Sulphur solubility in andesitic to basaltic melts: implications for Hekla volcano

The solubility of sulphur in sulphide-saturated, H₂O-bearing basaltic–andesitic and basaltic melts from Hekla volcano (Iceland) has been determined experimentally at 1,050°C, 300 and 200 MPa, and redox conditions with oxygen fugacity (logfO₂) between QFM−1.2 and QFM+1.1 (QFM is a quartz–fayalite–magnetite oxygen buffer) in the systems containing various amounts of S and H₂O. The S content of the H₂O-rich glasses saturated with pyrrhotite decreases from 2,500 ppm in basalt to 1,500 ppm in basaltic andesite at the investigated conditions. Furthermore, the reduction of water content in the melt at pyrrhotite saturation and fixed T, P and redox conditions leads to a decrease in S concentration from 2,500 to 1,400 ppm for basaltic experiments (for H₂O decrease from 7.8 to 1.4 wt%) and from 1,500 to 900 ppm (for H₂O decrease from 6.7 to 1.7 wt%) for basaltic andesitic experiments. Our experimental data, combined with silicate melt inclusion investigations and the available models on sulphide saturation in mafic magmas, indicate that the parental basaltic melts of Hekla were not saturated with respect to sulphide. During magmatic differentiation, the S content in the residual melts increased and might have reached sulphide saturation with 2,500 ppm dissolved S. With further magma crystallization, the S concentration in the melt was controlled by the sulphide saturation of the magma, decreasing from ~2,500 to 900 ppm S.     

Timescales of convection in magma chambers below the Mid-Atlantic ridge from melt inclusions investigations

Closed hopper and complex swallowtail morphologies of olivine microcrysts have been described in the past in both mid-oceanic ridge basalts and subaerial tholeitic volcanoes and indicate fluctuations in magma undercooling. We describe similar morphologies in a Mid-Atlantic ridge pillow basalt (sample RD87DR10), and in addition we estimate the duration of temperature fluctuations required to produce these textures as follows: (1) Pairs of melt inclusions are arranged symmetrically around the centre of hopper crystals and each pair represents a heating–cooling cycle. Using the literature olivine growth rates relevant to the observed morphologies, and measuring the distance between two successive inclusions, we estimate the minimum time elapsed during one convection cycle. (2) The major element composition of melt inclusions (analysed by electron microprobe) was found to be in the range of the boundary layer measured in the glass surrounding the olivines, irrespective of their size. Several major elements demonstrate that this boundary layer results from rapid quenching on the seafloor, and not from crystal growth at depth, implying the inclusions had the same composition as the surrounding magma when they were sealed. Using diffusivity of slow diffusing elements such as Al₂O₃, we estimate the minimum time required for inclusion formation. These two independent approaches give concordant results: each cooling–heating cycle lasted between a few minutes and 1 h minimum. Thus, these crystals probably recorded thermal convection in small magmatic bodies (a dyke or shallow magma chamber) during the last hour or hours before eruption.     

Fines adsorption on nanoparticle-coated surface

Fluid flow through porous media is inherently associated with the detachment and migration of fine particles. The migration of fine particles and ensuing clogging is the main reason of flow rate decrease in porous media. Nanoparticle coating can be a promising method to prevent fines’ detachment and migration by changing electrical surface forces between the pore wall surface and the fine particles. In this study, the attraction and adhesion forces of the nanoparticle-coated surface are measured by atomic force microscope. The effect of the nanoparticle coating on the fines adsorption efficiency is then investigated. The results show that there is an increase in the adhesion force on the nanoparticle-coated surface and the significant improvement of the fines adsorption capacity by the nanoparticle coating. The research results are relevant to other research areas whenever migrating fines cause engineering problems.     

Seasonal dynamics and stoichiometry of the planktonic community in the NW Mediterranean Sea: a 3D modeling approach

The 3D hydrodynamic Model for Applications at Regional Scale (MARS3D) was coupled with a biogeochemical model developed with the Ecological Modular Mechanistic Modelling (Eco3M) numerical tool. The three-dimensional coupled model was applied to the NW Mediterranean Sea to study the dynamics of the key biogeochemical processes in the area in relation with hydrodynamic constraints. In particular, we focused on the temporal and spatial variability of intracellular contents of living and non-living compartments. The conceptual scheme of the biogeochemical model accounts for the complex food web of the NW Mediterranean Sea (34 state variables), using flexible plankton stoichiometry. We used mechanistic formulations to describe most of the biogeochemical processes involved in the dynamics of marine pelagic ecosystems. Simulations covered the period from September 1, 2009 to January 31, 2011 (17 months), which enabled comparison of model outputs with situ measurements made during two oceanographic cruises in the region (Costeau-4: April 27–May 2, 2010 and Costeau-6: January 23–January 27, 2011).     

The ancient Chinese notes on hydrogeology

The ancient Chinese notes on hydrogeology are summarized and interpreted, along with records of some related matters, like groundwater exploration and utilization, karst springs, water circulation, water conservation and saline-land transformation, mine drainage, and environmental hydrogeology. The report focuses only on the earliest recorded notes, mostly up until the Han Dynasty (206 BC??C?AD 25). Besides the references cited, the discussion in this report is based mainly on archaeological material, the preserved written classic literature, and some assumptions and/or conclusions that have been handed down in legends to later ages. Although most material relates to ancient China, the lessons learned may have practical significance worldwide. Compared to other contemporary parts of the world, ancient China, without doubt, took the lead in the field of groundwater hydrology. The great achievements and experience of the Chinese ancestors should provide motivation and inspiration for hydrogeologists to carry out their scientific research and exploration passionately and actively.     

