Alteration, HFSE mineralisation and hydrocarbon formation in peralkaline igneous systems: Insights from the Strange Lake Pluton, Canada

Two characteristics of peralkaline igneous rocks that are poorly understood are the extreme enrichment in HFSE, notably Zr, Nb, Y and REE, and the occurrence of fluid inclusions dominated by methane and higher hydrocarbons. Although much of the HFSE enrichment can be explained by magmatic processes, the common intense alteration of the parts of the peralkaline intrusions most enriched in these elements suggests that hydrothermal processes also play an important role in HFSE enrichment. Likewise, although the origin of the higher order hydrocarbons that occur as inclusions in these rocks is still debated, there is strong evidence that at least in some cases their formation involved hydrothermal processes. The issues of HFSE enrichment and hydrocarbon formation in peralkaline intrusions are examined using data from the Strange Lake pluton, a small, middle-Proterozoic intrusion of peralkaline granite in northeast Canada. This pluton contains some of the highest concentrations of Zr, REE and Y ever reported in an igneous body, and is characterised by abundant hydrocarbon-dominated fluid inclusions in rocks that have been hydrothermally altered, including those that form a potential HFSE ore zone. We show that HFSE at Strange Lake were partly concentrated to near exploitable levels as a result of their transport in a high salinity magmatic aqueous liquid, and that this fluid coexisted immiscibly with a carbonic phase which reacted with hydrogen and iron oxides generated during the associated hydrothermal alteration to produce hydrocarbons via a Fischer–Tropsch synthesis. As a result, hydrocarbons and HFSE mineralization are intimately associated. We then go on to show that hydrothermal alteration, HFSE mineralisation and hydrocarbons are also spatially associated in other peralkaline complexes, and present a model to explain this association, which we believe may be applicable to any peralkaline intrusion where HFSE enrichment was accompanied by calcium metasomatism, hematisation and hydrothermal fluorite. We also suggest that, even where these criteria are not satisfied, hydrothermally enriched HFSE and hydrocarbons will be intimately associated simply because they are products of the same initial magmatic fluid. Finally, we speculate that the association of HFSE and hydrocarbons may in some cases actually be genetic, if, as seems possible, unmixing or effervescence of a reduced carbonic fluid from the original magmatic fluid caused changes in temperature, pH, fO₂ or the activity of volatile ligands sufficient to induce the deposition of HFSE minerals.     

Five subglacial lakes and one of Antarctica's thickest ice covers newly determined by radio echo sounding over the Vostok-Dome C region

Radio echo sounding (RES) measurements were collected from 1995 to 2003 during Italian Antarctic expeditions over the Vostok-Dome C region. The data collected allow for the reconstruction of a bedrock elevation map between the Belgica Highlands and the Aurora Subglacial Basin (112.0ø - 124.0ø E; 74.0ø - 78.0ø S). Moreover, analysis of the RES data has revealed one of the thickest ice covers in Antarctica (4755 Ø 16 m; 118.321ø E, 76.059ø S) as well as five new subglacial lakes.     

The relationship between seismic deformation and deep-seated gravitational movements during the 1997 Umbria–Marche (Central Italy) earthquakes

This paper re-evaluates the origin of some peculiar patterns of ground deformation in the Central Apennines, observed by space geodetic techniques during the two earthquakes of the Colfiorito seismic sequence on September 26th, 1997. The surface displacement field due to the fault dislocation, as modelled with the classic Okada elastic formulations, shows some areas with high residuals which cannot be attributed to non-simulated model complexities. The residuals were investigated using geomorphological analysis, recognising the geologic evidence of deep-seated gravitational slope deformations (DSGSD) of the block-slide type. The shape and direction of the co-seismic ground displacement observed in these areas are correlated with the expected pattern of movement produced by the reactivation of the identified DSGSD. At least a few centimetres of negative “Line of Sight” ground displacement was determined for the Costa Picchio, Mt. Pennino, and Mt. Prefoglio areas. A considerable horizontal component of movement in the Costa Picchio DSGSD is evident from a qualitative analysis of ascending and descending interferograms. The timing of the geodetic data indicates that the ground movement occurred during the seismic shaking, and that it did not progress appreciably during the following months. This work has verified the seismic triggering of DSGSD previously hypothesized by many researchers. A further implication is that in the assessment of DSGSD hazard seismic input needs to be considered as an important cause of accelerated deformation.     

