Carbonate-bearing mantle peridotite xenoliths from Spitsbergen: phase relationships,mineral compositions and trace-element residence

 Carbonates of mantle origin have been found in xenoliths from Quaternary basaltic volcanoes in NW Spitsbergen. The carbonates range from dolomite to Mg-bearing calcite and have high Mg-numbers [Mg/(Mg+Fe)=(0.92–0.99)]. In some samples they occur interstitially, e.g. at triple junctions of silicate minerals and appear to be in textural and chemical equilibrium with host lherzolite. Most commonly, however, the carbonates make up fine-grained aggregates together with (Ca,Mg)-rich olivine and (Al,Cr,Ti)-rich clinopyroxene that typically replace spinel, amphibole, and orthopyroxene as well as primary clinopyroxene and olivine. Some lherzolites contain amphibole and apatite that appear to have formed before precipitation of the carbonates. In situ analyses by proton microprobe show very high contents of Sr in the clinopyroxene, carbonates and apatite; the apatite is also very rich in LREE, U, Th, Cl, Br. Disseminated amphibole in carbonate-bearing rocks is very poor in Nb and Zr, in contrast to vein amphibole and mica from carbonate-free rocks that are rich in Nb and Zr. Overall, the Spitsbergen xenoliths provide evidence both for the occurrence of primary carbonate in apparent equilibrium with the spinel lherzolites (regardless of the nature of events that emplaced them) and for the formation of carbonate-bearing pockets consistent with metasomatism by carbonate melts. Calcite and amorphous carbonate-rich materials occur in com- posite carbonate-fluid inclusions, veins and partial melting zones that appear to be related to fluid action in the mantle, heating of the xenoliths during their entrainment in basaltic magma, and to decompression melting of the carbonates. Magnesite is a product of secondary, post-eruption alteration of the xenoliths. Received: 6 October 1995/Accepted: 17 June 1996     

The Coastal Springs of Southern Kerala,SW India – Hydrology and Water Quality Assessment

Spring water is a reliable source of potable water in many parts of the world. Uplifted coasts of the Southern Kerala host many high yielding cold water springs which emerge from the sand - clay interface of the Neogene outcrops. Lack of adequate studies on the hydrological and water quality aspects of these springs is challenging the wise use and management of these springs. Therefore, an attempt has been made to map the locations and study the water quality of the free-falling type of springs emerging from the Neogene outcrops exposed on the cliffed coasts of Southern Kerala, especially falling within the jurisdiction of Kollam and Thiruvananthapuram districts. A total of 31 springs from four distinct geomorphic settings has been located in our survey conducted in 2008–2009 period. But, our recent survey carried out in March 2017 revealed that about 10 % of the springs were dried out due to various reasons. The total spring water discharge during 2017 was about 450 liters/minute against the total discharge of 800 liters/minute in 2007–08 period. In general, the hydrochemistry of spring waters is dominated by alkali and strong acids, i.e. alkali-chloride type. Most of the hydrochemical parameters exhibit a great degree of seasonal and spatial variations and are well within the permissible limits (with the exception of pH) for all four groups of springs. The low mineral contents may be attributed to minimal weathering from silicate-rich rocks and insignificant leaching from soil due to infiltration from anthropogenic activities. The spring water quality in all the four groups of the study area is bacteriologically contaminated and therefore proper disinfection is required before human consumption. Most of the spring water samples are classified to be “excellent to good” for irrigation and is not expected to cause any salinity hazard.     

On the Influence of a Simple Microphysics Parametrization on Radiation Fog Modelling: A Case Study During ParisFog

A detailed numerical simulation of a radiation fog event with a single column model is presented, which takes into account recent developments in microphysical parametrizations. One-dimensional simulations are performed using the computational fluid dynamics model Code_Saturne and the results are compared to a very detailed in situ dataset collected during the ParisFog campaign, which took place near Paris, France, during the winter 2006–2007. Special attention is given to the detailed and complete diurnal simulations and to the role of microphysics in the fog life cycle. The comparison between the simulated and the observed visibility, in the single-column model case study, shows that the evolution of radiation fog is correctly simulated. Sensitivity simulations show that fog development and dissipation are sensitive to the droplet-size distribution through sedimentation/deposition processes but the aerosol number concentration in the coarse mode has a low impact on the time of fog formation.     

