Biotites and associated minerals as markers of magmatic fractionation and deuteric equilibration in granites

Analyses of 80 biotite, alkali feldspar, oligoclase, hornblende, Fe-Ti oxide separates from the coarse-grained granites of a late-hercynian epizonal diapir, the Ploumanac'h complex, Brittany, show that these minerals display a regular concentric cryptic layering related to fractional crystallization. The Ca, Mg, Ba, Sr, Cr, V content of minerals decreases as the Na, Fe, and Rb content increases. Biotites become more dioctahedral towards the outer residual syenogranite, with a correlative K deficiency. Trioctahedral biotites from the inner accumulative monzogranite are secondarily oxidized with a gain of Fe³⁺ and a loss of OH. This alteration id due to the percolation of exsolved fluids rich in H₂O and containing a small amount of CO₂, F, S, Cl. During this autometamorphic stage, trace elements like Rb, Sr are completely redistributed on the scale of hand specimens, with a restricted range of partition coefficients between biotite, perthite and oligoclase. This equilibration occurred at a temperature about 550 ° C and a fluid pressure about 1,000 bars, with f _H2_O probably less than 500 bars. A later stage of fluid circulation along fractures brings up a slight Li metasomatism. Biotites are a sensitive marker of both magmatic and postmagmatic stages of subsolvus or ‘wet’ plutonites.     

Effects of Hydrogel Amendment to Different Soils on Plant Available Water and Survival of Trees under Drought Conditions

The effect of super absorbent polyacrylate (SAP) hydrogel amendment to different soil types on plant available water (PAW), evapotranspiration and survival of Eucalyptus grandis, Eucalyptus citriodora, Pinus caribaea, Araucaria cunninghamii, Melia volkensii, Grevillea robusta, Azadirachta indica, Maesopsis eminii and Terminalia superba was investigated. The seedlings were potted in 3 kg size polythene bags filled with sand, loam, silt loam, sandy loam and clay soils, amended at 0 (control), 0.2 and 0.4% w/w hydrogel. The tree seedlings were allowed to grow normally with routine uniform watering in a glass house set up for a period of eight weeks, after which they were subjected to drought conditions by not watering any further. The 0.4% hydrogel amendment significantly (p < 0.05) increased the PAW by a factor of about three in sand, two fold in silt loam and one fold in sandy loam, loam and clay soils compared to the control. Similarly, the addition of either 0.2 or 0.4% hydrogel to the five soil types resulted in prolonged tree survival compared to the controls. Araucaria cunninghammi survived longest at 153 days, while Maesopsis eminii survived least (95 days) in sand amended at 0.4% after subjection to desiccation. Evapotranspiration was reduced in eight of the nine tree species grown in sandy loam, loam, silt loam and clay soils amended at 0.4% hydrogel. It is probable that soil amendment with SAP decreased the hydraulic soil conductivity that might reduce plant transpiration and soil evaporation.     

The thermal evolution of Corsica as recorded by zircon fission-tracks

New zircon fission-track (ZFT) ages from Corsica record multiple thermal events that can be tied to the structural evolution of the western Mediterranean region. The Corsican zircons have a wide scatter of ZFT grain ages (243–14 Ma), which together define several age domains. Western Corsica consists largely of stable Hercynian basement characterized by ZFT ages in the range 161–114 Ma. We interpret these ages (Late Jurassic–Early Cretaceous) as the product of a long-lived Tethyan thermal event related to continental rifting and subsequent drifting during the separation of the European and African plates and the formation of the Liguro–Piemontese ocean basin. In contrast to Hercynian Corsica, Alpine Corsica (northeast Corsica) experienced widespread deformation and metamorphism in Late Cretaceous(?)–Tertiary time. Dated samples from Alpine Corsica range in age from 112 to 19 Ma and all are reset or partially reset by one or more Alpine thermal events. The youngest ZFT grain ages are from the northernmost Alpine Corsica and define an age population at  24 Ma that indicates cooling after Tertiary thermal events associated with the Alpine metamorphism and the opening of the Liguro–Provençal basin. A less well-defined ZFT age population at  72 Ma is present in both Alpine Corsica and Hercynian basement rocks. The thermal history of these rocks is not clear. One interpretation is that the ZFT population at  72 Ma reflects resetting during a Late Cretaceous event broadly synchronous with the early Alpine metamorphism. Another interpretation is that this peak is related to variable fission-track annealing and partial resetting during the Tertiary Alpine metamorphic event across central to north-eastern Corsica. This partial age resetting supports the presence of a fossil ZFT partial annealing zone and limits the peak temperature in this area below 300 °C, for both the affected pre-Alpine and Alpine units.     

