heterogeneous subunits as accreted pre-Hercynian terranes amalgamated late during the Hercynian orogeny. Micas in both units give scattered Mesozoic ³⁹Ar-⁴⁰Ar and Rb-Sr ages, with evidence for heterochemical mica generations. We interpret them as a result of widespread hydrothermal circulation event(s). Tertiary overprint is generally absent, with the exception of a small area near Messina where biotite and muscovite underwent a complex recrystallisation history in the interval between 48 and 61 Ma.An erratum to this article can be found at     

Late Holocene environmental history on Tristan da Cunha, South Atlantic, based on diatom floristic changes and geochemistry in sediments of a volcanic crater lake

A late Holocene diatom stratigraphy of Bottom Pond (37°05′S, 12°17′W) was studied and interpreted to infer paleolimnological and climate changes on Tristan da Cunha, South Atlantic. The diatom flora of Bottom Pond is dominated by meroplanktonic Aulacoseira alpigena and A. distans and a benthic/epiphytic flora including Achnanthes spp., Naviculadicta spp., Eunotia taxa and Frustulia rhomboides. The flora also includes an important terrestrial and aerophytic component, consisting of several Diadesmis spp., Navicula lapidosa, Nitzschia terrestris and some Pinnularia spp., at times dominating the flora. Peaks of high terrestrial diatom abundances and low abundances and concentrations of Aulacoseira spp., correspond to periods of increased magnetic susceptibility and are interpreted to be the result of increased catchment erosion and/or precipitation leading to enhanced in-wash of species living in the soils around the lake. The diatom record of Bottom Pond most likely registers both local responses to increased erosion in the catchment as well as climatic change of a more regional character. Comparisons with the geochemical record in 2nd Pond on Nightingale Island show a correspondence between the two data sets at 2,000–1,750 cal yrs BP, most likely evidence of increased precipitation in the Tristan da Cunha region. The Tristan da Cunha archipelago is situated at the northern limit of the Southern hemisphere west wind belt and stronger and/or a northward shift of the westerlies, are probably the main causes of the precipitation changes.     

Energy dissipation models for RC members and structures

The unloading parameters of hysteretic models for RC members are given in terms of their shear-span-to-depth ratio and the viscous damping used to model other energy dissipation sources. They reflect the energy dissipation in full post-yield load cycles in 534 tests of rectangular or circular members. Pre-yield hysteretic energy dissipation—ignored if the model is elastic till yielding—amounts in the tests to a mean viscous damping around 8.5% and can be considered in nonlinear response-history analysis through a new model which combines constant elastic stiffness in virgin loading with hysteretic energy dissipation both before and after yielding. Models with linear behavior till yielding and hysteretic energy dissipation only after it come closer to the results of the new model if viscous damping is 5%.     

Galactic evolution of 7LI: observational clues for models

Different stellar sources may have contributed to the ⁷Li enrichmentof the Galaxy: type-II supernovae, novae, and AGB stars. In the latter case, the interplay between the Hot Bottom Burning (HBB) process (via the Cameron-Fowler mechanism) and a very high mass-loss rate before the evolution off the AGB (the so-called ‘superwind’ phase), can lead to a significant production of ⁷Li from low- and intermediate-mass AGB stars (Travaglio et al., 2001). We have now undertaken an observational campaign aimed at constraining our stellar and Galactic models, with a twofold goal: (i) to assemble a compilation of high-resolution spectra of Galactic, unevolved (i.e. dwarfs), warm(spectral type F) stars, in a selected metallicity range (-1.0 ≤>[Fe/H] ≤ -0.3), using the ESO 1.5m telescope and the FEROS spectrograph; (ii) to carry out a Li survey among a sample of selected AGB stars, to investigate the possible correlation between⁷Li abundance (when detected) and mass-loss rate. This revised version was published online in September 2006 with corrections to the Cover Date.     

Tree-ring growth variability in the Austrian Alps: the influence of site, altitude, tree species and climate

We present an extensive new network of ring-width chronologies, comprising data from 100 sites within the Austrian Eastern Alps, made up of multiple tree species. Principal components analysis and cluster analysis were used to identify five separate high-frequency tree-growth signals from these data. Tree-growth variability at these sites is explained by site altitude and species differences that moderate the effects of the annually varying climatic forcing on tree growth. Recently developed, two-century long gridded climate data sets for the Greater Alpine Region were used to assess the relationship between climate and tree growth. Tree growth at low altitudes is controlled mainly by spring-summer moisture availability. At high altitudes precipitation is no longer a limiting factor and growth is mostly determined by summer temperature. In the intermediate altitudinal range, we did not find any direct relationships with specific climatic variables. High-altitude chronologies suitable for reconstructing past temperatures and low-altitude chronologies suitable for reconstructing past precipitation were identified.     