Numerical Simulations of the Microscale Heterogeneities of Turbulence Observed on a Complex Site

We simulate the microscale heterogeneities of turbulent variables observed at a complex site for different wind directions. The atmospheric computational fluid dynamics (CFD) results are compared with an ensemble of 36 months of data collected at the experimental site SIRTA “Site Instrumental de Recherche par Télédétection Atmosphérique”, located near Paris (France) in a semi-urban environment. The experimental data show that the normalized turbulent kinetic energy (TKE) k/U ² (where k is TKE and U is the wind speed) at 10-m height, for two different locations, is highly dependent on wind direction and strongly influenced by trees. These measurements show a strong increase of the normalized TKE downstream of the forest canopies with a large variability within the 36-month period in part due to the variation of the tree foliage. The numerical simulations are carried out using the CFD code Code_Saturne with the standard k?ε closure, in neutral stratification. The buildings are taken into account explicitly in the mesh and the forested areas are modelled with two approaches: the classical roughness wall law and a drag porosity. A comparison has been performed between the calculated values and the median of measured values of the normalized TKE and the normalized friction velocity, for each wind sector of 10°. A very good agreement is obtained with the drag porosity model, whereas the classical roughness law leads to a strong underestimation downstream of the forested areas. However, this large improvement of the results using the drag porosity model can only be obtained with a refinement of the grid, especially in forested areas, and an accurate land-use map.     

Partitioning of lanthanides and Y between immiscible silicate and fluoride melts, fluorite and cryolite and the origin of the lanthanide tetrad effect in igneous rocks

Some F-rich granitic rocks show anomalous, nonchondritic ratios of Y/Ho, extreme negative Eu anomalies, and unusual, discontinuous, segmented chondrite-normalised plots of rare earth elements (REE). The effects of F-rich fluids have been proposed as one of the explanations for the geochemical anomalies in the evolved granitic systems, as the stability of nonsilicate complexes of individual rare earths may affect the fluid-melt element partitioning. The lanthanide tetrad effect, related to different configurations of 4f-electron subshells of the lanthanide elements, is one of the factors affecting such complexing behaviour. We present the first experimental demonstration of the decoupling of Y and Ho, and the tetrad effect in the partitioning of rare earths between immiscible silicate and fluoride melts. Two types of experiments were performed: dry runs at atmospheric pressure in a high-temperature centrifuge at 1100 to 1200°C, and experiments with the addition of H₂O at 700 to 800°C and 100 MPa in rapid-quench cold-seal pressure vessels. Run products were analysed by electron microprobe (major components), solution-based inductively coupled plasma mass spectrometry (ICP-MS) (REE in the centrifuged runs), and laser ablation ICP-MS (REE and Li in the products of rapid-quench runs). All the dry centrifuge runs were performed at super-liquidus, two-phase conditions. In the experiments with water-bearing mixtures, minor amounts of aqueous vapour were present in addition to the melts. We found that lanthanides and Y concentrated strongly in the fluoride liquids, with two-melt partition coefficients reaching values as high as 100-220 in water-bearing compositions. In all the experimental samples, two-melt partition coefficients of lanthanides show subtle periodicity consistent with the tetrad effect, and the partition coefficient of Y is greater than that of Ho. One of the mixtures also produced abundant fluorite (CaF₂) and cryolite (Na₃AlF₆) crystals, which enabled us to study fluorite-melt and cryolite-melt REE partitioning. REE concentrations in fluorite are high and comparable to those in the fluoride melt. However, fluorite-melt partition coefficients appear to depend mostly on ionic radii and show neither significant tetrad anomalies, nor differences in Y and Ho partitioning. In contrast, REE concentrations in cryolite are low (∼5-10 times lower than in the silicate melt), and cryolite-melt REE partitioning shows very strong tetrad and Y-Ho anomalies. Our results imply that Y-Ho and lanthanide tetrad anomalies are likely to be caused mainly by aluminofluoride complexes, and the tetrad REE patterns in natural igneous rocks can result from fractionation of F-rich magmatic fluids.     