Source parameters and stress release of seismic sequences occurred in the Friuli-Venezia Giulia region (Northeastern Italy) and in Western Slovenia

The source parameters of the major events of a swarm and of two seismic sequences, occurred in the Friuli area (Northeastern Italy) and in Western Slovenia, were estimated. The Claut swarm (C96) occurred since the end of January to June 1996, with a M_D 4.3 major shock and it appears composed of three sub-sequences. The two sequences are the Kobarid sequence (K98) started on April 12, 1998 with a M_D 5.6 mainshock and the M.te Sernio (S02) sequence caused by the February 14, 2002 earthquake (M_D = 4.9). Acceleration and velocity data recorded by the local seismic network of the Istituto Nazionale di Oceanografia e di Geofisica Sperimenale (OGS) and corrected for attenuation, were employed to estimate seismic moments and radiated energies. Source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the Brune stress drop, the apparent stress and the RMS stress drop. On the whole, seismic moments range from 1.7 × 10¹² to 1.1 × 10¹⁷ N m, and radiated energies are in the range 10⁶–10¹³ J. Brune stress drops are scattered and do not show any evidence of a self-similarity breakdown for sources down to 130 m radius. The radiated seismic energy scales as a function of seismic moment, with a slope of the scaling relation that decreases for increasing seismic moments.The mechanism of stress release was analyzed by computing the ɛ parameter of Zuniga [Zuniga, R., 1993. Frictional overshoot and partial stress drop. Which one? Bull. Seismol. Soc. Am. 83, 939–944]. The K98 and S02 sequences are characterized by a wide range of the ɛ parameter with stress drop mechanism varying from partial locking to overshoot cases. The ɛ values of the C96 swarm are more homogeneous and close to the Orowan's condition. The radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases. We therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences. For this purpose, we also estimated the source parameters of two other sequences occurred in the area, with mainshocks of M_D 4.1 and 5.1, respectively. We found a positive correlation between the Brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks.     

Hydrodynamical Simulations of Galaxy Clusters

In my contribution I discuss the relevance that hydrodynamical simulation of clusters can play to understand the ICM physics and to calibrate mass estimates from X-ray observable quantities. Using hydrodynamical simulations, which cover quite a large dynamical range and include a fairly advanced treatment of the gas physics (cooling, star formation and SN feedback), I show that scaling relations among X-ray observable quantities can be reproduced quite well. At the sametime, these simulations fail at accounting for several observational quantities, which are related to the cooling structure of the ICM: the fraction of stars, the temperature profiles and the gas entropy in central cluster regions. This calls for the need of introducing in simulations suitable physical mechanisms which should regulate the cooling structure of the ICM.     

Application of biomarkers for assessing the biological impact of dredged materials in the Mediterranean: the relationship between antioxidant responses and susceptibility to oxidative stress in the red mullet (Mullus barbatus)

In the period 1997-2000, approximately 1,800,000 m3 of material dredged from the Port of Leghorn was discharged into a sea dumping site located 14 miles from the coast. The red mullet (Mullus barbatus) was used as a bioindicator species for monitoring the biological impact of these discharges on a geographical and temporal scale. Organisms were sampled over three years (1998-2000) at different stations and several biomarkers, both of exposure and effect, were analyzed. Bioavailability of specific classes of pollutants was evaluated by analyzing levels of metallothioneins, the activity of cytochrome P450 1A (CYPIA) and of glutathione S-transferases. Among biomarkers of effect, special attention was paid to the balance between prooxidant challenge and antioxidant defenses, and to the appearance of damage caused by oxidative stress. The analyses of the main components of the antioxidant system included superoxide dismutase, catalase, glutathione peroxidases, glutathione reductase, glyoxalase I and II, and total glutathione. These data were integrated with the measurement of total oxyradical scavenging capacity (TOSC) as an indication of the overall biological resistance to toxicity of different forms of oxyradicals (peroxyl radicals, hydroxyl radicals and peroxynitrite). Results indicated a biological impact in organisms sampled near the disposal site; the impact was particularly evident during 1999 and mainly related to organic chemicals such as PAH. Exposure to these pollutants also caused variations in the levels and activity of several antioxidants. The analysis of TOSC, however, revealed that the overall capacity of specific tissues of organisms to absorb various oxidants was not seriously compromised when challenged with increased prooxidant pressures. Variations of single antioxidants were useful in revealing early warning "biological responses", while integration with TOSC analyses indicated if such changes also reflect a more integrated and functional "biological effect" with possible consequences at the organisms level. The red mullet appears to be a useful sentinel species for a biomarker approach to monitoring impact caused by dredged materials.     

Position and velocity perturbations in the orbital frame in terms of classical element perturbations

The transformation of classical orbit element perturbations to perturbations in position and velocity in the radial, transverse and normal directions of the orbital frame is developed. The formulation is given for the case of mean anomaly perturbations as well as for eccentric and true anomaly perturbations. Approximate formulas are also developed for the case of nearly circular orbits and compared with those found in the literature.     

The mapping of Kaula's solution into the orbital reference frame

Kaula's celebrated solution to the problem of satellite motion in the gravitational field of a rigid body is transformed to give the perturbation spectra in both position and velocity in the radial, transverse and normal directions of the orbital reference frame. This work is an extension and a refinement of the theory of orbital perturbations due to the geopotential previously published by Rosborough and Tapley (1987).