Exploring the 7:4 mean motion resonance—II: Scattering evolutionary paths and resonance sticking

In our preliminary study, we have investigated basic properties and dynamical evolution of classical TNOs around the 7:4 mean motion resonance with Neptune (a∼43.7 AU), motivated by observational evidences that apparently present irregular features near this resonance (see [Lykawka and Mukai, 2005a. Exploring the 7:4 mean motion resonance—I. Dynamical evolution of classical trans-Neptunian objects (TNOs). Space Planet. Sci. 53, 1175-1187]; hereafter “Paper I”). In this paper, we aim to explore the dynamical long-term evolution in the scattered disk (but not its early formation) based on the computer simulations performed in Paper I together with extra computations. Specifically, we integrated the orbital motion of test particles (totalizing a bit more than 10,000) placed around the 7:4 mean motion resonance under the effect of the four giant planets for the age of the Solar System. In order to investigate chaotic diffusion, we also conducted a special simulation with on-line computation of proper elements following tracks in phase space over 4-5 Gyr. We found that: (1) A few percent (1-2%) of the test particles survived in the scattered disk with direct influence of other Neptunian mean motion resonances, indicating that resonance sticking is an extremely common phenomenon and that it helps to enhance scattered objects longevity. (2) In the same region, the so-called extended scattered TNOs are able to form via very long resonance trapping under certain conditions. Namely, if the body spends more than about 80% of its dynamical lifetime trapped in mean motion resonance(s) and there is the action of a k+1 or (k+2)/2 mean motion resonance (e.g., external mean motion resonances with Neptune described as (j+k)/j with j=1 and 2, respectively). According to this hypothetical mechanism, 5-15% of current scattered TNOs would possess thus probably constituting a significant part of the extended scattered disk. (3) Moreover, considering hot orbital initial conditions, it is likely that the trans-Neptunian belt (or Edgeworth-Kuiper belt) has been providing members to the scattered disk, so that scattered TNOs observed today would consist of primordial scattered bodies mixed with TNOs that came from unstable regions of the trans-Neptunian belt in the past.Considering the three points together, our results demonstrated that the scattered disk has been evolving continuously since early times until present.     

Stellar parameters of young brown dwarfs

We present X‐shooter observations of two brown dwarf candidates. We focus on the determination of stellar parameters and their errors. The targets, an accreting class II and a non‐accreting class III objects, are members of the σ Orionis star‐forming region. We derive the spectroscopic spectral types from the VIS spectrum and the stellar parameters. We find that the uncertainties on the stellar parameters have a minor effect on the determination of the mass accretion rate for the accreting star, thus confirming that the discrepancies between the mass accretion rate estimates found with different (simultaneous) tracers are probably due to different physical conditions where the accretion/wind indicators are produced (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observing GRB host galaxies with the integral field unit of X‐shooter

Using the integral field unit of X‐shooter at VLT, we have recovered the first velocity fields of GRB host galaxies at redshift <0.6. This facility is able to recover not only the velocity fields from almost all emission lines thanks to an unrivaled wavelength coverage, but also to recover maps of physical properties. We present the preliminary analysis of X‐shooter/IFU observations dedicated to the study of GRB host galaxies undertaken in the frame of the Italian‐French GTO program. Our goal is to understand the physical processes at the origin of the GRB by analyzing in detail the spatial distributions of the kinematics, metallicities, extinction, star‐formation, and how they are inter‐related (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Change-point analysis for serially correlated summit temperatures in the Romanian Carpathians

Characterizing climatic changes in the high-altitude mountain regions helps scientists and policy makers understand the effects of such changes on water resources, economic development, and the health of ecosystems. This paper proposes a change-point analysis to determine the time and magnitude of summer temperature changes in the summit areas of Romanian Carpathians between 1961 and 2007. Due to their altitude, massiveness, and position, Romanian Carpathians are an important barrier for different types of air masses between Western and Southeastern Europe. The results show that the change in summer temperatures occurred shortly after 1980. The average magnitude of this change is consistent with changes occurring in other parts of Southern Europe in the same time period although the magnitude of changes at individual weather stations may differ substantially. We aided our analysis by a statistical method based on regression models with serially correlated ARMA errors.