Numerical simulation of the 30–45 ka debris avalanche flow of Montagne Pelée volcano,Martinique: from volcano flank collapse to submarine emplacement

Natural Hazards - In November 2015, China government announced that the national carbon emissions trading market is expected to start in 2017. Carbon emission trading system is a raising concern...     

The chemistry of geothermal waters in Iceland. III. Chemical geothermometry in geothermal investigations

New data from geothermal wells in Iceland have permitted empirical calibration of the chalcedony and $\text{Na}\text{K}$ geothermometers in the range of 25–180°C and 25–250°C respectively. The temperature functions are:

$\text{t°C=}\text{1112}\text{4.91?}\text{log SiO}{}_2\text{?273.15}$

$\text{t°C=}\text{933}\text{0.993+}\text{log Na/K}\text{?273.15}$

Concentrations are expressed in ppm. These temperature functions correspond well with the chalcedony solubility data of Fournier (1973) and the thermodynamic data for low-albite/microcline/solution equilibria of Heloeson (1969).A new CO₂ geothermometer is proposed which is considered to be useful in estimating underground temperatures in fumarolic geothermal fields. Its application involves analysis of CO₂ concentrations in the fumarole steam. The temperature function which applies in the range 180?300°C is: logCO₂ = 37.43 + 73192/T- 11829· 10₃/T² + 0.18923T- 86.187·logT where T is in °K and CO₂ in moles per kg of steam.     

Spectrometric analyses in comparison to the physiological condition of heavy metal stressed floodplain vegetation in a standardised experiment

Floodplain ecosystems are affected by flood dynamics, nutrient supply as well as anthropogenic activities. Heavy metal pollution poses a serious environmental challenge. Pollution transfer from the soil to vegetation is still present at the central location of Elbe River, Germany. The goal of this study was to assess and separate the current heavy metal contamination of the floodplain ecosystem, using spectrometric field and laboratory measurements. A standardized pot experiment with floodplain vegetation in differently contaminated soils provided the basis for the measurements. The dominant plant types of the floodplains are: Urtica dioica, Phalaris arundinacea and Alopecurus pratensis, these were also chemically analysed. Various vegetation indices and methods were used to estimate the red edge position, to normalise the spectral curve of the vegetation and to investigate the potential of different methods for separating plant stress in floodplain vegetation. The main task was to compare spectral bands during phenological phases to find a method to detect heavy metal stress in plants. A multi-level algorithm for the curve parameterisation was developed. Chemo-analytical and ecophysiological parameters of plants were considered in the results and correlated with spectral data. The results of this study show the influence of heavy metals on the spectral characteristics of the focal plants. The developed method (depth CR1730) showed significant relationship between the plants and the contamination.     

Fluid inclusion studies in datolite of low grade metamorphic origin from a Jurassic pillow basalt series in northeastern Hungary

The Jurassic pillow basalt blocks in the Szarvask? Unit in the SW-Bükk Mountains are incorporated into an accretionary mélange of Cretaceous age which had been displaced from the Dinarides to NE-Hungary during the Alpine-Carpathian collision. The pillow basalt series is a part of an incomplete remnant of an ophiolite-like sequence from which ultramafic units and sheeted dikes are almost completely absent. At the studied Egerbakta quarry, closely packed pillow, pillow fragmented hyaloclastite breccia and peperitic facies of submarine basaltic volcanism were recognized. Peperitic facies was formed by local admixture of unconsolidated siliciclastic sediment into the basaltic lava. Basaltic pillows contains short and thin prehnite-chlorite-carbonate-quartz veins formed during the interaction of seawater with the cooling lava, as well as cross-cutting datolite-prehnite-quartzchlorite-albite bearing veins. Calcite in the short cooling cracks crystallised from upheated seawater at around 160°C temperature and 0.5?C0.6 kbar pressure (water depth of about 5?C6 km). Datolite precipitations in veins can be classified into at least three different textural-morphological types but all of them contain methane bearing primary fluid inclusion assemblages, with variable methane/water ratios, suggesting an inhomogeneous entrapment from a heterogeneous aqueous-carbonic fluid. End member primary fluid inclusions contain aqueous liquid with methane rich vapour phase and apparently methane only inclusions characterized by liquid phase on room temperature. A combination of results from fluid inclusion microthermometry, Raman spectroscopy (used not only for phase identification but also for determination of salinities) and temperatures calculated from chlorite compositions, show that the precipitation of datolite had taken place from low salinity (0.2?C2 NaCl equiv. mass%) aqueous-methane fluids under increasing temperature and pressure (from 160 to 210°C, and from 0.6 to 1.1 kbar) conditions. The elevated pressures and temperatures in comparison to the submarine hydrothermal processes suggest that the datolite bearing mineral parageneses had been formed during the progression of Alpine very low grade metamorphic processes.     