Water organisation at the solid–aqueous solution interfaceOrganisation de l'eau à l'interface solide–solution aqueuse

The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631.     

Tropical variability and stratospheric equatorial waves in the IPSLCM5 model

The atmospheric variability in the equatorial regions is analysed in the Earth System Model pre-industrial simulation done at IPSL in the framework of CMIP5. We find that the model has an interannual variability of about the right amplitude and temporal scale, when compared to the El-Niño Southern Oscillation (ENSO), but that is too confined to the western Pacific. At the intra-seasonal periods, the model variability lacks of large-scale organisation, and only produces one characteristic Madden-Julian Oscillation every 10 winters typically. At shorter time-scales and in the troposphere, the model has Rossby and Kelvin Convectively Coupled Equatorial Waves (CCEWs), but underestimates the Kelvin CCEWs signal on OLR. In the model stratosphere, a composite analysis shows that the Temperature and velocities fluctuations due to the Kelvin waves are quite realistic. In the model nevertheless, the stratospheric waves are less related to the convection than in the observations, suggesting that their forcing by the midlatitudes plays a larger role. Still in the model, the Kelvin waves are not predominantly occurring during the life cycle of the tropospheric Kelvin CCEWs, a behaviour that we find to be dominant in the observations. The composite analysis is also used to illustrate how the waves modify the zonal mean-flow, and to show that the model Kelvin waves are too weak in this respect. This illustrates how a model can have a reasonable Kelvin waves signal on the velocities and temperature, but can at the same time underestimate their amplitude to modify the mean flow. We also use this very long simulation to establish that in the model, the stratospheric equatorial waves are significantly affected by ENSO, hence supporting the idea that the ENSO can have an influence on the Quasi-Biennial Oscillation.     

Phase changes and thermodynamic properties of CaTiO3. Spectroscopic data,vibrational modelling and some insights on the properties of MgSiO3 perovskite

The effect of pressure (up to 21 GPa at room temperature) and temperature (up to 1570 K at room pressure) on the Raman spectrum of CaTiO₃ is presented. No significant changes, which could be attributed to a major structural change, are observed in the spectra up to 22 GPa. The pressure shifts of the Raman modes can be related to a significant compression of the Ti-O bond. Discontinuous changes in the spectra upon heating may be related to phase changes observed by calorimetry and X-ray diffraction. The important temperature shifts of some low-frequency modes can be related to an increase in the Ti-O-Ti angle in agreement with the X-ray data showing a decrease of the structural distortion with increasing temperature. These data are compared to those available for MgSiO₃-perovskite and show that CaTiO₃ is a good structural analogue for MgSiO₃-perovskite. The present spectroscopic data are used to calculate the specific heat and entropy of CaTiO₃. The role of the low frequency modes in the calculations is emphasized. Good agreement is observed between calculated and experimentally determined values in the 0–1300 K temperature range. A similarly defined model is proposed for MgSiO₃-perovskite. It is found that the entropy lies between 57 and 64 J/mol/K at 298 K and between 190 and 200 J/mol/K at 1000 K in agreement with the values inferred from experimental equilibrium data. Finally we briefly discuss the values of the Grüneisen parameters of both perovskites inferred from macroscopic and microscopic data.     

Thermal decomposition process in algaenan of Botryococcus braunii race L. Part 2: Molecular dynamics simulations using the ReaxFF reactive force field

This paper reports ReaxFF MD simulation results on pyrolysis of a molecular model of the algaenan Botryococcus braunii race L biopolymer, specifically, ReaxFF predictions on the pyrolysis of prototypical chemical structures involving aliphatic chain esters and aldehydes. These preliminary computational experiments are then used to analyze the thermal cracking process within algaenan race L biopolymers. The simulations indicate that the thermal decomposition of the algaenan biopolymer is initiated by the cleavage of a C–O bond in the ester group, followed by the release of carbon dioxide. We also observe a significant, strongly temperature dependent, release of ethylene. This degradation mechanism leads to products similar to those observed in pyrolysis experiments, validating this computational approach.     

Emplacement of Semail–Emirates ophiolite at ridge–trench collision

The Oman‐Emirates is the largest and best‐exposed ophiolite; consequently, it has attracted significant interest among scientists, together with serious conflicts. Most geologists regard this ophiolite as having formed in an intra‐oceanic subduction zone before being accreted to the Arabian continent. Here, we propose an alternative scenario, supported by detailed field observations and integrated geophysics. The smaller Emirates part of the ophiolite was forced into a nearby continent, in the pre‐collision stage of Tethyan closure. The contraction led to the exhumation of the mantle floor of segmented basins accreted in a rifted system similar to the present‐day Gulf of California. The implied high temperature–high pressure metamorphism and the range of geochemical signatures were introduced during the process of rifting, whereas the larger Oman ophiolite was emplaced by obduction onto and along the subducting continental shore. This Ridge–Trench–Transform system might call for a new process to obduct over continents in particular Tethyan ophiolites.