A Hercynian suture zone in Sardinia : geological and geochemical evidence

Abstract

The Hereynian basement of Northern Sardinia consists of two main teetonometamorphic complexes : the Southern Paleozoic Low to Medium Grade Metamorphic Complex (LMGMC) and the Northern (Precaimbrian ?) High Grade Metamorphic Complex (HGMC). These complexes are separateli bu the “Posada-Asinara Line” which is a several kilometer-wide mylonitie belt consisting of micaschist. parag-neiss and quartzite that cuts across all Northern Sardinia and contains scattered hodies of amphibolites with granulile and eclogite facies relies.

Major element composition of ampbibolites indicates they were derived from metamorphosed basalts of tholciitie affinity. REE and the relative abundances of HKS elements strongly suggest an oceanic basaltie prololith (N- and T-typc MORB). A whole-rock Sm-Nd isochron for the amphibolite protoliths yields an age of ea. 960 Ma.

The Northern Sardinia basement can he interpreted as a continental collisional zone with the “Posada-Asinara Line” representing a suture zone squeezed between a crustal nappe (HGMC), which represents the overthrust continental margin. and (he inner portion of the Varisean orogenie wedge, which represents the underthrust continental margin with its Paleozoic cover (LMGMC).

Geological and geochemical evidence indicate that the “Posada-Asinara Line” may he considered as part of the South European Hereynian Suture Zone.     

Moment tensor inversion for two micro-earthquakes occurring inside the Háje gas storage facilities, Czech Republic

Broadband data from the P?íbram seismological network was used to investigate the source of two earthquakes, with magnitudes M _w ?=?0.2 and 0.4 respectively, occurring in the period of October–November 2009 in the Háje natural gas storage area (Czech Republic). Both events were located inside the limits of the storage area and at depths similar to those of the underground caverns where the gas is stored. We applied an inversion technique using the software ISOLA for moment tensor retrieval in order to assess the source process of both events and recognize whether a significant isotropic component existed that could be interpreted as a possible cavern collapse. We also performed an uncertainty analysis so as to confirm the reliability of the focal mechanism solutions and we controlled the consistency between the inverted focal mechanisms and those calculated using the P-waves first motions. Our results showed that the nodal plane orientation, the centroid depth, and the magnitude remained stable. Furthermore, we calculated synthetic waveforms for collapse-type ruptures and compared them with the original records. The match between the synthetic and the original data was very poor supporting the interpretation of the shear character of the events. The combination of the inversion results, which indicated significant double-couple components and of the synthetic tests, which supported the inexistence of an isotropic component at the source, led to the conclusion that the possibility of rocks falling from the ceiling of the caverns or a cavern collapse is highly unlikely.     

Ground motion observations and simulation for local earthquakes in the Campi Flegrei volcanic area

Ground motion produced by low magnitude earthquakes can be used to predict peak values in high seismic risk areas where large earthquakes data are not available. In the present work 20 local earthquakes (M_D∈[?0.3, 2.2]) occurred in the Campi Flegrei caldera during the last decade were analyzed. We followed this strategy: empirical relations were used to calibrate synthetic modeling, accounting for the source features and wave propagation effects. Once the source and path parameters of ground motion simulation were obtained from the reference data set, we extrapolated scenarios for stronger earthquakes for which real data are not available. The procedure is structured in two steps: (1) evaluation of ground motion prediction equation for Campi Flegrei area and assessment of input parameters for the source, path and site effects in order to use the finite fault stochastic approach (EXSIM code); (2) simulation of two moderate-to-large earthquake scenarios for which only historical data or partial information are available (M_w4.2 and M_w5.4). The results show that the investigated area is characterized by high attenuation of peak amplitude and not negligible site effects. The stochastic approach has revealed a good tool to calibrate source, path and site parameters on small earthquakes and to generate large earthquake scenario. The investigated magnitude range represents a lower limit to apply the stochastic method as a calibration tool, due to the small size of involved faults (fault length around 200/300 m).     

Supermassive black holes, star formation and downsizing of elliptical galaxies

The overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass, poses a serious problem for all current models of galaxy formation. Here, we improve on the one-zone chemical evolution models for elliptical galaxies by taking into account positive feedback produced in the early stages of supermassive central black hole growth. We can account for both the observed correlation and the scatter if the observed anti-hierarchical behaviour of the AGN population couples to galaxy assembly and results in an enhancement of the star formation efficiency which is proportional to galactic mass. At low and intermediate galactic masses, however, a slower mode for star formation suffices to account for the observational properties.     

Spatial and temporal patterns in the movement of Procambarus clarkii, an invasive crayfish

Introduced in Italy in the 1980s for aquaculture enterprises, the red swamp crayfish, Procambarus clarkii, has invaded many water bodies, giving rise to breeding populations that now threaten freshwater ecosystems. An understanding of the spatial behaviour of this crayfish could be the baseline for future research aimed at control and management. Following the same pattern as other freshwater decapods, P. clarkii, studied in an irrigation ditch system in Florence, Tuscany, displayed stationary phases (several marked individuals were recaptured in the area) interposed with nomadic bursts of movement (many marked crayfish disappeared). With a few exceptions, nocturnal activity prevailed in almost all the seasons in two different analysed habitats (irrigation ditches and the Massaciuccoli Lake, Lucca). However, in the laboratory, locomotion occurred mostly at daytime. Although still prevailing, P. clarkii's nocturnal activity appeared puzzling, because some of its major predators are nocturnal and this species is mostly herbivorous. The intercalation between stationary and wandering phases leaves open further promising studies on social structures in the field.     

On the dependence ofQ metallicity index from basic parameters of stellar evolution

The possible dependence of Van den Bergh'sQ parameter on the mass distribution function in globular clusters is investigated. The resulting independence within the observational errors assures thatQ is available as index of the chemical composition and age of the clusters.