Molybdenum in icelandic geothermal waters

Molybdenum concentrations in Icelandic geothermal waters lie in the range 1–70 ppb. Warm waters and dilute high-temperature waters which contain high concentrations of sulphide are lowest in molybdenum. No correlation is otherwise observed between molybdenum concentrations and temperature. Surface waters and cold ground waters do not contain detectable molybdenum (<1 ppb). It seems likely that leaching rate is the prime factor in limiting molybdenum levels in these waters. Within individual geothermal fields molybdenum concentrations are either approximately constant or they vary regularly across the field. This regular variation may often be correlated with variations in other solute concentrations and subsurface temperatures and is taken to indicate a control of molybdenum mobility by a temperature dependent equilibrium. The evidence suggests that the solubility of molybdenite is responsible. Molybdenite has not been found in active geothermal systems in Iceland but is known to occur in some New Zealand geothermal systems and it has been identified in hydrothermally altered Tertiary basalt formations at Reydarártindur in southeast Iceland. Boiling and mixing with cold water leads to molybdenite undersaturation and thus these processes favour leaching of molybdenum from the rock. On the other hand, conductive cooling leads to supersaturation which favours removal of molybdenum from solution.     

A new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method

A growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized ‘rigid sponge’ magma. This paper demonstrates that such magma could be idealized as a rheological solid and that the development of non-coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics. Using the finite element method (FEM), we modeled two strain regimes of small magnitudes (plane-strain horizontal simple shear with the shear strain γ of up to 0.30 and plane-strain pure shear of up to 15% shortening) superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix. In the simple shear regime, the phenocrysts slightly rotate toward the shear plane, while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45° or less to the phenocryst fabric. Simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics. By contrast, the vertical phenocryst fabric is maintained in the pure shear regime, and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening (5% shortening after 10 ky in our model). We conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span (first thousands of years) is required to develop magmatic fabric in a pluton for ‘normal’ rates (10⁻¹⁵ to 10⁻¹³ s⁻¹) of tectonic deformation.     

Geology and geochronology of the Betara region in south-southeastern Brazil: Evidence for possible Statherian (1.80–1.75 Ga) and Calymmian (1.50–1.45 Ga) extension events

The results of geological mapping, chemical analysis and radiometric dating of metabasic rocks of Betara Formation, and mapping and dating of those present in the Betara basement nucleus together with mylonitic granodiorite and syenogranite are reported here. U–Pb analysis of bulk zircon fractions from the metabasic rocks of the basement nucleus yielded a Statherian age of 1790 ± 22 Ma, while the metabasic rocks from the upper part of the Betara Formation yielded a Calymmian age between 1500 and 1450 Ma. This age is a minimum for the deposition of the Betara Formation. The older metabasic rocks are associated with post-tectonic, possibly anorogenic syenogranite, while the younger ones are gabbro or very porphyritic ankaramite whose REE patterns are consistent with crystallization from an N-MORB parent magma. The observations and data point to the probable events associated with extensional processes of the end of Paleoproterozoic and early Mesoproterozoic. Similar registers of Statherian (1.80–1.75 Ga) and Calymmian (1.50–1.45 Ga) extensional events are recorded in other parts of the South American and African continents. The Neoproterozoic witnessed the formation and junction of the tectonic slices which formed the Apiaí domain during the assemblage of western Gondwana.     

Comparison of quantitative petrographic, stable isotope and cathodoluminescence data for fingerprinting Czech marbles

Various marbles from both historic quarries and historical artefacts of the Czech Republic were examined in order to make determinations of their provenance. The methodology used was based upon a combination of petrographic image analysis (PIA) of thin sections, stable isotope geochemistry of carbonates, and cathodoluminescence. Multivariate statistical methods (i.e. cluster analysis and discriminant analysis) confirmed the geoscientific relevance of the marble’s different characteristics with a high degree of consistency as well as the enhanced significance of stable C and O isotopes in correlation with the petrographic data. The qualitative cathodoluminescence data provided a useful additional tool to help recognise the fingerprinting of marbles with similar petrographic and/or geochemical characteristics.