Polar aromatic biomarkers of Miocene-aged Chukurovo resinite and correlation with a progenitor macrofossil

Functionalised aromatic constituents of Chukurovo resinite are compared here with the chemical composition of a macrofossil assigned paleobotanically as Taxodium dubium (Sternb.) Heer. Terpenoids and lipids of fossil wood tissue embedded in a clay sediment were extracted and analyzed for comparison. The information was interpreted in relation to the biomarker compositions of different conifer families, as well as to the effects of contamination by inward migration of organic matter from the adjacent sediments.Many of identified geolipids, i.e., alkanes, alkanols, alkan-2-ones, and steranes/triterpanes have no chemosystematic value because they are ubiquitous in the plant kingdom. Ferruginol, sugiol, and products of their diagenetic transformations were identified as the dominant specific biomarkers in the resinite. Ferruginol and its analogues were the most abundant diterpenoids in Taxodium dubium sample. Thus, the biomarker composition of the extractable matter of the resinite strongly suggests that species of Cupressaceae contributed significantly to the Chukurovo paleoenvironment.     

Transtensional fault-termination basins: an important basin type illustrated by the Pliocene San Jose Island basin and related basins in the southern Gulf of California, Mexico

Transtensional basins are sparsely described in the literature compared with other basin types. The oblique‐divergent plate boundary in the southern Gulf of California has many transtensional basins: we have studied those on San Jose island and two other transtensional basins in the region. One major type of transtensional basin common in the southern Gulf of California region is a fault‐termination basin formed where normal faults splay off of strike‐slip faults. These basins suggest a model for transtensional fault‐termination basins that includes traits that show a hybrid nature between classic rift and strike‐slip (pull‐apart) basins. The traits include combinations of oblique, strike‐slip and normal faults with common steps and bends, buttress unconformities between the fault steps and beyond the ends of faults, a common facies pattern of terrestrial strata changing upward and away from the faults into marine strata, small fault blocks within the basin that result in complex lateral facies relations, common Gilbert deltas, dramatic termination of the margin of the basin by means of fault reorganization and boundary faults dying and an overall short basin history (few million years). Similar transtensional fault‐termination basins are present in Death Valley and other parts of the Eastern California shear zone of the western United States, northern Aegean Sea and along ancient strike‐slip faults.     

Computational Fluid Dynamical Modelling of Concentration Fluctuations in an Idealized Urban Area

Turbulent mixing induces variability in concentration that is important in many applications, such as reactive plumes, risk assessments or odour impact analyses (when the effects can have time scales on the order of a second). In urban canopies, the variability may be modified by the presence of buildings. Our purpose is to study concentration fluctuation variance in built-up areas using an Eulerian approach. We performed numerical simulations with the computational fluid dynamics model Mercure_Saturne, which is a three-dimensional model adapted to atmospheric flow and pollutant dispersion. We use a k − ϵ turbulence closure and predict the concentration variance with a transport equation model. The model performance is evaluated with the near-full scale experiment MUST (Mock Urban Setting Test), a field experiment conducted in Utah’s West Desert Test Center. The modelled root-mean-square of the concentration fluctuations is compared to measurements for 20 of the MUST trials. The model shows good agreement with the measurements, with the fraction of predictions within a factor of two of observations of 60.1%, with better results for horizontal lines of detectors than for the detectors on vertical masts (with fractions of predictions within a factor of two of observations of respectively 66.4% and 52.6%). The influence of different parameters on the fluctuation variance is also studied and we show the importance of taking into account the stability of the stratification when modelling the turbulent kinetic energy.     