Using SHRIMP zircon dating to unravel tectonothermal events in arc environments. The early Palaeozoic arc of NW Iberia revisited

Abstract Dating of zircon cores and rims from granulites developed in a shear zone provides insights into the complex relationship between magmatism and metamorphism in the deep roots of arc environments. The granulites belong to the uppermost allochthonous terrane of the NW Iberian Massif, which forms part of a Cambro‐Ordovician magmatic arc developed in the peri‐Gondwanan realm. The obtained zircon ages confirm that voluminous calc‐alkaline magmatism peaked around 500 Ma and was shortly followed by granulite facies metamorphism accompanied by deformation at c. 480 Ma, giving a time framework for crustal heating, regional metamorphism, deformation and partial melting, the main processes that control the tectonothermal evolution of arc systems. Traces of this arc can be discontinuously followed in different massifs throughout the European Variscan Belt, and we propose that the uppermost allochthonous units of the NW Iberian Massif, together with the related terranes in Europe, constitute an independent and coherent terrane that drifted away from northern Gondwana prior to the Variscan collisional orogenesis.     

3.8-μm photometry during the secondary eclipse of the extrasolar planet HD 209458b

We report infrared photometry of the extrasolar planet HD 209458b during the time of secondary eclipse (planet passing behind the star). Observations were acquired during two secondary eclipses at the NASA Infrared Telescope Facility (IRTF) in 2003 September. We used a circular variable filter (1.5 per cent bandpass) centred at 3.8 μm to isolate the predicted flux peak of the planet at this wavelength. Residual telluric absorption and instrument variations were removed by offsetting the telescope to nearby bright comparison stars at a high temporal cadence. Our results give a secondary eclipse depth of 0.0013 ± 0.0011, not yet sufficient precision to detect the eclipse, whose expected depth is  ∼0.002 –0.003  . We here elucidate the current observational limitations to this technique, and discuss the approach needed to achieve detections of hot Jupiter secondary eclipses at 3.8 μm from the ground.     

The role of current velocity in structuring eelgrass (Zostera marina L.) meadows

Measurements of velocity profiles, bathymetry, and surface sediment characteristics across eelgrass (Zostera marina L.) meadows yielded information on community development processes and functional attributes of this ecosystem. Height/length ratios of the meadows were positively correlated with tidal current velocity. Low, medium, and high current regimes were separated by surface current velocities of approximately 50 and 90 cm s^?1. Z. marina can tolerate approximately 120–150 cm/sec current velocities in the areas studied. Per cent silt-clay and organic matter content of the surface sediments are negatively associated with shear velocity, suggesting that meadows in high current areas are sources while meadows in low current areas are sinks of autochthonous detritus. Current velocity maintains seagrass meadows at different equilibrium levels (relative climaxes). We theorize these different equilibrium levels provide unequal habitat utilization potentials for the associated faunal community.     

Dependence of normal albedo of lunar regions on wavelength

Normal albedos of thirteen lunar regions are determined at five wavelengths between 4000 and 8000 Å. The deduced values agree with those of the previous investigators except those given by Gehrelset al. (1964) and Van Diggelen (1965). They increase monotonically with the wavelength. At the shortest wavelength, a slight enhancement is detected for most of the regions observed.     

Vorticity waves in a shallow basin

Observed oscillatory current patterns in the southern basin of Lake Michigan, with a distinctive peak in the energy spectrum at a period of about 90 h, are simulated using a linear potential vorticity conservation model. Solutions of the forced vorticity equation in a paraboloidal basin show rotational, oscillatory motions tuned to the low-frequency topographic modes that are very similar to the observed flow patterns. Topography-controlled vorticity waves are excited most effectively by wind episodes with frequency nearly in resonance with the topographic modes. Bottom resistance has no significant effect on the frequency equation; it simply decays the waves slowly in the open lake and more quickly near the coast. Flow patterns of both the gravest free vorticity wave and the corresponding forced wave consist of two opposite circulation cells separated by a null streamline through the center of the basin and rotating cyclonically near the free wave and atmospheric forcing frequencies, respectively. Interactions between the forced and free waves result in an apparent rotational pattern with a frequency the median of the two. A combination of elliptic—paraboloidal basin and shorter period forced modes can approximate the observed Lake Michigan response. Doppler shift, due to the persistence of cyclonic vorticity in the flow field, is also determined to be a factor in shifting the elliptical basin mode to a higher frequency.