Petrogenesis of 3.15 Ga old Banasandra komatiites from the Dharwar craton,India: Implications for early mantle heterogeneity

Spinifex-textured.magnesian(MgO 25 wt.%) komatiites from Mesoarchean Banasandra greenstone belt of the Sargur Group in the Dharwar craton,India were analysed for major and trace elements and~(147,146)Sm-~(143,142)Nd systematics to constrain age,petrogenesis and to understand the evolution of Archean mantle.Major and trace element ratios such as CaO/Al_2O_3.Al_2O_3/TiO_2,Gd/Yb,La/Nb and Nb/Y suggest aluminium undepleted to enriched compositional range for these komatiites.The depth of melting is estimated to be varying from 120 to 240 km and trace-element modelling indicates that the mantle source would have undergone multiple episodes of melting prior to the generation of magmas parental to these komatiites.Ten samples of these komatiites together with the published results of four samples from the same belt yield ~(147)Sm-~(143)Nd isochron age of ca.3.14 Ga with an initial ε_(Nd)(f) value of+3.5.High precision measurements of ~(142)Nd/~(144)Nd ratios were carried out for six komatiite samples along with standards AMES and La Jolla.All results are within uncertainties of the terrestrial samples.The absence of~(142)Nd/~(144)Nd anomaly indicates that the source of these komatiites formed after the extinction of ~(146)Sm,i.e.4.3 Ga ago.In order to evolve to the high ε_(Nd)(t) value of +3.5 by 3.14 Ga the time-integrated ratio of~(147)Sm/~(144)Nd should be 0.2178 at the minimum.This is higher than the ratios estimated,so far,for mantle during that time.These results indicate at least two events of mantle differentiation starting with the chondritic composition of the mantle.The first event occurred very early at ~4.53 Ga to create a global early depleted reservoir with superchondritic Sm/Nd ratio.The source of Isua greenstone rocks with positive ~(142)Nd anomaly was depleted during a second differentiation within the life time of ~(146)Sm,i.e.prior to 4.46 Ga.The source mantle of the Banasandra komatiite was a result of a differentiation event that occurred after the extinction of the ~(146)Sm,i.e.at 4.3 Ga and prior to 3.14 Ga.Banasandra komatiites therefore provide evidence for preservation of heterogeneities generated during mantle differentiation at4.3 Ga.     

Analysis of Titan CH4 3.3 μm upper atmospheric emission as measured by Cassini/VIMS

After molecular nitrogen, methane is the most abundant species in Titan’s atmosphere and plays a major role in its energy budget and its chemistry. Methane has strong bands at 3.3 μm emitting mainly at daytime after absorption of solar radiation. This emission is strongly affected by non-local thermodynamic equilibrium (non-LTE) in Titan’s upper atmosphere and, hence, an accurate modeling of the non-LTE populations of the emitting vibrational levels is necessary for its analysis. We present a sophisticated and extensive non-LTE model which considers 22 CH₄ levels and takes into account all known excitation mechanisms in which they take part. Solar absorption is the major excitation process controlling the population of the v₃-quanta levels above 1000 km whereas the distribution of the vibrational energy within levels of similar energy through collisions with N₂ is also of importance below that altitude. CH₄-CH₄ vibrational exchange of v₄-quanta affects their population below 500 km. We found that the ν₃ → ground band dominates Titan’s 3.3 μm daytime limb radiance above 750 km whereas the ν₃ + ν₄ → ν₄ band does below that altitude and down to 300 km. The ν₃ + ν₂ → ν₂, the 2ν₃ → ν₃, and the ¹³CH₄ν₃ → ground bands each contribute from 5% to 8% at regions below 800 km. The ν₃ + 2ν₄ → 2ν₄and ν₂ + ν₃ + ν₄ → ν₂ + ν₄ bands each contribute from 2% to 5% below 650 km. Contributions from other CH₄ bands are negligible. We have used the non-LTE model to retrieve the CH₄ abundance from 500 to 1100 km in the southern hemisphere from Cassini-VIMS daytime measurements near 3.3 μm. Our retrievals show good agreement with previous measurements and model results, supporting a weak deviation from well mixed values from the lower atmosphere up to 1000 km.